NEWS&ANALYSIS
Overcrowding at an HIV lab has had a serendipitous effect. A postdoc who agreed to work in a space two floors below became intrigued by the work of a senior scientist who studied a different virus. The result was a collaboration that has made dazzling progress toward a badly needed vaccine against respiratory syncytial virus (RSV), a major killer of infants. In one of the first examples of its kind, postdoc Jason McLellan, Barney Graham, and colleagues from the Vaccine Research Center (VRC) at the U.S. National Institute of Allergy and Infectious Diseases in Bethesda, Maryland, used structural biology to successfully engineer an immunogen— the working heart of a vaccine. In mice at least, the carefully engineered RSV protein triggers a remarkably potent antibody response, 40 times higher than what’s needed to thwart the virus. The result, reported in this week’s issue of Science (p. 592), is a striking departure from the usual trial-and-error approach to vaccinemaking. It also shakes up the crowded f ield searching for a vaccine against RSV, which causes pneumonia and other lower respiratory tract diseases, hospitalizing an estimated 3 million-plus chil-
dren worldwide each year, killing 160,000. Virologist José Melero, whose RSV studies at the Instituto de Salud Carlos III in Madrid helped lay the groundwork for the VRC success, calls the work “a very important achievement.” The work began 5 years ago by happenstance. Peter Kwong, a structural biologist at VRC, had no place in his overstuffed fourth-floor HIV lab for McLellan, a new postdoctoral student. So McLellan (now at Dartmouth College) set up shop on the second floor, near the lab bench of Graham, an infectious disease researcher who has worked on RSV for 30 years. The two began to work together on a modest RSV project that grew into an attempt to solve a formidable challenge. Researchers had isolated potent neutralizing antibodies to RSV from infected people, but had failed to develop an immunogen that could stimulate their production. Could structural biology guide the way? RSV has a protein on its surface, known as F, that orchestrates its fusion with cells during the infection process. The flexible F protein has two distinct shapes, adopting one before fusion begins and one after it’s completed. In 2011, the team published
HIV Surface Proteins Finally Caught Going Au Naturel After nearly 2 decades of effort, researchers have artificially produced and structurally analyzed proteins that they say closely mimic those naturally appearing on the surface of HIV. Many investigators have high hopes that these “near native” versions of the proteins will usher in a new era of AIDS vaccine design, just as new insights into protein structure have invigorated the quest to develop a vaccine for respiratory syncytial virus (RSV) (see main story). In the shorter term, the three new studies—two published Near-native trimer (cryo-electron micrograph)
Non-native trimer (artist’s conception)
online this week in Science—will stoke long-standing debates about the precise shape of these proteins, which cluster into what resemble mushrooms sprouting from the viral surface, and how they stimulate an immune response to HIV. HIV infects cells via two attached surface proteins that bud through the viral membrane in groups of three, called trimers (the mushrooms). For technical reasons, membrane-bound trimers are difficult to produce in large enough quantities for fine-grained structural analysis. When researchers manufacture these proteins without the membrane anchoring them, the fragile trimers fall apart, making them impossible to study. Many groups have chosen to make specific amino acid changes so the trimers hold together, but these are far from the native form. The two Science papers describe how a structural biology team led by Ian Wilson of the Scripps Research Institute in San Diego, California, finally got highresolution portraits of the near-native trimers. Key to their success were stable, lab-made versions of the proteins, designed by immunologist John Mimicking nature. “Near-native” HIV trimers have a consistent shape (antibodies attached in gray), but non-native trimers always differ.
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SCIENCE
Published by AAAS
www.sciencemag.org
Downloaded from www.sciencemag.org on November 4, 2013
Structural Biology Triumph Offers Hope Against a Childhood Killer
the structure of postfusion F protein bound to neutralizing antibodies, hoping these data might help vaccine design. Around the same time, Melero and co-workers found evidence that the postfusion protein was not the target for most of the protective antibodies. When they eliminated antibodies that bound to postfusion F from the serum of people infected with RSV, the leftover antibodies continued to neutralize the virus. “That was puzzling, but created a great opportunity,” Kwong says. “That told us there was another type of response that could be much better than the one to postfusion F.” This spring, the VRC group reported in Science (31 May, p. 1113) that it had crystalized a potent antibody bound to the prefusion F structure, spotlighting a site on the virus that was especially vulnerable to neutralization. But the prefusion protein was unstable, making it impossible to formulate as an immunogen. So the team set out to effectively freeze the prefusion F structure, forcing it to continuously display that vulnerable site. The team stabilized the F protein into the specific shape it wanted by introducing new chemical bonds and swapping out naturally occurring amino acids for substitutes that would fill cavities in its structure. They constructed more than 100 variants of the prefusion protein, then selected a favorite that was relatively easy to produce, stable, and triggered the desired antibodies. “This
CREDIT: JONATHAN STUCKEY/VACCINE RESEARCH CENTER/NIAID/NIH CREDIT: ANDREW WARD/SCRIPPS RESEARCH INSTITUTION
VA C C I N E S
NEWS&ANALYSIS Hot spot. An antibody (black) can cripple RSV by binding to a vulnerable site (white) on its F protein.
