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Hepatitis C Virus Neutralizing Antibodies: Is a Vaccine Still Possible?
Cell Host & Microbe
Previews Hepatitis C Virus Neutralizing Antibodies: Is a Vaccine Still Possible? Ype P. de Jong1,2,* 1Division
of Gastroenterology and Hepatology, Weill Cornell Medicine, New York, NY 10065, USA of Virology and Infectious Disease, The Rockefeller University, New York, NY 10065, USA *Correspondence: [email protected] https://doi.org/10.1016/j.chom.2018.10.017 2Laboratory
Many hurdles have plagued the development of an effective vaccine for hepatitis C virus. In this issue of Cell Host & Microbe, Kinchen et al. (2018) and Flyak et al. (2018) report on the characterization of neutralizing antibodies from individuals that spontaneously cleared infection, providing insights that promise to propel vaccine design forward. For decades, chronic hepatitis C virus (HCV) infection has been the leading cause of liver disease in the United States and many countries around the world. In 1989, the infectious agent responsible for non-A non-B hepatitis was identified by Houghton and colleagues and termed HCV. It is a member of the Flaviviridae family of RNA viruses that infects human hepatocytes, cells that make up most of the liver. Long-term chronic infection can lead to cirrhosis, which puts patients at risk for hepatocellular carcinoma and liver failure. Since its identification, much effort has been put into understanding immune responses to HCV with the goal of developing prophylactic and therapeutic vaccines (Houghton, 2011). This has led to valuable insights into innate and adaptive immune responses during acute and chronic HCV infection and established essential roles for both CD4+ and CD8+ T cells in HCV clearance (Park and Rehermann, 2014). Compared to T and NK cell functions, much less is known about the roles that B cells and neutralizing antibodies (nAbs) play in controlling HCV infection. Nevertheless, both T cell and humoral vaccine strategies have been pursued. There are several clinical observations that favor the feasibility of creating effective HCV vaccines. These include a longstanding awareness that a large subgroup of HCV exposed individuals spontaneously clears infection, which sharply contrasts to several other viruses, and most notably human immunodeficiency virus. It suggests that vaccine strategies that enhance the initial immune response may be able to prevent progression to chronic HCV infection. Further, it is widely
documented that immunodeficiencies, including B cell-depleting anti-CD20 therapies, can result in worse HCV infection outcomes. These data indicate that B cells and/or antibodies play an important role in controlling infection. In addition, some individuals who were cured of a chronic infection spontaneously cleared HCV upon reinfection, supporting the idea that effective immunological memory can be established at least in some individuals. However, there have also been many biological challenges and technical hurdles to vaccine development. The severely restricted tropism of HCV to human and chimpanzee hepatocytes has precluded immunological studies in immunocompetent rodent models and limited vaccine testing to chimpanzees. The ethical concerns and cost restrictions of working with primates have severely slowed the evaluation of various vaccine strategies. Furthermore, landmark studies showed that some chimpanzees who were cured of infection remained susceptible to reinfection by the same HCV isolate (Bukh et al., 2008). This illustrated that infection does not universally lead to the development of sterilizing immunity even to an identical HCV isolate. On the viral side, there have been ample challenges as well. The enormous diversity among HCV genotypes and intragenotypic isolates has limited the generalizability of findings. Most naturally occurring nAbs recognize a region in one of the two viral envelope (E) proteins E1 and E2. This so-called hypervariable region in E2 is the most diverse region in the HCV genome and presumably helps the virus mutate away from the nAb and T cell responses that develop during
