An MIT research team led by Professor Darrell Irvine has developed a novel kind of vaccine adjuvant: a nanoparticle that can help to stimulate the immune system to generate a stronger response to a vaccine. These nanoparticles contain saponin, a compound derived from the bark of the Chilean soapbark tree, along with a molecule called MPLA, each of which helps to activate the immune system.

The adjuvant has been incorporated into an experimental HIV vaccine that has shown promising results in animal studies, and this month, the first human volunteers will receive the vaccine as part of a phase 1 clinical trial run by the Consortium for HIV/AIDS Vaccine Development at the Scripps Research Institute. MIT News spoke with Irvine about why this project required an interdisciplinary approach, and what may lie ahead.

Q: What are the special features of the new nanoparticle adjuvant that help it create a more powerful immune response to vaccination? 

A: Most vaccines, such as the Covid-19 vaccines, are thought to protect us through B cells making protective antibodies. Development of an HIV vaccine has been made challenging by the fact that the B cells that are capable of evolving to produce protective antibodies — called broadly neutralizing antibodies — are very rare in the average person. Vaccine adjuvants are important in this scenario to ensure that when we immunize with an HIV antigen, these rare B cells become activated and get a chance to participate in the immune response.

We particularly discovered that this new adjuvant, which we call SMNP (short for saponin/MPLA nanoparticles), is particularly good at helping more B cells enter germinal centers, the specialized location in lymph nodes where high affinity antibodies are produced. In animal models, SMNP also has shown unique mechanisms of action: Administering antigens with SMNP leads to better antigen delivery to lymph nodes (through increases in lymph flow) and better capture of the antigen by B cells in lymph nodes.

Q: How did your lab, which generally focuses on bioengineering and materials science, end up working on HIV vaccines? What obstacles did you have to overcome in the development of this adjuvant?

A: About 15 years ago, Bruce Walker approached me about getting involved in the HIV vaccine effort, and recruited me to join the Ragon Institute of MGH, MIT, and Harvard as a member of the steering committee. Through the Ragon Institute, I met colleagues in the Scripps Consortium for HIV/AIDS Vaccine Development (CHAVD), and we realized there was a tremendous opportunity to directly contribute to the HIV vaccine challenge, working in partnership with experts in immunogen design, structural biology, and HIV pathogenesis.

As we carried out study after study of SMNP in preclinical animal models, we realized the adjuvant had really amazing effects for promoting anti-HIV antibody responses, and the CHAVD decided this was worth moving forward to testing in humans. A major challenge was transferring the technology out of the lab to synthesize large amounts of the adjuvant under GMP (good manufacturing process) conditions for a clinical trial. The initial contract manufacturing organization (CMO) hired by the consortium to produce SMNP simply couldn’t get a process to work for scalable manufacturing.

Luckily for us, a chemical engineering graduate student, Ivan Pires, whom I co-advise with Paula Hammond, head of MIT’s Department of Chemical Engineering, had developed expertise in one particular processing technique known as tangential flow filtration during his undergraduate training. Leveraging classic chemical engineering skills in thermodynamics and process design, Ivan stepped in and solved the process issues the CMO was facing, allowing the manufacturing to move forward. This to me is what makes MIT great — the ability of our students and postdocs to step up and solve big problems and make big contributions when the need arises.

Q: What other diseases could this approach be useful for? Are there any plans to test it with other types of vaccines?

A: In principle, SMNP may be helpful for any infectious disease vaccine where strong antibody responses are needed. We are currently sharing the adjuvant with about 30 different labs around the world, who are testing it in vaccines against many other pathogens including Epstein-Barr virus, malaria, and influenza. We are hopeful that if SMNP is safe and effective in humans, this will be an adjuvant that can be broadly used in infectious disease trials.

Retroviruses cannot replicate on their own — they must insert their genetic code into the DNA of a host and exploit the host cell's resources to make more copies of themselves, furthering infection. Some retroviruses only infect cells as they divide, when the nuclear envelope that protects the host's genetic material breaks down, making it easily accessible. HIV-1 is a type of retrovirus, called a lentivirus, that can infect non-dividing cells.

HIV-1 delivers its genome into the nucleus by packaging it into a large, cone-shaped structure called a capsid — but the exact mechanism has remained elusive for decades. Travel through the nuclear envelope occurs through, and is regulated by, nuclear pores, doughnut-shaped protein assemblies. Human cells have about 2,000 nuclear pores perforating the nuclear envelope. Some earlier evidence suggested that the capsid remains intact during its delivery into the nucleus — but this created a dimensional conundrum. The cone-shaped HIV-1 capsid is about 120 nanometers long and 60 nm wide — too large, researchers thought, to fit through the opening of the nuclear pore, measured at only 43 nm wide.

Members of the Schwartz Lab at MIT, in the Department of Biology, became interested in this question when a postdoc in the lab used cryo-electron tomography, slicing up sections of frozen cells to examine structures, to show that nuclear pores in the nuclear envelope are larger than 43nm. They deflate and shrink, it turns out, when removed from their native conditions. In native conditions, the nuclear pore complex is about 60nm wide — wide enough to accommodate the HIV-1 capsid.

Knowing that it could fit, a question remained: How can the capsid navigate the dense mesh of spaghetti-like proteins that act like a sieve in the nuclear pore channel? That spaghetti-like mesh allows small cargo to diffuse through, but prevents large cargo from entering unless it is escorted by proteins called nuclear transport receptors.

In an open-access paper published today in Nature, researchers present evidence that the HIV-1 capsid mimics the cell's transport receptors to traverse the nuclear pore.

To support that conclusion, the researchers showed three things in vitro: that an HIV-1 capsid can deliver cargo through a nuclear pore analog; that the capsid can interact with the sieve of proteins in the nuclear pore channel; and that the capsid targets the nuclear pore in the absence of native transport proteins.

Nuclear transport receptors escort large cargo through the nuclear pore by “batting away” the spaghetti-like mesh of proteins inside the channel — like someone holding your hand and guiding you across a crowded dance floor. The HIV-1 capsid interacts with the spaghetti-like proteins, but its purpose is more like a Trojan horse — the capsid encapsulates the viral cargo, protecting it from detection in the cytoplasm and as it enters the nuclear pore complex.

"What's really amazing about cells is that they are incredibly complex. What's really difficult about studying cells is that they are incredibly complex," jokes co-first author Erika Weiskopf, a graduate student in the Schwartz lab. "Biochemists are constantly trying to find ways to study their system in a simplified context, but still give it a flavor of cell biology."

To do that, the Schwartz lab collaborated with Dirk Görlich, the director of cellular logistics at the Max Planck Institute for Multidisciplinary Sciences. Görlich is a co-senior author on the paper with MIT’s Boris Magasanik Professor of Biology Thomas Schwartz. Görlich's lab has produced concentrated droplets of the spaghetti-like proteins found inside the nuclear pore, and those droplets allow and exclude cargo the same way a nuclear pore will. In experiments, fluorescently-labeled cargo did not enter the droplets, but fluorescently-labeled cargo packaged in an HIV-1 capsid was delivered. This indicated that the capsid could deliver cargo through a nuclear pore. 

Using a biophysical binding assay, the researchers also showed that the HIV-1 capsid interacts with the proteins inside the channel. Different spaghetti-like proteins are found in different channel sections, such as at the cytoplasmic side's entrance or only inside the channel; there are 10 such proteins in human cells. The capsid is a promiscuous binder — it can interact with all the spaghetti-like proteins found in the channel.

The capsid can target the nuclear pore complex even without the cell's transport receptors, indicating that it is not commandeering native transport receptors to find and enter the nuclear pore. The team used a classic assay in the nucleocytoplasmic transport field to collect this evidence: When cells are treated with digitonin, their membranes become porous. Everything in the cytoplasm will leak out of the cells, but the nuclear envelope will remain intact. Despite the absence of native proteins, the capsid was attracted to the nuclear pore complex, a behavior indicative of a nuclear transport receptor.

Although the capsid behaves like a nuclear transport receptor to penetrate the nuclear pore, it is fundamentally different. A transport receptor doesn't need to conceal material for delivery the way the capsid does to avoid detection.

These findings open new lines of inquiry for what the nuclear pore complex is capable of accommodating.

"The HIV-1 capsid is one of the largest things that we now know can go through the nuclear pore complex intact," Weiskopf says. "It raises all kinds of questions — what other things could be going through the pore that we thought was impossible?"

Schwartz said another question is whether all of the 2,000 nuclear pores in human cells are identical or whether there is something that makes certain pores more amenable to allowing the capsid through.

The capsid is also known to be unusually elastic, a property that may be key for passage through the pore. Another interesting question for the field is whether the cone-shaped capsid gains entry into the pore by squeezing through.

Although the team has shown that the capsid can enter the pore, what happens at the other end of the channel is still unknown — whether the capsid fully or partially enters the nucleus or breaks down inside the channel. Weiskopf is working on perturbing parts of the capsid or the spaghetti-like proteins to learn more about which interactions are most important for successful capsid entry.

Although these results have expanded our understanding of the nuclear pore, much remains unknown, both for HIV-1 infection and for the transport process through the nuclear pore complex.  

"The nuclear pore is such an important element of cell biology, we thought it would be interesting to understand it better — and that's how we figured out that the pore is much bigger than we anticipated," Schwartz says. "We will certainly try to see whether we can understand the mechanism of HIV-1 infection, how the capsid is released on the other side of the channel, and what factors are important there — and to what extent you can manipulate it or influence it for therapeutic applications."

This research was carried out, in part, using MIT.nano facilities.

An MIT research team led by Professor Darrell Irvine has developed a novel kind of vaccine adjuvant: a nanoparticle that can help to stimulate the immune system to generate a stronger response to a vaccine. These nanoparticles contain saponin, a compound derived from the bark of the Chilean soapbark tree, along with a molecule called MPLA, each of which helps to activate the immune system.