CREDIT: CREDIT: ANDREW JONATHAN WARD/SCRIPPS STUCKEY/VACCINE RESEARCH RESEARCH INSTITUTION CENTER/NIAID/NIH
is the first time anyone has gone from antibody to vaccine and proved that it’s not just a pipe dream,” Kwong says. James Crowe, a pediatrician at Vanderbilt University Medical Center in Nashville who studies B cell responses to RSV and other viruses, says it’s impressive that they’ve effectively tamed an “ill-behaved” protein. “This is a seminal paper in terms of stabilizing a dynamic structure to increase immunogenicity,” Crowe says. He cautions, however, that safety concerns will complicate tests of this protein in infants. In a clinical trial in the mid-1960s, an RSV vaccine made from a killed version of the virus enhanced disease in children between 2 and 7 months of age, increasing hospitalization rates and leading to two deaths. The highly refined VRC protein may sidestep these problems, but Graham says they have no intention of testing it in infants. Instead, he suggests that trials should vaccinate pregnant women to test whether they produce antibodies that are then transferred to their babies, protecting them for their first few months, when they’re most vulnerable to RSV. He expects they will have a “clinical grade protein,” made by either VRC or an industrial partner, ready for human tests within 2 years. Says Graham: “There are a lot of motivated people and companies.” –JON COHEN
Moore of the Weill Medical College of Cornell University in New York City and his co-workers. “This has been on the Top 10 Most Wanted list for structural biologists,” says Peter Kwong, who does structural analyses of both HIV and RSV at the Vaccine Research Center (VRC) of the National Institute of Allergy and Infectious Diseases in Bethesda, Maryland. The new findings promise to guide attempts to devise immunogens— vaccine components—that can trigger production of so-called broadly neutralizing antibodies (bNAbs), which many immunologists believe a successful HIV vaccine needs to elicit. (Isolated from infected people, bNAbs offer them little help because they take years to appear and are made in tiny amounts.) Unlike ordinary antibodies, which the virus easily evades by mutating or which don’t have neutralizing power to begin with, bNAbs can thwart many variants of the virus (Science, 13 September, p. 1168). “It’s elegant, beautiful work,” says VRC Director John Mascola. “I think we’ll see a whole new wave of immunogen design that will come out of this.” Moore and colleagues spent 15 years attempting to create stable versions of the native trimer outside of a membrane, adding chemical bonds and removing parts of the proteins to enable them to maintain their native configuration. The result could help settle contentious debates about the trimer’s structure (Science, 2 August, p. 443). Kwong and others say the new structures are especially convincing because two different techniques—x-ray crystallography and cryo-electron microscopy—
www.sciencemag.org
SCIENCE
independently arrived at the same images. A group at the U.S. National Cancer Institute that analyzed earlier versions of the trimers used in the Science studies confirms the new structures in a 23 October online report in Nature Structural & Molecular Biology. Wilson says the sharper picture of the near-native trimers may give vaccine designers new ideas about the infection process and how to thwart it. Moore suggests that because native trimers trigger bNAbs naturally, they might work better as immunogens than the non-native trimers other researchers have been studying. Test-tube studies also show that bNAbs bind better to native trimers. “I’m not saying every bNAb ever induced must have been derived from a native trimer, but I think it’s reasonable that many of them will have been,” Moore says. Moore’s lab-made trimers have not been tested in animals, although those studies are under way. Several groups making immunogens with nonnative structures caution that just because a bNAb binds to a trimer, it doesn’t mean that trimer can teach an immune system to make the same antibody. “These two papers provide some exquisite structural biology that is very appealing, however beauty is in the eye of the beholder, and, in this respect, it’s the immune system that is the final arbiter,” says Robin Shattock, an immunologist at Imperial College London. “So in the race to induce broadly neutralizing antibodies, only time will tell whether these structures are a game changer or an incremental step.” – J. C.