620 Cell Host & Microbe 24, November 14, 2018 ª 2018 Elsevier Inc.
chronic infection. Finally, several technical hurdles have long hampered HCV research, with repercussions for vaccine development. The first infectious cell culture virus, which was much needed to generate tools for vaccine studies, was established only in 2005. And separately, crystallization of full-length E2 and the E1E2 heterodimer has remained challenging because of their unstable structures (Yost et al., 2018), thus limiting rational vaccine design. Despite great efforts, these and other obstacles have to this date eluded development of an effective vaccine. In this issue of Cell Host & Microbe, collaborative papers by the laboratories of Bjorkman and Bailey further characterize nAbs that were isolated from two individuals who spontaneously cleared HCV infection (Kinchen et al., 2018; Flyak et al., 2018). Although a number of nAbs had previously been isolated from chronically infected patients, the current analysis was performed on nAbs identified during acute HCV infections in those subjects. This allowed for longitudinal functional analyses of HCV quasispecies, the complex mixture of genetic variants that are present at any time in the infected individual. The clinical observational study by Kinchen et al. (2018) used state-ofthe-art technologies to study how nAbs in these two individuals drove HCV evolution toward mutations in E2. Such mutations are commonly observed under immune selection pressure, but in these individuals the pressure was broad and potent enough to force the virus toward less functional E2 epitopes that diminished its ability to enter hepatocytes. Convincing functional studies showed
Cell Host & Microbe
Previews that these nAbs were responsible for immune pressure, which presumably contributed to spontaneous clearance. In the accompanying study, Flyak et al. (2018) use the same nAbs from these two individuals to overcome a long-standing hurdle in vaccine design, namely crystallization of the E2 ectodomain. They describe how two nAbs use an unusual disulfide motif for binding to E2, something that had not been appreciated in previous crystal structures of underglycosylated and truncated E2. The new crystal structures identify a conserved epitope on E2, which, together with the study of Kinchen et al. (2018), indicates that the virus can only mutate away from the nAbs at great fitness cost. These findings have important implications for improved vaccine immunogen design. In addition to the major contributions in these two studies, other recent findings could help improve vaccine development. Efficient interruption of HCV spread during chronic infection, either by nAbs or by blocking the host entry factor claudin-1, rapidly cured immunodeficient mice with humanized livers (de Jong et al., 2014; Mailly et al., 2015). These findings suggest that a vaccine strategy that impairs HCV entry and spread may suffice to tilt the balance toward spontaneous clearance. And a newly developed immunocompetent mouse model that supports chronic infection with a rodent HCV ortholog will finally allow for highthroughput testing of vaccine strategies (Billerbeck et al., 2017). These and other
encouraging advancements have, however, largely been overshadowed by astonishing breakthroughs in clinical HCV treatment. For two decades, interferon-a-based treatments were poorly effective and highly toxic. The past 5 years have witnessed the rapid rollout of various direct-acting antiviral (DAA) combination therapies that can cure HCV-infected patients with minimal side effects. The latest DAA regimens also cure historically challenging patient populations (Vermehren et al., 2018), opening the door to speculation about eradicating HCV. Indeed, modeling studies suggest that widespread testing and DAA treatment can result in HCV eradication from parts of the world, something that just a few years ago would have been unthinkable without a vaccine. An effective HCV vaccine remains highly desirable for several populations, e.g., the rising number of intravenous drug users in the United States, and in areas with poor healthcare infrastructure. Yet after nearly three decades of scientific challenges developing such a vaccine, DAA treatment success may soon become the biggest hurdle. REFERENCES Billerbeck, E., Wolfisberg, R., Fahnøe, U., Xiao, J.W., Quirk, C., Luna, J.M., Cullen, J.M., Hartlage, A.S., Chiriboga, L., Ghoshal, K., et al. (2017). Mouse models of acute and chronic hepacivirus infection. Science 357, 204–208. Bukh, J., Thimme, R., Meunier, J.C., Faulk, K., Spangenberg, H.C., Chang, K.M., Satterfield, W.,