The adjuvant has been incorporated into an experimental HIV vaccine that has shown promising results in animal studies, and this month, the first human volunteers will receive the vaccine as part of a phase 1 clinical trial run by the Consortium for HIV/AIDS Vaccine Development at the Scripps Research Institute. MIT News spoke with Irvine about why this project required an interdisciplinary approach, and what may lie ahead.

Q: What are the special features of the new nanoparticle adjuvant that help it create a more powerful immune response to vaccination? 

A: Most vaccines, such as the Covid-19 vaccines, are thought to protect us through B cells making protective antibodies. Development of an HIV vaccine has been made challenging by the fact that the B cells that are capable of evolving to produce protective antibodies — called broadly neutralizing antibodies — are very rare in the average person. Vaccine adjuvants are important in this scenario to ensure that when we immunize with an HIV antigen, these rare B cells become activated and get a chance to participate in the immune response.

We particularly discovered that this new adjuvant, which we call SMNP (short for saponin/MPLA nanoparticles), is particularly good at helping more B cells enter germinal centers, the specialized location in lymph nodes where high affinity antibodies are produced. In animal models, SMNP also has shown unique mechanisms of action: Administering antigens with SMNP leads to better antigen delivery to lymph nodes (through increases in lymph flow) and better capture of the antigen by B cells in lymph nodes.

Q: How did your lab, which generally focuses on bioengineering and materials science, end up working on HIV vaccines? What obstacles did you have to overcome in the development of this adjuvant?

A: About 15 years ago, Bruce Walker approached me about getting involved in the HIV vaccine effort, and recruited me to join the Ragon Institute of MGH, MIT, and Harvard as a member of the steering committee. Through the Ragon Institute, I met colleagues in the Scripps Consortium for HIV/AIDS Vaccine Development (CHAVD), and we realized there was a tremendous opportunity to directly contribute to the HIV vaccine challenge, working in partnership with experts in immunogen design, structural biology, and HIV pathogenesis.

As we carried out study after study of SMNP in preclinical animal models, we realized the adjuvant had really amazing effects for promoting anti-HIV antibody responses, and the CHAVD decided this was worth moving forward to testing in humans. A major challenge was transferring the technology out of the lab to synthesize large amounts of the adjuvant under GMP (good manufacturing process) conditions for a clinical trial. The initial contract manufacturing organization (CMO) hired by the consortium to produce SMNP simply couldn’t get a process to work for scalable manufacturing.

Luckily for us, a chemical engineering graduate student, Ivan Pires, whom I co-advise with Paula Hammond, head of MIT’s Department of Chemical Engineering, had developed expertise in one particular processing technique known as tangential flow filtration during his undergraduate training. Leveraging classic chemical engineering skills in thermodynamics and process design, Ivan stepped in and solved the process issues the CMO was facing, allowing the manufacturing to move forward. This to me is what makes MIT great — the ability of our students and postdocs to step up and solve big problems and make big contributions when the need arises.

Q: What other diseases could this approach be useful for? Are there any plans to test it with other types of vaccines?

A: In principle, SMNP may be helpful for any infectious disease vaccine where strong antibody responses are needed. We are currently sharing the adjuvant with about 30 different labs around the world, who are testing it in vaccines against many other pathogens including Epstein-Barr virus, malaria, and influenza. We are hopeful that if SMNP is safe and effective in humans, this will be an adjuvant that can be broadly used in infectious disease trials.

Retroviruses cannot replicate on their own — they must insert their genetic code into the DNA of a host and exploit the host cell's resources to make more copies of themselves, furthering infection. Some retroviruses only infect cells as they divide, when the nuclear envelope that protects the host's genetic material breaks down, making it easily accessible. HIV-1 is a type of retrovirus, called a lentivirus, that can infect non-dividing cells.

HIV-1 delivers its genome into the nucleus by packaging it into a large, cone-shaped structure called a capsid — but the exact mechanism has remained elusive for decades. Travel through the nuclear envelope occurs through, and is regulated by, nuclear pores, doughnut-shaped protein assemblies. Human cells have about 2,000 nuclear pores perforating the nuclear envelope. Some earlier evidence suggested that the capsid remains intact during its delivery into the nucleus — but this created a dimensional conundrum. The cone-shaped HIV-1 capsid is about 120 nanometers long and 60 nm wide — too large, researchers thought, to fit through the opening of the nuclear pore, measured at only 43 nm wide.

Members of the Schwartz Lab at MIT, in the Department of Biology, became interested in this question when a postdoc in the lab used cryo-electron tomography, slicing up sections of frozen cells to examine structures, to show that nuclear pores in the nuclear envelope are larger than 43nm. They deflate and shrink, it turns out, when removed from their native conditions. In native conditions, the nuclear pore complex is about 60nm wide — wide enough to accommodate the HIV-1 capsid.

Knowing that it could fit, a question remained: How can the capsid navigate the dense mesh of spaghetti-like proteins that act like a sieve in the nuclear pore channel? That spaghetti-like mesh allows small cargo to diffuse through, but prevents large cargo from entering unless it is escorted by proteins called nuclear transport receptors.

In an open-access paper published today in Nature, researchers present evidence that the HIV-1 capsid mimics the cell's transport receptors to traverse the nuclear pore.

To support that conclusion, the researchers showed three things in vitro: that an HIV-1 capsid can deliver cargo through a nuclear pore analog; that the capsid can interact with the sieve of proteins in the nuclear pore channel; and that the capsid targets the nuclear pore in the absence of native transport proteins.

Nuclear transport receptors escort large cargo through the nuclear pore by “batting away” the spaghetti-like mesh of proteins inside the channel — like someone holding your hand and guiding you across a crowded dance floor. The HIV-1 capsid interacts with the spaghetti-like proteins, but its purpose is more like a Trojan horse — the capsid encapsulates the viral cargo, protecting it from detection in the cytoplasm and as it enters the nuclear pore complex.

"What's really amazing about cells is that they are incredibly complex. What's really difficult about studying cells is that they are incredibly complex," jokes co-first author Erika Weiskopf, a graduate student in the Schwartz lab. "Biochemists are constantly trying to find ways to study their system in a simplified context, but still give it a flavor of cell biology."

To do that, the Schwartz lab collaborated with Dirk Görlich, the director of cellular logistics at the Max Planck Institute for Multidisciplinary Sciences. Görlich is a co-senior author on the paper with MIT’s Boris Magasanik Professor of Biology Thomas Schwartz. Görlich's lab has produced concentrated droplets of the spaghetti-like proteins found inside the nuclear pore, and those droplets allow and exclude cargo the same way a nuclear pore will. In experiments, fluorescently-labeled cargo did not enter the droplets, but fluorescently-labeled cargo packaged in an HIV-1 capsid was delivered. This indicated that the capsid could deliver cargo through a nuclear pore. 

Using a biophysical binding assay, the researchers also showed that the HIV-1 capsid interacts with the proteins inside the channel. Different spaghetti-like proteins are found in different channel sections, such as at the cytoplasmic side's entrance or only inside the channel; there are 10 such proteins in human cells. The capsid is a promiscuous binder — it can interact with all the spaghetti-like proteins found in the channel.

The capsid can target the nuclear pore complex even without the cell's transport receptors, indicating that it is not commandeering native transport receptors to find and enter the nuclear pore. The team used a classic assay in the nucleocytoplasmic transport field to collect this evidence: When cells are treated with digitonin, their membranes become porous. Everything in the cytoplasm will leak out of the cells, but the nuclear envelope will remain intact. Despite the absence of native proteins, the capsid was attracted to the nuclear pore complex, a behavior indicative of a nuclear transport receptor.

Although the capsid behaves like a nuclear transport receptor to penetrate the nuclear pore, it is fundamentally different. A transport receptor doesn't need to conceal material for delivery the way the capsid does to avoid detection.

These findings open new lines of inquiry for what the nuclear pore complex is capable of accommodating.

"The HIV-1 capsid is one of the largest things that we now know can go through the nuclear pore complex intact," Weiskopf says. "It raises all kinds of questions — what other things could be going through the pore that we thought was impossible?"

Schwartz said another question is whether all of the 2,000 nuclear pores in human cells are identical or whether there is something that makes certain pores more amenable to allowing the capsid through.

The capsid is also known to be unusually elastic, a property that may be key for passage through the pore. Another interesting question for the field is whether the cone-shaped capsid gains entry into the pore by squeezing through.

Although the team has shown that the capsid can enter the pore, what happens at the other end of the channel is still unknown — whether the capsid fully or partially enters the nucleus or breaks down inside the channel. Weiskopf is working on perturbing parts of the capsid or the spaghetti-like proteins to learn more about which interactions are most important for successful capsid entry.

Although these results have expanded our understanding of the nuclear pore, much remains unknown, both for HIV-1 infection and for the transport process through the nuclear pore complex.  

"The nuclear pore is such an important element of cell biology, we thought it would be interesting to understand it better — and that's how we figured out that the pore is much bigger than we anticipated," Schwartz says. "We will certainly try to see whether we can understand the mechanism of HIV-1 infection, how the capsid is released on the other side of the channel, and what factors are important there — and to what extent you can manipulate it or influence it for therapeutic applications."

This research was carried out, in part, using MIT.nano facilities.

An MIT research team led by Professor Darrell Irvine has developed a novel kind of vaccine adjuvant: a nanoparticle that can help to stimulate the immune system to generate a stronger response to a vaccine. These nanoparticles contain saponin, a compound derived from the bark of the Chilean soapbark tree, along with a molecule called MPLA, each of which helps to activate the immune system.

The adjuvant has been incorporated into an experimental HIV vaccine that has shown promising results in animal studies, and this month, the first human volunteers will receive the vaccine as part of a phase 1 clinical trial run by the Consortium for HIV/AIDS Vaccine Development at the Scripps Research Institute. MIT News spoke with Irvine about why this project required an interdisciplinary approach, and what may lie ahead.

Q: What are the special features of the new nanoparticle adjuvant that help it create a more powerful immune response to vaccination? 