VOL 342
Published by AAAS
1 NOVEMBER 2013
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Overcrowding at an HIV lab has had a serendipitous effect. A postdoc who agreed to work in a space two floors below became intrigued by the work of a senior scientist who studied a different virus. The result was a collaboration that has made dazzling progress toward a badly needed vaccine against respiratory syncytial virus (RSV), a major killer of infants. In one of the first examples of its kind, postdoc Jason McLellan, Barney Graham, and colleagues from the Vaccine Research Center (VRC) at the U.S. National Institute of Allergy and Infectious Diseases in Bethesda, Maryland, used structural biology to successfully engineer an immunogen— the working heart of a vaccine. In mice at least, the carefully engineered RSV protein triggers a remarkably potent antibody response, 40 times higher than what’s needed to thwart the virus. The result, reported in this week’s issue of Science (p. 592), is a striking departure from the usual trial-and-error approach to vaccinemaking. It also shakes up the crowded f ield searching for a vaccine against RSV, which causes pneumonia and other lower respiratory tract diseases, hospitalizing an estimated 3 million-plus chil-
dren worldwide each year, killing 160,000. Virologist José Melero, whose RSV studies at the Instituto de Salud Carlos III in Madrid helped lay the groundwork for the VRC success, calls the work “a very important achievement.” The work began 5 years ago by happenstance. Peter Kwong, a structural biologist at VRC, had no place in his overstuffed fourth-floor HIV lab for McLellan, a new postdoctoral student. So McLellan (now at Dartmouth College) set up shop on the second floor, near the lab bench of Graham, an infectious disease researcher who has worked on RSV for 30 years. The two began to work together on a modest RSV project that grew into an attempt to solve a formidable challenge. Researchers had isolated potent neutralizing antibodies to RSV from infected people, but had failed to develop an immunogen that could stimulate their production. Could structural biology guide the way? RSV has a protein on its surface, known as F, that orchestrates its fusion with cells during the infection process. The flexible F protein has two distinct shapes, adopting one before fusion begins and one after it’s completed. In 2011, the team published
HIV Surface Proteins Finally Caught Going Au Naturel After nearly 2 decades of effort, researchers have artificially produced and structurally analyzed proteins that they say closely mimic those naturally appearing on the surface of HIV. Many investigators have high hopes that these “near native” versions of the proteins will usher in a new era of AIDS vaccine design, just as new insights into protein structure have invigorated the quest to develop a vaccine for respiratory syncytial virus (RSV) (see main story). In the shorter term, the three new studies—two published Near-native trimer (cryo-electron micrograph)
Non-native trimer (artist’s conception)
online this week in Science—will stoke long-standing debates about the precise shape of these proteins, which cluster into what resemble mushrooms sprouting from the viral surface, and how they stimulate an immune response to HIV. HIV infects cells via two attached surface proteins that bud through the viral membrane in groups of three, called trimers (the mushrooms). For technical reasons, membrane-bound trimers are difficult to produce in large enough quantities for fine-grained structural analysis. When researchers manufacture these proteins without the membrane anchoring them, the fragile trimers fall apart, making them impossible to study. Many groups have chosen to make specific amino acid changes so the trimers hold together, but these are far from the native form. The two Science papers describe how a structural biology team led by Ian Wilson of the Scripps Research Institute in San Diego, California, finally got highresolution portraits of the near-native trimers. Key to their success were stable, lab-made versions of the proteins, designed by immunologist John Mimicking nature. “Near-native” HIV trimers have a consistent shape (antibodies attached in gray), but non-native trimers always differ.
546
1 NOVEMBER NO 2013
VOL 342
SCIENCE
Published by AAAS
www.sciencemag.org
Downloaded from www.sciencemag.org on November 4, 2013
Structural Biology Triumph Offers Hope Against a Childhood Killer
the structure of postfusion F protein bound to neutralizing antibodies, hoping these data might help vaccine design. Around the same time, Melero and co-workers found evidence that the postfusion protein was not the target for most of the protective antibodies. When they eliminated antibodies that bound to postfusion F from the serum of people infected with RSV, the leftover antibodies continued to neutralize the virus. “That was puzzling, but created a great opportunity,” Kwong says. “That told us there was another type of response that could be much better than the one to postfusion F.” This spring, the VRC group reported in Science (31 May, p. 1113) that it had crystalized a potent antibody bound to the prefusion F structure, spotlighting a site on the virus that was especially vulnerable to neutralization. But the prefusion protein was unstable, making it impossible to formulate as an immunogen. So the team set out to effectively freeze the prefusion F structure, forcing it to continuously display that vulnerable site. The team stabilized the F protein into the specific shape it wanted by introducing new chemical bonds and swapping out naturally occurring amino acids for substitutes that would fill cavities in its structure. They constructed more than 100 variants of the prefusion protein, then selected a favorite that was relatively easy to produce, stable, and triggered the desired antibodies. “This
CREDIT: JONATHAN STUCKEY/VACCINE RESEARCH CENTER/NIAID/NIH CREDIT: ANDREW WARD/SCRIPPS RESEARCH INSTITUTION
VA C C I N E S
NEWS&ANALYSIS Hot spot. An antibody (black) can cripple RSV by binding to a vulnerable site (white) on its F protein.