Chisari, F.V., and Purcell, R.H. (2008). Previously infected chimpanzees are not consistently protected against reinfection or persistent infection after reexposure to the identical hepatitis C virus strain. J. Virol. 82, 8183–8195. de Jong, Y.P., Dorner, M., Mommersteeg, M.C., Xiao, J.W., Balazs, A.B., Robbins, J.B., Winer, B.Y., Gerges, S., Vega, K., Labitt, R.N., et al. (2014). Broadly neutralizing antibodies abrogate established hepatitis C virus infection. Sci. Transl. Med. 6, 254ra129. Flyak, A.I., Ruiz, S., Colbert, M., Luong, T., Crowe, J.E., Jr., Bailey, J.R., and Bjorkman, P.J. (2018). Broadly neutralizing antibodies against HCV use a CDRH3 disulfide motif to recognize an E2 glycoprotein site that can be targeted for vaccine design. Cell Host Microbe 24, this issue, 703–716. Houghton, M. (2011). Prospects for prophylactic and therapeutic vaccines against the hepatitis C viruses. Immunol. Rev. 239, 99–108. Kinchen, V.J., Zahid, M.N., Flyak, A.I., Soliman, M.G., Learn, G.H., Wang, S., Davidson, E., Doranz, B.J., Ray, S.C., Cox, A.L., et al. (2018). Broadly neutralizing antibody mediated clearance of human hepatitis C virus infection. Cell Host Microbe 24, this issue, 717–730. Mailly, L., Xiao, F., Lupberger, J., Wilson, G.K., Aubert, P., Duong, F.H.T., Calabrese, D., Leboeuf, C., Fofana, I., Thumann, C., et al. (2015). Clearance of persistent hepatitis C virus infection in humanized mice using a claudin-1-targeting monoclonal antibody. Nat. Biotechnol. 33, 549–554. Park, S.H., and Rehermann, B. (2014). Immune responses to HCV and other hepatitis viruses. Immunity 40, 13–24. Vermehren, J., Park, J.S., Jacobson, I.M., and Zeuzem, S. (2018). Challenges and perspectives of direct antivirals for the treatment of hepatitis C virus infection. J. Hepatol. 69, 1178–1187. Yost, S.A., Wang, Y., and Marcotrigiano, J. (2018). Hepatitis C virus envelope glycoproteins: a balancing act of order and disorder. Front. Immunol. 9, 1917.
Cell Host & Microbe 24, November 14, 2018 621
Previews Hepatitis C Virus Neutralizing Antibodies: Is a Vaccine Still Possible? Ype P. de Jong1,2,* 1Division
of Gastroenterology and Hepatology, Weill Cornell Medicine, New York, NY 10065, USA of Virology and Infectious Disease, The Rockefeller University, New York, NY 10065, USA *Correspondence: [email protected] https://doi.org/10.1016/j.chom.2018.10.017 2Laboratory
Many hurdles have plagued the development of an effective vaccine for hepatitis C virus. In this issue of Cell Host & Microbe, Kinchen et al. (2018) and Flyak et al. (2018) report on the characterization of neutralizing antibodies from individuals that spontaneously cleared infection, providing insights that promise to propel vaccine design forward. For decades, chronic hepatitis C virus (HCV) infection has been the leading cause of liver disease in the United States and many countries around the world. In 1989, the infectious agent responsible for non-A non-B hepatitis was identified by Houghton and colleagues and termed HCV. It is a member of the Flaviviridae family of RNA viruses that infects human hepatocytes, cells that make up most of the liver. Long-term chronic infection can lead to cirrhosis, which puts patients at risk for hepatocellular carcinoma and liver failure. Since its identification, much effort has been put into understanding immune responses to HCV with the goal of developing prophylactic and therapeutic vaccines (Houghton, 2011). This has led to valuable insights into innate and adaptive immune responses during acute and chronic HCV infection and established essential roles for both CD4+ and CD8+ T cells in HCV clearance (Park and Rehermann, 2014). Compared to T and NK cell functions, much less is known about the roles that B cells and neutralizing antibodies (nAbs) play in controlling HCV infection. Nevertheless, both T cell and humoral vaccine strategies have been pursued. There are several clinical observations that favor the feasibility of creating effective HCV vaccines. These include a longstanding awareness that a large subgroup of HCV exposed individuals spontaneously clears infection, which sharply contrasts to several other viruses, and most notably human immunodeficiency virus. It suggests that vaccine strategies that enhance the initial immune response may be able to prevent progression to chronic HCV infection. Further, it is widely