A: Most vaccines, such as the Covid-19 vaccines, are thought to protect us through B cells making protective antibodies. Development of an HIV vaccine has been made challenging by the fact that the B cells that are capable of evolving to produce protective antibodies — called broadly neutralizing antibodies — are very rare in the average person. Vaccine adjuvants are important in this scenario to ensure that when we immunize with an HIV antigen, these rare B cells become activated and get a chance to participate in the immune response.

We particularly discovered that this new adjuvant, which we call SMNP (short for saponin/MPLA nanoparticles), is particularly good at helping more B cells enter germinal centers, the specialized location in lymph nodes where high affinity antibodies are produced. In animal models, SMNP also has shown unique mechanisms of action: Administering antigens with SMNP leads to better antigen delivery to lymph nodes (through increases in lymph flow) and better capture of the antigen by B cells in lymph nodes.

Q: How did your lab, which generally focuses on bioengineering and materials science, end up working on HIV vaccines? What obstacles did you have to overcome in the development of this adjuvant?

A: About 15 years ago, Bruce Walker approached me about getting involved in the HIV vaccine effort, and recruited me to join the Ragon Institute of MGH, MIT, and Harvard as a member of the steering committee. Through the Ragon Institute, I met colleagues in the Scripps Consortium for HIV/AIDS Vaccine Development (CHAVD), and we realized there was a tremendous opportunity to directly contribute to the HIV vaccine challenge, working in partnership with experts in immunogen design, structural biology, and HIV pathogenesis.

As we carried out study after study of SMNP in preclinical animal models, we realized the adjuvant had really amazing effects for promoting anti-HIV antibody responses, and the CHAVD decided this was worth moving forward to testing in humans. A major challenge was transferring the technology out of the lab to synthesize large amounts of the adjuvant under GMP (good manufacturing process) conditions for a clinical trial. The initial contract manufacturing organization (CMO) hired by the consortium to produce SMNP simply couldn’t get a process to work for scalable manufacturing.

Luckily for us, a chemical engineering graduate student, Ivan Pires, whom I co-advise with Paula Hammond, head of MIT’s Department of Chemical Engineering, had developed expertise in one particular processing technique known as tangential flow filtration during his undergraduate training. Leveraging classic chemical engineering skills in thermodynamics and process design, Ivan stepped in and solved the process issues the CMO was facing, allowing the manufacturing to move forward. This to me is what makes MIT great — the ability of our students and postdocs to step up and solve big problems and make big contributions when the need arises.

Q: What other diseases could this approach be useful for? Are there any plans to test it with other types of vaccines?

A: In principle, SMNP may be helpful for any infectious disease vaccine where strong antibody responses are needed. We are currently sharing the adjuvant with about 30 different labs around the world, who are testing it in vaccines against many other pathogens including Epstein-Barr virus, malaria, and influenza. We are hopeful that if SMNP is safe and effective in humans, this will be an adjuvant that can be broadly used in infectious disease trials.

Retroviruses cannot replicate on their own — they must insert their genetic code into the DNA of a host and exploit the host cell's resources to make more copies of themselves, furthering infection. Some retroviruses only infect cells as they divide, when the nuclear envelope that protects the host's genetic material breaks down, making it easily accessible. HIV-1 is a type of retrovirus, called a lentivirus, that can infect non-dividing cells.

HIV-1 delivers its genome into the nucleus by packaging it into a large, cone-shaped structure called a capsid — but the exact mechanism has remained elusive for decades. Travel through the nuclear envelope occurs through, and is regulated by, nuclear pores, doughnut-shaped protein assemblies. Human cells have about 2,000 nuclear pores perforating the nuclear envelope. Some earlier evidence suggested that the capsid remains intact during its delivery into the nucleus — but this created a dimensional conundrum. The cone-shaped HIV-1 capsid is about 120 nanometers long and 60 nm wide — too large, researchers thought, to fit through the opening of the nuclear pore, measured at only 43 nm wide.

Members of the Schwartz Lab at MIT, in the Department of Biology, became interested in this question when a postdoc in the lab used cryo-electron tomography, slicing up sections of frozen cells to examine structures, to show that nuclear pores in the nuclear envelope are larger than 43nm. They deflate and shrink, it turns out, when removed from their native conditions. In native conditions, the nuclear pore complex is about 60nm wide — wide enough to accommodate the HIV-1 capsid.

Knowing that it could fit, a question remained: How can the capsid navigate the dense mesh of spaghetti-like proteins that act like a sieve in the nuclear pore channel? That spaghetti-like mesh allows small cargo to diffuse through, but prevents large cargo from entering unless it is escorted by proteins called nuclear transport receptors.

In an open-access paper published today in Nature, researchers present evidence that the HIV-1 capsid mimics the cell's transport receptors to traverse the nuclear pore.

To support that conclusion, the researchers showed three things in vitro: that an HIV-1 capsid can deliver cargo through a nuclear pore analog; that the capsid can interact with the sieve of proteins in the nuclear pore channel; and that the capsid targets the nuclear pore in the absence of native transport proteins.

Nuclear transport receptors escort large cargo through the nuclear pore by “batting away” the spaghetti-like mesh of proteins inside the channel — like someone holding your hand and guiding you across a crowded dance floor. The HIV-1 capsid interacts with the spaghetti-like proteins, but its purpose is more like a Trojan horse — the capsid encapsulates the viral cargo, protecting it from detection in the cytoplasm and as it enters the nuclear pore complex.

"What's really amazing about cells is that they are incredibly complex. What's really difficult about studying cells is that they are incredibly complex," jokes co-first author Erika Weiskopf, a graduate student in the Schwartz lab. "Biochemists are constantly trying to find ways to study their system in a simplified context, but still give it a flavor of cell biology."

To do that, the Schwartz lab collaborated with Dirk Görlich, the director of cellular logistics at the Max Planck Institute for Multidisciplinary Sciences. Görlich is a co-senior author on the paper with MIT’s Boris Magasanik Professor of Biology Thomas Schwartz. Görlich's lab has produced concentrated droplets of the spaghetti-like proteins found inside the nuclear pore, and those droplets allow and exclude cargo the same way a nuclear pore will. In experiments, fluorescently-labeled cargo did not enter the droplets, but fluorescently-labeled cargo packaged in an HIV-1 capsid was delivered. This indicated that the capsid could deliver cargo through a nuclear pore. 

Using a biophysical binding assay, the researchers also showed that the HIV-1 capsid interacts with the proteins inside the channel. Different spaghetti-like proteins are found in different channel sections, such as at the cytoplasmic side's entrance or only inside the channel; there are 10 such proteins in human cells. The capsid is a promiscuous binder — it can interact with all the spaghetti-like proteins found in the channel.

The capsid can target the nuclear pore complex even without the cell's transport receptors, indicating that it is not commandeering native transport receptors to find and enter the nuclear pore. The team used a classic assay in the nucleocytoplasmic transport field to collect this evidence: When cells are treated with digitonin, their membranes become porous. Everything in the cytoplasm will leak out of the cells, but the nuclear envelope will remain intact. Despite the absence of native proteins, the capsid was attracted to the nuclear pore complex, a behavior indicative of a nuclear transport receptor.

Although the capsid behaves like a nuclear transport receptor to penetrate the nuclear pore, it is fundamentally different. A transport receptor doesn't need to conceal material for delivery the way the capsid does to avoid detection.

These findings open new lines of inquiry for what the nuclear pore complex is capable of accommodating.

"The HIV-1 capsid is one of the largest things that we now know can go through the nuclear pore complex intact," Weiskopf says. "It raises all kinds of questions — what other things could be going through the pore that we thought was impossible?"

Schwartz said another question is whether all of the 2,000 nuclear pores in human cells are identical or whether there is something that makes certain pores more amenable to allowing the capsid through.

The capsid is also known to be unusually elastic, a property that may be key for passage through the pore. Another interesting question for the field is whether the cone-shaped capsid gains entry into the pore by squeezing through.

Although the team has shown that the capsid can enter the pore, what happens at the other end of the channel is still unknown — whether the capsid fully or partially enters the nucleus or breaks down inside the channel. Weiskopf is working on perturbing parts of the capsid or the spaghetti-like proteins to learn more about which interactions are most important for successful capsid entry.

Although these results have expanded our understanding of the nuclear pore, much remains unknown, both for HIV-1 infection and for the transport process through the nuclear pore complex.  

"The nuclear pore is such an important element of cell biology, we thought it would be interesting to understand it better — and that's how we figured out that the pore is much bigger than we anticipated," Schwartz says. "We will certainly try to see whether we can understand the mechanism of HIV-1 infection, how the capsid is released on the other side of the channel, and what factors are important there — and to what extent you can manipulate it or influence it for therapeutic applications."

This research was carried out, in part, using MIT.nano facilities.

An MIT research team led by Professor Darrell Irvine has developed a novel kind of vaccine adjuvant: a nanoparticle that can help to stimulate the immune system to generate a stronger response to a vaccine. These nanoparticles contain saponin, a compound derived from the bark of the Chilean soapbark tree, along with a molecule called MPLA, each of which helps to activate the immune system.

The adjuvant has been incorporated into an experimental HIV vaccine that has shown promising results in animal studies, and this month, the first human volunteers will receive the vaccine as part of a phase 1 clinical trial run by the Consortium for HIV/AIDS Vaccine Development at the Scripps Research Institute. MIT News spoke with Irvine about why this project required an interdisciplinary approach, and what may lie ahead.

Q: What are the special features of the new nanoparticle adjuvant that help it create a more powerful immune response to vaccination? 

A: Most vaccines, such as the Covid-19 vaccines, are thought to protect us through B cells making protective antibodies. Development of an HIV vaccine has been made challenging by the fact that the B cells that are capable of evolving to produce protective antibodies — called broadly neutralizing antibodies — are very rare in the average person. Vaccine adjuvants are important in this scenario to ensure that when we immunize with an HIV antigen, these rare B cells become activated and get a chance to participate in the immune response.