CREDIT: CREDIT: ANDREW JONATHAN WARD/SCRIPPS STUCKEY/VACCINE RESEARCH RESEARCH INSTITUTION CENTER/NIAID/NIH
is the first time anyone has gone from antibody to vaccine and proved that it’s not just a pipe dream,” Kwong says. James Crowe, a pediatrician at Vanderbilt University Medical Center in Nashville who studies B cell responses to RSV and other viruses, says it’s impressive that they’ve effectively tamed an “ill-behaved” protein. “This is a seminal paper in terms of stabilizing a dynamic structure to increase immunogenicity,” Crowe says. He cautions, however, that safety concerns will complicate tests of this protein in infants. In a clinical trial in the mid-1960s, an RSV vaccine made from a killed version of the virus enhanced disease in children between 2 and 7 months of age, increasing hospitalization rates and leading to two deaths. The highly refined VRC protein may sidestep these problems, but Graham says they have no intention of testing it in infants. Instead, he suggests that trials should vaccinate pregnant women to test whether they produce antibodies that are then transferred to their babies, protecting them for their first few months, when they’re most vulnerable to RSV. He expects they will have a “clinical grade protein,” made by either VRC or an industrial partner, ready for human tests within 2 years. Says Graham: “There are a lot of motivated people and companies.” –JON COHEN
Moore of the Weill Medical College of Cornell University in New York City and his co-workers. “This has been on the Top 10 Most Wanted list for structural biologists,” says Peter Kwong, who does structural analyses of both HIV and RSV at the Vaccine Research Center (VRC) of the National Institute of Allergy and Infectious Diseases in Bethesda, Maryland. The new findings promise to guide attempts to devise immunogens— vaccine components—that can trigger production of so-called broadly neutralizing antibodies (bNAbs), which many immunologists believe a successful HIV vaccine needs to elicit. (Isolated from infected people, bNAbs offer them little help because they take years to appear and are made in tiny amounts.) Unlike ordinary antibodies, which the virus easily evades by mutating or which don’t have neutralizing power to begin with, bNAbs can thwart many variants of the virus (Science, 13 September, p. 1168). “It’s elegant, beautiful work,” says VRC Director John Mascola. “I think we’ll see a whole new wave of immunogen design that will come out of this.” Moore and colleagues spent 15 years attempting to create stable versions of the native trimer outside of a membrane, adding chemical bonds and removing parts of the proteins to enable them to maintain their native configuration. The result could help settle contentious debates about the trimer’s structure (Science, 2 August, p. 443). Kwong and others say the new structures are especially convincing because two different techniques—x-ray crystallography and cryo-electron microscopy—
www.sciencemag.org
SCIENCE
independently arrived at the same images. A group at the U.S. National Cancer Institute that analyzed earlier versions of the trimers used in the Science studies confirms the new structures in a 23 October online report in Nature Structural & Molecular Biology. Wilson says the sharper picture of the near-native trimers may give vaccine designers new ideas about the infection process and how to thwart it. Moore suggests that because native trimers trigger bNAbs naturally, they might work better as immunogens than the non-native trimers other researchers have been studying. Test-tube studies also show that bNAbs bind better to native trimers. “I’m not saying every bNAb ever induced must have been derived from a native trimer, but I think it’s reasonable that many of them will have been,” Moore says. Moore’s lab-made trimers have not been tested in animals, although those studies are under way. Several groups making immunogens with nonnative structures caution that just because a bNAb binds to a trimer, it doesn’t mean that trimer can teach an immune system to make the same antibody. “These two papers provide some exquisite structural biology that is very appealing, however beauty is in the eye of the beholder, and, in this respect, it’s the immune system that is the final arbiter,” says Robin Shattock, an immunologist at Imperial College London. “So in the race to induce broadly neutralizing antibodies, only time will tell whether these structures are a game changer or an incremental step.” – J. C.
VOL 342
Published by AAAS
1 NOVEMBER 2013
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