documented that immunodeficiencies, including B cell-depleting anti-CD20 therapies, can result in worse HCV infection outcomes. These data indicate that B cells and/or antibodies play an important role in controlling infection. In addition, some individuals who were cured of a chronic infection spontaneously cleared HCV upon reinfection, supporting the idea that effective immunological memory can be established at least in some individuals. However, there have also been many biological challenges and technical hurdles to vaccine development. The severely restricted tropism of HCV to human and chimpanzee hepatocytes has precluded immunological studies in immunocompetent rodent models and limited vaccine testing to chimpanzees. The ethical concerns and cost restrictions of working with primates have severely slowed the evaluation of various vaccine strategies. Furthermore, landmark studies showed that some chimpanzees who were cured of infection remained susceptible to reinfection by the same HCV isolate (Bukh et al., 2008). This illustrated that infection does not universally lead to the development of sterilizing immunity even to an identical HCV isolate. On the viral side, there have been ample challenges as well. The enormous diversity among HCV genotypes and intragenotypic isolates has limited the generalizability of findings. Most naturally occurring nAbs recognize a region in one of the two viral envelope (E) proteins E1 and E2. This so-called hypervariable region in E2 is the most diverse region in the HCV genome and presumably helps the virus mutate away from the nAb and T cell responses that develop during
620 Cell Host & Microbe 24, November 14, 2018 ª 2018 Elsevier Inc.
chronic infection. Finally, several technical hurdles have long hampered HCV research, with repercussions for vaccine development. The first infectious cell culture virus, which was much needed to generate tools for vaccine studies, was established only in 2005. And separately, crystallization of full-length E2 and the E1E2 heterodimer has remained challenging because of their unstable structures (Yost et al., 2018), thus limiting rational vaccine design. Despite great efforts, these and other obstacles have to this date eluded development of an effective vaccine. In this issue of Cell Host & Microbe, collaborative papers by the laboratories of Bjorkman and Bailey further characterize nAbs that were isolated from two individuals who spontaneously cleared HCV infection (Kinchen et al., 2018; Flyak et al., 2018). Although a number of nAbs had previously been isolated from chronically infected patients, the current analysis was performed on nAbs identified during acute HCV infections in those subjects. This allowed for longitudinal functional analyses of HCV quasispecies, the complex mixture of genetic variants that are present at any time in the infected individual. The clinical observational study by Kinchen et al. (2018) used state-ofthe-art technologies to study how nAbs in these two individuals drove HCV evolution toward mutations in E2. Such mutations are commonly observed under immune selection pressure, but in these individuals the pressure was broad and potent enough to force the virus toward less functional E2 epitopes that diminished its ability to enter hepatocytes. Convincing functional studies showed
Cell Host & Microbe