We particularly discovered that this new adjuvant, which we call SMNP (short for saponin/MPLA nanoparticles), is particularly good at helping more B cells enter germinal centers, the specialized location in lymph nodes where high affinity antibodies are produced. In animal models, SMNP also has shown unique mechanisms of action: Administering antigens with SMNP leads to better antigen delivery to lymph nodes (through increases in lymph flow) and better capture of the antigen by B cells in lymph nodes.

Q: How did your lab, which generally focuses on bioengineering and materials science, end up working on HIV vaccines? What obstacles did you have to overcome in the development of this adjuvant?

A: About 15 years ago, Bruce Walker approached me about getting involved in the HIV vaccine effort, and recruited me to join the Ragon Institute of MGH, MIT, and Harvard as a member of the steering committee. Through the Ragon Institute, I met colleagues in the Scripps Consortium for HIV/AIDS Vaccine Development (CHAVD), and we realized there was a tremendous opportunity to directly contribute to the HIV vaccine challenge, working in partnership with experts in immunogen design, structural biology, and HIV pathogenesis.

As we carried out study after study of SMNP in preclinical animal models, we realized the adjuvant had really amazing effects for promoting anti-HIV antibody responses, and the CHAVD decided this was worth moving forward to testing in humans. A major challenge was transferring the technology out of the lab to synthesize large amounts of the adjuvant under GMP (good manufacturing process) conditions for a clinical trial. The initial contract manufacturing organization (CMO) hired by the consortium to produce SMNP simply couldn’t get a process to work for scalable manufacturing.

Luckily for us, a chemical engineering graduate student, Ivan Pires, whom I co-advise with Paula Hammond, head of MIT’s Department of Chemical Engineering, had developed expertise in one particular processing technique known as tangential flow filtration during his undergraduate training. Leveraging classic chemical engineering skills in thermodynamics and process design, Ivan stepped in and solved the process issues the CMO was facing, allowing the manufacturing to move forward. This to me is what makes MIT great — the ability of our students and postdocs to step up and solve big problems and make big contributions when the need arises.

Q: What other diseases could this approach be useful for? Are there any plans to test it with other types of vaccines?

A: In principle, SMNP may be helpful for any infectious disease vaccine where strong antibody responses are needed. We are currently sharing the adjuvant with about 30 different labs around the world, who are testing it in vaccines against many other pathogens including Epstein-Barr virus, malaria, and influenza. We are hopeful that if SMNP is safe and effective in humans, this will be an adjuvant that can be broadly used in infectious disease trials.

Retroviruses cannot replicate on their own — they must insert their genetic code into the DNA of a host and exploit the host cell's resources to make more copies of themselves, furthering infection. Some retroviruses only infect cells as they divide, when the nuclear envelope that protects the host's genetic material breaks down, making it easily accessible. HIV-1 is a type of retrovirus, called a lentivirus, that can infect non-dividing cells.

HIV-1 delivers its genome into the nucleus by packaging it into a large, cone-shaped structure called a capsid — but the exact mechanism has remained elusive for decades. Travel through the nuclear envelope occurs through, and is regulated by, nuclear pores, doughnut-shaped protein assemblies. Human cells have about 2,000 nuclear pores perforating the nuclear envelope. Some earlier evidence suggested that the capsid remains intact during its delivery into the nucleus — but this created a dimensional conundrum. The cone-shaped HIV-1 capsid is about 120 nanometers long and 60 nm wide — too large, researchers thought, to fit through the opening of the nuclear pore, measured at only 43 nm wide.

Members of the Schwartz Lab at MIT, in the Department of Biology, became interested in this question when a postdoc in the lab used cryo-electron tomography, slicing up sections of frozen cells to examine structures, to show that nuclear pores in the nuclear envelope are larger than 43nm. They deflate and shrink, it turns out, when removed from their native conditions. In native conditions, the nuclear pore complex is about 60nm wide — wide enough to accommodate the HIV-1 capsid.

Knowing that it could fit, a question remained: How can the capsid navigate the dense mesh of spaghetti-like proteins that act like a sieve in the nuclear pore channel? That spaghetti-like mesh allows small cargo to diffuse through, but prevents large cargo from entering unless it is escorted by proteins called nuclear transport receptors.

In an open-access paper published today in Nature, researchers present evidence that the HIV-1 capsid mimics the cell's transport receptors to traverse the nuclear pore.

To support that conclusion, the researchers showed three things in vitro: that an HIV-1 capsid can deliver cargo through a nuclear pore analog; that the capsid can interact with the sieve of proteins in the nuclear pore channel; and that the capsid targets the nuclear pore in the absence of native transport proteins.

Nuclear transport receptors escort large cargo through the nuclear pore by “batting away” the spaghetti-like mesh of proteins inside the channel — like someone holding your hand and guiding you across a crowded dance floor. The HIV-1 capsid interacts with the spaghetti-like proteins, but its purpose is more like a Trojan horse — the capsid encapsulates the viral cargo, protecting it from detection in the cytoplasm and as it enters the nuclear pore complex.

"What's really amazing about cells is that they are incredibly complex. What's really difficult about studying cells is that they are incredibly complex," jokes co-first author Erika Weiskopf, a graduate student in the Schwartz lab. "Biochemists are constantly trying to find ways to study their system in a simplified context, but still give it a flavor of cell biology."

To do that, the Schwartz lab collaborated with Dirk Görlich, the director of cellular logistics at the Max Planck Institute for Multidisciplinary Sciences. Görlich is a co-senior author on the paper with MIT’s Boris Magasanik Professor of Biology Thomas Schwartz. Görlich's lab has produced concentrated droplets of the spaghetti-like proteins found inside the nuclear pore, and those droplets allow and exclude cargo the same way a nuclear pore will. In experiments, fluorescently-labeled cargo did not enter the droplets, but fluorescently-labeled cargo packaged in an HIV-1 capsid was delivered. This indicated that the capsid could deliver cargo through a nuclear pore. 

Using a biophysical binding assay, the researchers also showed that the HIV-1 capsid interacts with the proteins inside the channel. Different spaghetti-like proteins are found in different channel sections, such as at the cytoplasmic side's entrance or only inside the channel; there are 10 such proteins in human cells. The capsid is a promiscuous binder — it can interact with all the spaghetti-like proteins found in the channel.

The capsid can target the nuclear pore complex even without the cell's transport receptors, indicating that it is not commandeering native transport receptors to find and enter the nuclear pore. The team used a classic assay in the nucleocytoplasmic transport field to collect this evidence: When cells are treated with digitonin, their membranes become porous. Everything in the cytoplasm will leak out of the cells, but the nuclear envelope will remain intact. Despite the absence of native proteins, the capsid was attracted to the nuclear pore complex, a behavior indicative of a nuclear transport receptor.

Although the capsid behaves like a nuclear transport receptor to penetrate the nuclear pore, it is fundamentally different. A transport receptor doesn't need to conceal material for delivery the way the capsid does to avoid detection.

These findings open new lines of inquiry for what the nuclear pore complex is capable of accommodating.

"The HIV-1 capsid is one of the largest things that we now know can go through the nuclear pore complex intact," Weiskopf says. "It raises all kinds of questions — what other things could be going through the pore that we thought was impossible?"

Schwartz said another question is whether all of the 2,000 nuclear pores in human cells are identical or whether there is something that makes certain pores more amenable to allowing the capsid through.

The capsid is also known to be unusually elastic, a property that may be key for passage through the pore. Another interesting question for the field is whether the cone-shaped capsid gains entry into the pore by squeezing through.

Although the team has shown that the capsid can enter the pore, what happens at the other end of the channel is still unknown — whether the capsid fully or partially enters the nucleus or breaks down inside the channel. Weiskopf is working on perturbing parts of the capsid or the spaghetti-like proteins to learn more about which interactions are most important for successful capsid entry.

Although these results have expanded our understanding of the nuclear pore, much remains unknown, both for HIV-1 infection and for the transport process through the nuclear pore complex.  

"The nuclear pore is such an important element of cell biology, we thought it would be interesting to understand it better — and that's how we figured out that the pore is much bigger than we anticipated," Schwartz says. "We will certainly try to see whether we can understand the mechanism of HIV-1 infection, how the capsid is released on the other side of the channel, and what factors are important there — and to what extent you can manipulate it or influence it for therapeutic applications."

This research was carried out, in part, using MIT.nano facilities.

An MIT research team led by Professor Darrell Irvine has developed a novel kind of vaccine adjuvant: a nanoparticle that can help to stimulate the immune system to generate a stronger response to a vaccine. These nanoparticles contain saponin, a compound derived from the bark of the Chilean soapbark tree, along with a molecule called MPLA, each of which helps to activate the immune system.

The adjuvant has been incorporated into an experimental HIV vaccine that has shown promising results in animal studies, and this month, the first human volunteers will receive the vaccine as part of a phase 1 clinical trial run by the Consortium for HIV/AIDS Vaccine Development at the Scripps Research Institute. MIT News spoke with Irvine about why this project required an interdisciplinary approach, and what may lie ahead.

Q: What are the special features of the new nanoparticle adjuvant that help it create a more powerful immune response to vaccination? 

A: Most vaccines, such as the Covid-19 vaccines, are thought to protect us through B cells making protective antibodies. Development of an HIV vaccine has been made challenging by the fact that the B cells that are capable of evolving to produce protective antibodies — called broadly neutralizing antibodies — are very rare in the average person. Vaccine adjuvants are important in this scenario to ensure that when we immunize with an HIV antigen, these rare B cells become activated and get a chance to participate in the immune response.

We particularly discovered that this new adjuvant, which we call SMNP (short for saponin/MPLA nanoparticles), is particularly good at helping more B cells enter germinal centers, the specialized location in lymph nodes where high affinity antibodies are produced. In animal models, SMNP also has shown unique mechanisms of action: Administering antigens with SMNP leads to better antigen delivery to lymph nodes (through increases in lymph flow) and better capture of the antigen by B cells in lymph nodes.

Q: How did your lab, which generally focuses on bioengineering and materials science, end up working on HIV vaccines? What obstacles did you have to overcome in the development of this adjuvant?

A: About 15 years ago, Bruce Walker approached me about getting involved in the HIV vaccine effort, and recruited me to join the Ragon Institute of MGH, MIT, and Harvard as a member of the steering committee. Through the Ragon Institute, I met colleagues in the Scripps Consortium for HIV/AIDS Vaccine Development (CHAVD), and we realized there was a tremendous opportunity to directly contribute to the HIV vaccine challenge, working in partnership with experts in immunogen design, structural biology, and HIV pathogenesis.

As we carried out study after study of SMNP in preclinical animal models, we realized the adjuvant had really amazing effects for promoting anti-HIV antibody responses, and the CHAVD decided this was worth moving forward to testing in humans. A major challenge was transferring the technology out of the lab to synthesize large amounts of the adjuvant under GMP (good manufacturing process) conditions for a clinical trial. The initial contract manufacturing organization (CMO) hired by the consortium to produce SMNP simply couldn’t get a process to work for scalable manufacturing.

Luckily for us, a chemical engineering graduate student, Ivan Pires, whom I co-advise with Paula Hammond, head of MIT’s Department of Chemical Engineering, had developed expertise in one particular processing technique known as tangential flow filtration during his undergraduate training. Leveraging classic chemical engineering skills in thermodynamics and process design, Ivan stepped in and solved the process issues the CMO was facing, allowing the manufacturing to move forward. This to me is what makes MIT great — the ability of our students and postdocs to step up and solve big problems and make big contributions when the need arises.

Q: What other diseases could this approach be useful for? Are there any plans to test it with other types of vaccines?

A: In principle, SMNP may be helpful for any infectious disease vaccine where strong antibody responses are needed. We are currently sharing the adjuvant with about 30 different labs around the world, who are testing it in vaccines against many other pathogens including Epstein-Barr virus, malaria, and influenza. We are hopeful that if SMNP is safe and effective in humans, this will be an adjuvant that can be broadly used in infectious disease trials.

Retroviruses cannot replicate on their own — they must insert their genetic code into the DNA of a host and exploit the host cell's resources to make more copies of themselves, furthering infection. Some retroviruses only infect cells as they divide, when the nuclear envelope that protects the host's genetic material breaks down, making it easily accessible. HIV-1 is a type of retrovirus, called a lentivirus, that can infect non-dividing cells.

HIV-1 delivers its genome into the nucleus by packaging it into a large, cone-shaped structure called a capsid — but the exact mechanism has remained elusive for decades. Travel through the nuclear envelope occurs through, and is regulated by, nuclear pores, doughnut-shaped protein assemblies. Human cells have about 2,000 nuclear pores perforating the nuclear envelope. Some earlier evidence suggested that the capsid remains intact during its delivery into the nucleus — but this created a dimensional conundrum. The cone-shaped HIV-1 capsid is about 120 nanometers long and 60 nm wide — too large, researchers thought, to fit through the opening of the nuclear pore, measured at only 43 nm wide.

Members of the Schwartz Lab at MIT, in the Department of Biology, became interested in this question when a postdoc in the lab used cryo-electron tomography, slicing up sections of frozen cells to examine structures, to show that nuclear pores in the nuclear envelope are larger than 43nm. They deflate and shrink, it turns out, when removed from their native conditions. In native conditions, the nuclear pore complex is about 60nm wide — wide enough to accommodate the HIV-1 capsid.

Knowing that it could fit, a question remained: How can the capsid navigate the dense mesh of spaghetti-like proteins that act like a sieve in the nuclear pore channel? That spaghetti-like mesh allows small cargo to diffuse through, but prevents large cargo from entering unless it is escorted by proteins called nuclear transport receptors.

In an open-access paper published today in Nature, researchers present evidence that the HIV-1 capsid mimics the cell's transport receptors to traverse the nuclear pore.

To support that conclusion, the researchers showed three things in vitro: that an HIV-1 capsid can deliver cargo through a nuclear pore analog; that the capsid can interact with the sieve of proteins in the nuclear pore channel; and that the capsid targets the nuclear pore in the absence of native transport proteins.

Nuclear transport receptors escort large cargo through the nuclear pore by “batting away” the spaghetti-like mesh of proteins inside the channel — like someone holding your hand and guiding you across a crowded dance floor. The HIV-1 capsid interacts with the spaghetti-like proteins, but its purpose is more like a Trojan horse — the capsid encapsulates the viral cargo, protecting it from detection in the cytoplasm and as it enters the nuclear pore complex.

"What's really amazing about cells is that they are incredibly complex. What's really difficult about studying cells is that they are incredibly complex," jokes co-first author Erika Weiskopf, a graduate student in the Schwartz lab. "Biochemists are constantly trying to find ways to study their system in a simplified context, but still give it a flavor of cell biology."

To do that, the Schwartz lab collaborated with Dirk Görlich, the director of cellular logistics at the Max Planck Institute for Multidisciplinary Sciences. Görlich is a co-senior author on the paper with MIT’s Boris Magasanik Professor of Biology Thomas Schwartz. Görlich's lab has produced concentrated droplets of the spaghetti-like proteins found inside the nuclear pore, and those droplets allow and exclude cargo the same way a nuclear pore will. In experiments, fluorescently-labeled cargo did not enter the droplets, but fluorescently-labeled cargo packaged in an HIV-1 capsid was delivered. This indicated that the capsid could deliver cargo through a nuclear pore. 

Using a biophysical binding assay, the researchers also showed that the HIV-1 capsid interacts with the proteins inside the channel. Different spaghetti-like proteins are found in different channel sections, such as at the cytoplasmic side's entrance or only inside the channel; there are 10 such proteins in human cells. The capsid is a promiscuous binder — it can interact with all the spaghetti-like proteins found in the channel.

The capsid can target the nuclear pore complex even without the cell's transport receptors, indicating that it is not commandeering native transport receptors to find and enter the nuclear pore. The team used a classic assay in the nucleocytoplasmic transport field to collect this evidence: When cells are treated with digitonin, their membranes become porous. Everything in the cytoplasm will leak out of the cells, but the nuclear envelope will remain intact. Despite the absence of native proteins, the capsid was attracted to the nuclear pore complex, a behavior indicative of a nuclear transport receptor.

Although the capsid behaves like a nuclear transport receptor to penetrate the nuclear pore, it is fundamentally different. A transport receptor doesn't need to conceal material for delivery the way the capsid does to avoid detection.

These findings open new lines of inquiry for what the nuclear pore complex is capable of accommodating.

"The HIV-1 capsid is one of the largest things that we now know can go through the nuclear pore complex intact," Weiskopf says. "It raises all kinds of questions — what other things could be going through the pore that we thought was impossible?"

Schwartz said another question is whether all of the 2,000 nuclear pores in human cells are identical or whether there is something that makes certain pores more amenable to allowing the capsid through.

The capsid is also known to be unusually elastic, a property that may be key for passage through the pore. Another interesting question for the field is whether the cone-shaped capsid gains entry into the pore by squeezing through.

Although the team has shown that the capsid can enter the pore, what happens at the other end of the channel is still unknown — whether the capsid fully or partially enters the nucleus or breaks down inside the channel. Weiskopf is working on perturbing parts of the capsid or the spaghetti-like proteins to learn more about which interactions are most important for successful capsid entry.

Although these results have expanded our understanding of the nuclear pore, much remains unknown, both for HIV-1 infection and for the transport process through the nuclear pore complex.  

"The nuclear pore is such an important element of cell biology, we thought it would be interesting to understand it better — and that's how we figured out that the pore is much bigger than we anticipated," Schwartz says. "We will certainly try to see whether we can understand the mechanism of HIV-1 infection, how the capsid is released on the other side of the channel, and what factors are important there — and to what extent you can manipulate it or influence it for therapeutic applications."

This research was carried out, in part, using MIT.nano facilities.

An MIT research team led by Professor Darrell Irvine has developed a novel kind of vaccine adjuvant: a nanoparticle that can help to stimulate the immune system to generate a stronger response to a vaccine. These nanoparticles contain saponin, a compound derived from the bark of the Chilean soapbark tree, along with a molecule called MPLA, each of which helps to activate the immune system.

The adjuvant has been incorporated into an experimental HIV vaccine that has shown promising results in animal studies, and this month, the first human volunteers will receive the vaccine as part of a phase 1 clinical trial run by the Consortium for HIV/AIDS Vaccine Development at the Scripps Research Institute. MIT News spoke with Irvine about why this project required an interdisciplinary approach, and what may lie ahead.

Q: What are the special features of the new nanoparticle adjuvant that help it create a more powerful immune response to vaccination? 

A: Most vaccines, such as the Covid-19 vaccines, are thought to protect us through B cells making protective antibodies. Development of an HIV vaccine has been made challenging by the fact that the B cells that are capable of evolving to produce protective antibodies — called broadly neutralizing antibodies — are very rare in the average person. Vaccine adjuvants are important in this scenario to ensure that when we immunize with an HIV antigen, these rare B cells become activated and get a chance to participate in the immune response.

We particularly discovered that this new adjuvant, which we call SMNP (short for saponin/MPLA nanoparticles), is particularly good at helping more B cells enter germinal centers, the specialized location in lymph nodes where high affinity antibodies are produced. In animal models, SMNP also has shown unique mechanisms of action: Administering antigens with SMNP leads to better antigen delivery to lymph nodes (through increases in lymph flow) and better capture of the antigen by B cells in lymph nodes.

Q: How did your lab, which generally focuses on bioengineering and materials science, end up working on HIV vaccines? What obstacles did you have to overcome in the development of this adjuvant?

A: About 15 years ago, Bruce Walker approached me about getting involved in the HIV vaccine effort, and recruited me to join the Ragon Institute of MGH, MIT, and Harvard as a member of the steering committee. Through the Ragon Institute, I met colleagues in the Scripps Consortium for HIV/AIDS Vaccine Development (CHAVD), and we realized there was a tremendous opportunity to directly contribute to the HIV vaccine challenge, working in partnership with experts in immunogen design, structural biology, and HIV pathogenesis.