Previews that these nAbs were responsible for immune pressure, which presumably contributed to spontaneous clearance. In the accompanying study, Flyak et al. (2018) use the same nAbs from these two individuals to overcome a long-standing hurdle in vaccine design, namely crystallization of the E2 ectodomain. They describe how two nAbs use an unusual disulfide motif for binding to E2, something that had not been appreciated in previous crystal structures of underglycosylated and truncated E2. The new crystal structures identify a conserved epitope on E2, which, together with the study of Kinchen et al. (2018), indicates that the virus can only mutate away from the nAbs at great fitness cost. These findings have important implications for improved vaccine immunogen design. In addition to the major contributions in these two studies, other recent findings could help improve vaccine development. Efficient interruption of HCV spread during chronic infection, either by nAbs or by blocking the host entry factor claudin-1, rapidly cured immunodeficient mice with humanized livers (de Jong et al., 2014; Mailly et al., 2015). These findings suggest that a vaccine strategy that impairs HCV entry and spread may suffice to tilt the balance toward spontaneous clearance. And a newly developed immunocompetent mouse model that supports chronic infection with a rodent HCV ortholog will finally allow for highthroughput testing of vaccine strategies (Billerbeck et al., 2017). These and other
encouraging advancements have, however, largely been overshadowed by astonishing breakthroughs in clinical HCV treatment. For two decades, interferon-a-based treatments were poorly effective and highly toxic. The past 5 years have witnessed the rapid rollout of various direct-acting antiviral (DAA) combination therapies that can cure HCV-infected patients with minimal side effects. The latest DAA regimens also cure historically challenging patient populations (Vermehren et al., 2018), opening the door to speculation about eradicating HCV. Indeed, modeling studies suggest that widespread testing and DAA treatment can result in HCV eradication from parts of the world, something that just a few years ago would have been unthinkable without a vaccine. An effective HCV vaccine remains highly desirable for several populations, e.g., the rising number of intravenous drug users in the United States, and in areas with poor healthcare infrastructure. Yet after nearly three decades of scientific challenges developing such a vaccine, DAA treatment success may soon become the biggest hurdle. REFERENCES Billerbeck, E., Wolfisberg, R., Fahnøe, U., Xiao, J.W., Quirk, C., Luna, J.M., Cullen, J.M., Hartlage, A.S., Chiriboga, L., Ghoshal, K., et al. (2017). Mouse models of acute and chronic hepacivirus infection. Science 357, 204–208. Bukh, J., Thimme, R., Meunier, J.C., Faulk, K., Spangenberg, H.C., Chang, K.M., Satterfield, W.,
Chisari, F.V., and Purcell, R.H. (2008). Previously infected chimpanzees are not consistently protected against reinfection or persistent infection after reexposure to the identical hepatitis C virus strain. J. Virol. 82, 8183–8195. de Jong, Y.P., Dorner, M., Mommersteeg, M.C., Xiao, J.W., Balazs, A.B., Robbins, J.B., Winer, B.Y., Gerges, S., Vega, K., Labitt, R.N., et al. (2014). Broadly neutralizing antibodies abrogate established hepatitis C virus infection. Sci. Transl. Med. 6, 254ra129. Flyak, A.I., Ruiz, S., Colbert, M., Luong, T., Crowe, J.E., Jr., Bailey, J.R., and Bjorkman, P.J. (2018). Broadly neutralizing antibodies against HCV use a CDRH3 disulfide motif to recognize an E2 glycoprotein site that can be targeted for vaccine design. Cell Host Microbe 24, this issue, 703–716. Houghton, M. (2011). Prospects for prophylactic and therapeutic vaccines against the hepatitis C viruses. Immunol. Rev. 239, 99–108. Kinchen, V.J., Zahid, M.N., Flyak, A.I., Soliman, M.G., Learn, G.H., Wang, S., Davidson, E., Doranz, B.J., Ray, S.C., Cox, A.L., et al. (2018). Broadly neutralizing antibody mediated clearance of human hepatitis C virus infection. Cell Host Microbe 24, this issue, 717–730. Mailly, L., Xiao, F., Lupberger, J., Wilson, G.K., Aubert, P., Duong, F.H.T., Calabrese, D., Leboeuf, C., Fofana, I., Thumann, C., et al. (2015). Clearance of persistent hepatitis C virus infection in humanized mice using a claudin-1-targeting monoclonal antibody. Nat. Biotechnol. 33, 549–554. Park, S.H., and Rehermann, B. (2014). Immune responses to HCV and other hepatitis viruses. Immunity 40, 13–24. Vermehren, J., Park, J.S., Jacobson, I.M., and Zeuzem, S. (2018). Challenges and perspectives of direct antivirals for the treatment of hepatitis C virus infection. J. Hepatol. 69, 1178–1187. Yost, S.A., Wang, Y., and Marcotrigiano, J. (2018). Hepatitis C virus envelope glycoproteins: a balancing act of order and disorder. Front. Immunol. 9, 1917.
Cell Host & Microbe 24, November 14, 2018 621