As we carried out study after study of SMNP in preclinical animal models, we realized the adjuvant had really amazing effects for promoting anti-HIV antibody responses, and the CHAVD decided this was worth moving forward to testing in humans. A major challenge was transferring the technology out of the lab to synthesize large amounts of the adjuvant under GMP (good manufacturing process) conditions for a clinical trial. The initial contract manufacturing organization (CMO) hired by the consortium to produce SMNP simply couldn’t get a process to work for scalable manufacturing.

Luckily for us, a chemical engineering graduate student, Ivan Pires, whom I co-advise with Paula Hammond, head of MIT’s Department of Chemical Engineering, had developed expertise in one particular processing technique known as tangential flow filtration during his undergraduate training. Leveraging classic chemical engineering skills in thermodynamics and process design, Ivan stepped in and solved the process issues the CMO was facing, allowing the manufacturing to move forward. This to me is what makes MIT great — the ability of our students and postdocs to step up and solve big problems and make big contributions when the need arises.

Q: What other diseases could this approach be useful for? Are there any plans to test it with other types of vaccines?

A: In principle, SMNP may be helpful for any infectious disease vaccine where strong antibody responses are needed. We are currently sharing the adjuvant with about 30 different labs around the world, who are testing it in vaccines against many other pathogens including Epstein-Barr virus, malaria, and influenza. We are hopeful that if SMNP is safe and effective in humans, this will be an adjuvant that can be broadly used in infectious disease trials.

Retroviruses cannot replicate on their own — they must insert their genetic code into the DNA of a host and exploit the host cell's resources to make more copies of themselves, furthering infection. Some retroviruses only infect cells as they divide, when the nuclear envelope that protects the host's genetic material breaks down, making it easily accessible. HIV-1 is a type of retrovirus, called a lentivirus, that can infect non-dividing cells.

HIV-1 delivers its genome into the nucleus by packaging it into a large, cone-shaped structure called a capsid — but the exact mechanism has remained elusive for decades. Travel through the nuclear envelope occurs through, and is regulated by, nuclear pores, doughnut-shaped protein assemblies. Human cells have about 2,000 nuclear pores perforating the nuclear envelope. Some earlier evidence suggested that the capsid remains intact during its delivery into the nucleus — but this created a dimensional conundrum. The cone-shaped HIV-1 capsid is about 120 nanometers long and 60 nm wide — too large, researchers thought, to fit through the opening of the nuclear pore, measured at only 43 nm wide.

Members of the Schwartz Lab at MIT, in the Department of Biology, became interested in this question when a postdoc in the lab used cryo-electron tomography, slicing up sections of frozen cells to examine structures, to show that nuclear pores in the nuclear envelope are larger than 43nm. They deflate and shrink, it turns out, when removed from their native conditions. In native conditions, the nuclear pore complex is about 60nm wide — wide enough to accommodate the HIV-1 capsid.

Knowing that it could fit, a question remained: How can the capsid navigate the dense mesh of spaghetti-like proteins that act like a sieve in the nuclear pore channel? That spaghetti-like mesh allows small cargo to diffuse through, but prevents large cargo from entering unless it is escorted by proteins called nuclear transport receptors.

In an open-access paper published today in Nature, researchers present evidence that the HIV-1 capsid mimics the cell's transport receptors to traverse the nuclear pore.

To support that conclusion, the researchers showed three things in vitro: that an HIV-1 capsid can deliver cargo through a nuclear pore analog; that the capsid can interact with the sieve of proteins in the nuclear pore channel; and that the capsid targets the nuclear pore in the absence of native transport proteins.

Nuclear transport receptors escort large cargo through the nuclear pore by “batting away” the spaghetti-like mesh of proteins inside the channel — like someone holding your hand and guiding you across a crowded dance floor. The HIV-1 capsid interacts with the spaghetti-like proteins, but its purpose is more like a Trojan horse — the capsid encapsulates the viral cargo, protecting it from detection in the cytoplasm and as it enters the nuclear pore complex.

"What's really amazing about cells is that they are incredibly complex. What's really difficult about studying cells is that they are incredibly complex," jokes co-first author Erika Weiskopf, a graduate student in the Schwartz lab. "Biochemists are constantly trying to find ways to study their system in a simplified context, but still give it a flavor of cell biology."

To do that, the Schwartz lab collaborated with Dirk Görlich, the director of cellular logistics at the Max Planck Institute for Multidisciplinary Sciences. Görlich is a co-senior author on the paper with MIT’s Boris Magasanik Professor of Biology Thomas Schwartz. Görlich's lab has produced concentrated droplets of the spaghetti-like proteins found inside the nuclear pore, and those droplets allow and exclude cargo the same way a nuclear pore will. In experiments, fluorescently-labeled cargo did not enter the droplets, but fluorescently-labeled cargo packaged in an HIV-1 capsid was delivered. This indicated that the capsid could deliver cargo through a nuclear pore. 

Using a biophysical binding assay, the researchers also showed that the HIV-1 capsid interacts with the proteins inside the channel. Different spaghetti-like proteins are found in different channel sections, such as at the cytoplasmic side's entrance or only inside the channel; there are 10 such proteins in human cells. The capsid is a promiscuous binder — it can interact with all the spaghetti-like proteins found in the channel.

The capsid can target the nuclear pore complex even without the cell's transport receptors, indicating that it is not commandeering native transport receptors to find and enter the nuclear pore. The team used a classic assay in the nucleocytoplasmic transport field to collect this evidence: When cells are treated with digitonin, their membranes become porous. Everything in the cytoplasm will leak out of the cells, but the nuclear envelope will remain intact. Despite the absence of native proteins, the capsid was attracted to the nuclear pore complex, a behavior indicative of a nuclear transport receptor.

Although the capsid behaves like a nuclear transport receptor to penetrate the nuclear pore, it is fundamentally different. A transport receptor doesn't need to conceal material for delivery the way the capsid does to avoid detection.

These findings open new lines of inquiry for what the nuclear pore complex is capable of accommodating.

"The HIV-1 capsid is one of the largest things that we now know can go through the nuclear pore complex intact," Weiskopf says. "It raises all kinds of questions — what other things could be going through the pore that we thought was impossible?"

Schwartz said another question is whether all of the 2,000 nuclear pores in human cells are identical or whether there is something that makes certain pores more amenable to allowing the capsid through.

The capsid is also known to be unusually elastic, a property that may be key for passage through the pore. Another interesting question for the field is whether the cone-shaped capsid gains entry into the pore by squeezing through.

Although the team has shown that the capsid can enter the pore, what happens at the other end of the channel is still unknown — whether the capsid fully or partially enters the nucleus or breaks down inside the channel. Weiskopf is working on perturbing parts of the capsid or the spaghetti-like proteins to learn more about which interactions are most important for successful capsid entry.

Although these results have expanded our understanding of the nuclear pore, much remains unknown, both for HIV-1 infection and for the transport process through the nuclear pore complex.  

"The nuclear pore is such an important element of cell biology, we thought it would be interesting to understand it better — and that's how we figured out that the pore is much bigger than we anticipated," Schwartz says. "We will certainly try to see whether we can understand the mechanism of HIV-1 infection, how the capsid is released on the other side of the channel, and what factors are important there — and to what extent you can manipulate it or influence it for therapeutic applications."

This research was carried out, in part, using MIT.nano facilities.

An MIT research team led by Professor Darrell Irvine has developed a novel kind of vaccine adjuvant: a nanoparticle that can help to stimulate the immune system to generate a stronger response to a vaccine. These nanoparticles contain saponin, a compound derived from the bark of the Chilean soapbark tree, along with a molecule called MPLA, each of which helps to activate the immune system.

The adjuvant has been incorporated into an experimental HIV vaccine that has shown promising results in animal studies, and this month, the first human volunteers will receive the vaccine as part of a phase 1 clinical trial run by the Consortium for HIV/AIDS Vaccine Development at the Scripps Research Institute. MIT News spoke with Irvine about why this project required an interdisciplinary approach, and what may lie ahead.

Q: What are the special features of the new nanoparticle adjuvant that help it create a more powerful immune response to vaccination? 

A: Most vaccines, such as the Covid-19 vaccines, are thought to protect us through B cells making protective antibodies. Development of an HIV vaccine has been made challenging by the fact that the B cells that are capable of evolving to produce protective antibodies — called broadly neutralizing antibodies — are very rare in the average person. Vaccine adjuvants are important in this scenario to ensure that when we immunize with an HIV antigen, these rare B cells become activated and get a chance to participate in the immune response.

We particularly discovered that this new adjuvant, which we call SMNP (short for saponin/MPLA nanoparticles), is particularly good at helping more B cells enter germinal centers, the specialized location in lymph nodes where high affinity antibodies are produced. In animal models, SMNP also has shown unique mechanisms of action: Administering antigens with SMNP leads to better antigen delivery to lymph nodes (through increases in lymph flow) and better capture of the antigen by B cells in lymph nodes.

Q: How did your lab, which generally focuses on bioengineering and materials science, end up working on HIV vaccines? What obstacles did you have to overcome in the development of this adjuvant?

A: About 15 years ago, Bruce Walker approached me about getting involved in the HIV vaccine effort, and recruited me to join the Ragon Institute of MGH, MIT, and Harvard as a member of the steering committee. Through the Ragon Institute, I met colleagues in the Scripps Consortium for HIV/AIDS Vaccine Development (CHAVD), and we realized there was a tremendous opportunity to directly contribute to the HIV vaccine challenge, working in partnership with experts in immunogen design, structural biology, and HIV pathogenesis.

As we carried out study after study of SMNP in preclinical animal models, we realized the adjuvant had really amazing effects for promoting anti-HIV antibody responses, and the CHAVD decided this was worth moving forward to testing in humans. A major challenge was transferring the technology out of the lab to synthesize large amounts of the adjuvant under GMP (good manufacturing process) conditions for a clinical trial. The initial contract manufacturing organization (CMO) hired by the consortium to produce SMNP simply couldn’t get a process to work for scalable manufacturing.

Luckily for us, a chemical engineering graduate student, Ivan Pires, whom I co-advise with Paula Hammond, head of MIT’s Department of Chemical Engineering, had developed expertise in one particular processing technique known as tangential flow filtration during his undergraduate training. Leveraging classic chemical engineering skills in thermodynamics and process design, Ivan stepped in and solved the process issues the CMO was facing, allowing the manufacturing to move forward. This to me is what makes MIT great — the ability of our students and postdocs to step up and solve big problems and make big contributions when the need arises.

Q: What other diseases could this approach be useful for? Are there any plans to test it with other types of vaccines?

A: In principle, SMNP may be helpful for any infectious disease vaccine where strong antibody responses are needed. We are currently sharing the adjuvant with about 30 different labs around the world, who are testing it in vaccines against many other pathogens including Epstein-Barr virus, malaria, and influenza. We are hopeful that if SMNP is safe and effective in humans, this will be an adjuvant that can be broadly used in infectious disease trials.

Retroviruses cannot replicate on their own — they must insert their genetic code into the DNA of a host and exploit the host cell's resources to make more copies of themselves, furthering infection. Some retroviruses only infect cells as they divide, when the nuclear envelope that protects the host's genetic material breaks down, making it easily accessible. HIV-1 is a type of retrovirus, called a lentivirus, that can infect non-dividing cells.

HIV-1 delivers its genome into the nucleus by packaging it into a large, cone-shaped structure called a capsid — but the exact mechanism has remained elusive for decades. Travel through the nuclear envelope occurs through, and is regulated by, nuclear pores, doughnut-shaped protein assemblies. Human cells have about 2,000 nuclear pores perforating the nuclear envelope. Some earlier evidence suggested that the capsid remains intact during its delivery into the nucleus — but this created a dimensional conundrum. The cone-shaped HIV-1 capsid is about 120 nanometers long and 60 nm wide — too large, researchers thought, to fit through the opening of the nuclear pore, measured at only 43 nm wide.

Members of the Schwartz Lab at MIT, in the Department of Biology, became interested in this question when a postdoc in the lab used cryo-electron tomography, slicing up sections of frozen cells to examine structures, to show that nuclear pores in the nuclear envelope are larger than 43nm. They deflate and shrink, it turns out, when removed from their native conditions. In native conditions, the nuclear pore complex is about 60nm wide — wide enough to accommodate the HIV-1 capsid.

Knowing that it could fit, a question remained: How can the capsid navigate the dense mesh of spaghetti-like proteins that act like a sieve in the nuclear pore channel? That spaghetti-like mesh allows small cargo to diffuse through, but prevents large cargo from entering unless it is escorted by proteins called nuclear transport receptors.

In an open-access paper published today in Nature, researchers present evidence that the HIV-1 capsid mimics the cell's transport receptors to traverse the nuclear pore.

To support that conclusion, the researchers showed three things in vitro: that an HIV-1 capsid can deliver cargo through a nuclear pore analog; that the capsid can interact with the sieve of proteins in the nuclear pore channel; and that the capsid targets the nuclear pore in the absence of native transport proteins.

Nuclear transport receptors escort large cargo through the nuclear pore by “batting away” the spaghetti-like mesh of proteins inside the channel — like someone holding your hand and guiding you across a crowded dance floor. The HIV-1 capsid interacts with the spaghetti-like proteins, but its purpose is more like a Trojan horse — the capsid encapsulates the viral cargo, protecting it from detection in the cytoplasm and as it enters the nuclear pore complex.

"What's really amazing about cells is that they are incredibly complex. What's really difficult about studying cells is that they are incredibly complex," jokes co-first author Erika Weiskopf, a graduate student in the Schwartz lab. "Biochemists are constantly trying to find ways to study their system in a simplified context, but still give it a flavor of cell biology."

To do that, the Schwartz lab collaborated with Dirk Görlich, the director of cellular logistics at the Max Planck Institute for Multidisciplinary Sciences. Görlich is a co-senior author on the paper with MIT’s Boris Magasanik Professor of Biology Thomas Schwartz. Görlich's lab has produced concentrated droplets of the spaghetti-like proteins found inside the nuclear pore, and those droplets allow and exclude cargo the same way a nuclear pore will. In experiments, fluorescently-labeled cargo did not enter the droplets, but fluorescently-labeled cargo packaged in an HIV-1 capsid was delivered. This indicated that the capsid could deliver cargo through a nuclear pore. 

Using a biophysical binding assay, the researchers also showed that the HIV-1 capsid interacts with the proteins inside the channel. Different spaghetti-like proteins are found in different channel sections, such as at the cytoplasmic side's entrance or only inside the channel; there are 10 such proteins in human cells. The capsid is a promiscuous binder — it can interact with all the spaghetti-like proteins found in the channel.

The capsid can target the nuclear pore complex even without the cell's transport receptors, indicating that it is not commandeering native transport receptors to find and enter the nuclear pore. The team used a classic assay in the nucleocytoplasmic transport field to collect this evidence: When cells are treated with digitonin, their membranes become porous. Everything in the cytoplasm will leak out of the cells, but the nuclear envelope will remain intact. Despite the absence of native proteins, the capsid was attracted to the nuclear pore complex, a behavior indicative of a nuclear transport receptor.

Although the capsid behaves like a nuclear transport receptor to penetrate the nuclear pore, it is fundamentally different. A transport receptor doesn't need to conceal material for delivery the way the capsid does to avoid detection.

These findings open new lines of inquiry for what the nuclear pore complex is capable of accommodating.

"The HIV-1 capsid is one of the largest things that we now know can go through the nuclear pore complex intact," Weiskopf says. "It raises all kinds of questions — what other things could be going through the pore that we thought was impossible?"

Schwartz said another question is whether all of the 2,000 nuclear pores in human cells are identical or whether there is something that makes certain pores more amenable to allowing the capsid through.

The capsid is also known to be unusually elastic, a property that may be key for passage through the pore. Another interesting question for the field is whether the cone-shaped capsid gains entry into the pore by squeezing through.

Although the team has shown that the capsid can enter the pore, what happens at the other end of the channel is still unknown — whether the capsid fully or partially enters the nucleus or breaks down inside the channel. Weiskopf is working on perturbing parts of the capsid or the spaghetti-like proteins to learn more about which interactions are most important for successful capsid entry.

Although these results have expanded our understanding of the nuclear pore, much remains unknown, both for HIV-1 infection and for the transport process through the nuclear pore complex.  

"The nuclear pore is such an important element of cell biology, we thought it would be interesting to understand it better — and that's how we figured out that the pore is much bigger than we anticipated," Schwartz says. "We will certainly try to see whether we can understand the mechanism of HIV-1 infection, how the capsid is released on the other side of the channel, and what factors are important there — and to what extent you can manipulate it or influence it for therapeutic applications."

This research was carried out, in part, using MIT.nano facilities.

An MIT research team led by Professor Darrell Irvine has developed a novel kind of vaccine adjuvant: a nanoparticle that can help to stimulate the immune system to generate a stronger response to a vaccine. These nanoparticles contain saponin, a compound derived from the bark of the Chilean soapbark tree, along with a molecule called MPLA, each of which helps to activate the immune system.

The adjuvant has been incorporated into an experimental HIV vaccine that has shown promising results in animal studies, and this month, the first human volunteers will receive the vaccine as part of a phase 1 clinical trial run by the Consortium for HIV/AIDS Vaccine Development at the Scripps Research Institute. MIT News spoke with Irvine about why this project required an interdisciplinary approach, and what may lie ahead.

Q: What are the special features of the new nanoparticle adjuvant that help it create a more powerful immune response to vaccination? 

A: Most vaccines, such as the Covid-19 vaccines, are thought to protect us through B cells making protective antibodies. Development of an HIV vaccine has been made challenging by the fact that the B cells that are capable of evolving to produce protective antibodies — called broadly neutralizing antibodies — are very rare in the average person. Vaccine adjuvants are important in this scenario to ensure that when we immunize with an HIV antigen, these rare B cells become activated and get a chance to participate in the immune response.

We particularly discovered that this new adjuvant, which we call SMNP (short for saponin/MPLA nanoparticles), is particularly good at helping more B cells enter germinal centers, the specialized location in lymph nodes where high affinity antibodies are produced. In animal models, SMNP also has shown unique mechanisms of action: Administering antigens with SMNP leads to better antigen delivery to lymph nodes (through increases in lymph flow) and better capture of the antigen by B cells in lymph nodes.

Q: How did your lab, which generally focuses on bioengineering and materials science, end up working on HIV vaccines? What obstacles did you have to overcome in the development of this adjuvant?

A: About 15 years ago, Bruce Walker approached me about getting involved in the HIV vaccine effort, and recruited me to join the Ragon Institute of MGH, MIT, and Harvard as a member of the steering committee. Through the Ragon Institute, I met colleagues in the Scripps Consortium for HIV/AIDS Vaccine Development (CHAVD), and we realized there was a tremendous opportunity to directly contribute to the HIV vaccine challenge, working in partnership with experts in immunogen design, structural biology, and HIV pathogenesis.

As we carried out study after study of SMNP in preclinical animal models, we realized the adjuvant had really amazing effects for promoting anti-HIV antibody responses, and the CHAVD decided this was worth moving forward to testing in humans. A major challenge was transferring the technology out of the lab to synthesize large amounts of the adjuvant under GMP (good manufacturing process) conditions for a clinical trial. The initial contract manufacturing organization (CMO) hired by the consortium to produce SMNP simply couldn’t get a process to work for scalable manufacturing.

Luckily for us, a chemical engineering graduate student, Ivan Pires, whom I co-advise with Paula Hammond, head of MIT’s Department of Chemical Engineering, had developed expertise in one particular processing technique known as tangential flow filtration during his undergraduate training. Leveraging classic chemical engineering skills in thermodynamics and process design, Ivan stepped in and solved the process issues the CMO was facing, allowing the manufacturing to move forward. This to me is what makes MIT great — the ability of our students and postdocs to step up and solve big problems and make big contributions when the need arises.

Q: What other diseases could this approach be useful for? Are there any plans to test it with other types of vaccines?

A: In principle, SMNP may be helpful for any infectious disease vaccine where strong antibody responses are needed. We are currently sharing the adjuvant with about 30 different labs around the world, who are testing it in vaccines against many other pathogens including Epstein-Barr virus, malaria, and influenza. We are hopeful that if SMNP is safe and effective in humans, this will be an adjuvant that can be broadly used in infectious disease trials.

Retroviruses cannot replicate on their own — they must insert their genetic code into the DNA of a host and exploit the host cell's resources to make more copies of themselves, furthering infection. Some retroviruses only infect cells as they divide, when the nuclear envelope that protects the host's genetic material breaks down, making it easily accessible. HIV-1 is a type of retrovirus, called a lentivirus, that can infect non-dividing cells.

HIV-1 delivers its genome into the nucleus by packaging it into a large, cone-shaped structure called a capsid — but the exact mechanism has remained elusive for decades. Travel through the nuclear envelope occurs through, and is regulated by, nuclear pores, doughnut-shaped protein assemblies. Human cells have about 2,000 nuclear pores perforating the nuclear envelope. Some earlier evidence suggested that the capsid remains intact during its delivery into the nucleus — but this created a dimensional conundrum. The cone-shaped HIV-1 capsid is about 120 nanometers long and 60 nm wide — too large, researchers thought, to fit through the opening of the nuclear pore, measured at only 43 nm wide.

Members of the Schwartz Lab at MIT, in the Department of Biology, became interested in this question when a postdoc in the lab used cryo-electron tomography, slicing up sections of frozen cells to examine structures, to show that nuclear pores in the nuclear envelope are larger than 43nm. They deflate and shrink, it turns out, when removed from their native conditions. In native conditions, the nuclear pore complex is about 60nm wide — wide enough to accommodate the HIV-1 capsid.

Knowing that it could fit, a question remained: How can the capsid navigate the dense mesh of spaghetti-like proteins that act like a sieve in the nuclear pore channel? That spaghetti-like mesh allows small cargo to diffuse through, but prevents large cargo from entering unless it is escorted by proteins called nuclear transport receptors.

In an open-access paper published today in Nature, researchers present evidence that the HIV-1 capsid mimics the cell's transport receptors to traverse the nuclear pore.

To support that conclusion, the researchers showed three things in vitro: that an HIV-1 capsid can deliver cargo through a nuclear pore analog; that the capsid can interact with the sieve of proteins in the nuclear pore channel; and that the capsid targets the nuclear pore in the absence of native transport proteins.

Nuclear transport receptors escort large cargo through the nuclear pore by “batting away” the spaghetti-like mesh of proteins inside the channel — like someone holding your hand and guiding you across a crowded dance floor. The HIV-1 capsid interacts with the spaghetti-like proteins, but its purpose is more like a Trojan horse — the capsid encapsulates the viral cargo, protecting it from detection in the cytoplasm and as it enters the nuclear pore complex.

"What's really amazing about cells is that they are incredibly complex. What's really difficult about studying cells is that they are incredibly complex," jokes co-first author Erika Weiskopf, a graduate student in the Schwartz lab. "Biochemists are constantly trying to find ways to study their system in a simplified context, but still give it a flavor of cell biology."

To do that, the Schwartz lab collaborated with Dirk Görlich, the director of cellular logistics at the Max Planck Institute for Multidisciplinary Sciences. Görlich is a co-senior author on the paper with MIT’s Boris Magasanik Professor of Biology Thomas Schwartz. Görlich's lab has produced concentrated droplets of the spaghetti-like proteins found inside the nuclear pore, and those droplets allow and exclude cargo the same way a nuclear pore will. In experiments, fluorescently-labeled cargo did not enter the droplets, but fluorescently-labeled cargo packaged in an HIV-1 capsid was delivered. This indicated that the capsid could deliver cargo through a nuclear pore. 

Using a biophysical binding assay, the researchers also showed that the HIV-1 capsid interacts with the proteins inside the channel. Different spaghetti-like proteins are found in different channel sections, such as at the cytoplasmic side's entrance or only inside the channel; there are 10 such proteins in human cells. The capsid is a promiscuous binder — it can interact with all the spaghetti-like proteins found in the channel.

The capsid can target the nuclear pore complex even without the cell's transport receptors, indicating that it is not commandeering native transport receptors to find and enter the nuclear pore. The team used a classic assay in the nucleocytoplasmic transport field to collect this evidence: When cells are treated with digitonin, their membranes become porous. Everything in the cytoplasm will leak out of the cells, but the nuclear envelope will remain intact. Despite the absence of native proteins, the capsid was attracted to the nuclear pore complex, a behavior indicative of a nuclear transport receptor.

Although the capsid behaves like a nuclear transport receptor to penetrate the nuclear pore, it is fundamentally different. A transport receptor doesn't need to conceal material for delivery the way the capsid does to avoid detection.

These findings open new lines of inquiry for what the nuclear pore complex is capable of accommodating.

"The HIV-1 capsid is one of the largest things that we now know can go through the nuclear pore complex intact," Weiskopf says. "It raises all kinds of questions — what other things could be going through the pore that we thought was impossible?"

Schwartz said another question is whether all of the 2,000 nuclear pores in human cells are identical or whether there is something that makes certain pores more amenable to allowing the capsid through.

The capsid is also known to be unusually elastic, a property that may be key for passage through the pore. Another interesting question for the field is whether the cone-shaped capsid gains entry into the pore by squeezing through.

Although the team has shown that the capsid can enter the pore, what happens at the other end of the channel is still unknown — whether the capsid fully or partially enters the nucleus or breaks down inside the channel. Weiskopf is working on perturbing parts of the capsid or the spaghetti-like proteins to learn more about which interactions are most important for successful capsid entry.

Although these results have expanded our understanding of the nuclear pore, much remains unknown, both for HIV-1 infection and for the transport process through the nuclear pore complex.  

"The nuclear pore is such an important element of cell biology, we thought it would be interesting to understand it better — and that's how we figured out that the pore is much bigger than we anticipated," Schwartz says. "We will certainly try to see whether we can understand the mechanism of HIV-1 infection, how the capsid is released on the other side of the channel, and what factors are important there — and to what extent you can manipulate it or influence it for therapeutic applications."

This research was carried out, in part, using MIT.nano facilities.

An MIT research team led by Professor Darrell Irvine has developed a novel kind of vaccine adjuvant: a nanoparticle that can help to stimulate the immune system to generate a stronger response to a vaccine. These nanoparticles contain saponin, a compound derived from the bark of the Chilean soapbark tree, along with a molecule called MPLA, each of which helps to activate the immune system.

The adjuvant has been incorporated into an experimental HIV vaccine that has shown promising results in animal studies, and this month, the first human volunteers will receive the vaccine as part of a phase 1 clinical trial run by the Consortium for HIV/AIDS Vaccine Development at the Scripps Research Institute. MIT News spoke with Irvine about why this project required an interdisciplinary approach, and what may lie ahead.

Q: What are the special features of the new nanoparticle adjuvant that help it create a more powerful immune response to vaccination? 

A: Most vaccines, such as the Covid-19 vaccines, are thought to protect us through B cells making protective antibodies. Development of an HIV vaccine has been made challenging by the fact that the B cells that are capable of evolving to produce protective antibodies — called broadly neutralizing antibodies — are very rare in the average person. Vaccine adjuvants are important in this scenario to ensure that when we immunize with an HIV antigen, these rare B cells become activated and get a chance to participate in the immune response.

We particularly discovered that this new adjuvant, which we call SMNP (short for saponin/MPLA nanoparticles), is particularly good at helping more B cells enter germinal centers, the specialized location in lymph nodes where high affinity antibodies are produced. In animal models, SMNP also has shown unique mechanisms of action: Administering antigens with SMNP leads to better antigen delivery to lymph nodes (through increases in lymph flow) and better capture of the antigen by B cells in lymph nodes.

Q: How did your lab, which generally focuses on bioengineering and materials science, end up working on HIV vaccines? What obstacles did you have to overcome in the development of this adjuvant?

A: About 15 years ago, Bruce Walker approached me about getting involved in the HIV vaccine effort, and recruited me to join the Ragon Institute of MGH, MIT, and Harvard as a member of the steering committee. Through the Ragon Institute, I met colleagues in the Scripps Consortium for HIV/AIDS Vaccine Development (CHAVD), and we realized there was a tremendous opportunity to directly contribute to the HIV vaccine challenge, working in partnership with experts in immunogen design, structural biology, and HIV pathogenesis.

As we carried out study after study of SMNP in preclinical animal models, we realized the adjuvant had really amazing effects for promoting anti-HIV antibody responses, and the CHAVD decided this was worth moving forward to testing in humans. A major challenge was transferring the technology out of the lab to synthesize large amounts of the adjuvant under GMP (good manufacturing process) conditions for a clinical trial. The initial contract manufacturing organization (CMO) hired by the consortium to produce SMNP simply couldn’t get a process to work for scalable manufacturing.

Luckily for us, a chemical engineering graduate student, Ivan Pires, whom I co-advise with Paula Hammond, head of MIT’s Department of Chemical Engineering, had developed expertise in one particular processing technique known as tangential flow filtration during his undergraduate training. Leveraging classic chemical engineering skills in thermodynamics and process design, Ivan stepped in and solved the process issues the CMO was facing, allowing the manufacturing to move forward. This to me is what makes MIT great — the ability of our students and postdocs to step up and solve big problems and make big contributions when the need arises.

Q: What other diseases could this approach be useful for? Are there any plans to test it with other types of vaccines?

A: In principle, SMNP may be helpful for any infectious disease vaccine where strong antibody responses are needed. We are currently sharing the adjuvant with about 30 different labs around the world, who are testing it in vaccines against many other pathogens including Epstein-Barr virus, malaria, and influenza. We are hopeful that if SMNP is safe and effective in humans, this will be an adjuvant that can be broadly used in infectious disease trials.