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1.  The Major Genetic Determinants of HIV-1 Control Affect HLA Class I Peptide Presentation 
Pereyra, Florencia | Jia, Xiaoming | McLaren, Paul J. | Telenti, Amalio | de Bakker, Paul I.W. | Walker, Bruce D. | Jia, Xiaoming | McLaren, Paul J. | Ripke, Stephan | Brumme, Chanson J. | Pulit, Sara L. | Telenti, Amalio | Carrington, Mary | Kadie, Carl M. | Carlson, Jonathan M. | Heckerman, David | de Bakker, Paul I.W. | Pereyra, Florencia | de Bakker, Paul I.W. | Graham, Robert R. | Plenge, Robert M. | Deeks, Steven G. | Walker, Bruce D. | Gianniny, Lauren | Crawford, Gabriel | Sullivan, Jordan | Gonzalez, Elena | Davies, Leela | Camargo, Amy | Moore, Jamie M. | Beattie, Nicole | Gupta, Supriya | Crenshaw, Andrew | Burtt, Noël P. | Guiducci, Candace | Gupta, Namrata | Carrington, Mary | Gao, Xiaojiang | Qi, Ying | Yuki, Yuko | Pereyra, Florencia | Piechocka-Trocha, Alicja | Cutrell, Emily | Rosenberg, Rachel | Moss, Kristin L. | Lemay, Paul | O’Leary, Jessica | Schaefer, Todd | Verma, Pranshu | Toth, Ildiko | Block, Brian | Baker, Brett | Rothchild, Alissa | Lian, Jeffrey | Proudfoot, Jacqueline | Alvino, Donna Marie L. | Vine, Seanna | Addo, Marylyn M. | Allen, Todd M. | Altfeld, Marcus | Henn, Matthew R. | Le Gall, Sylvie | Streeck, Hendrik | Walker, Bruce D. | Haas, David W. | Kuritzkes, Daniel R. | Robbins, Gregory K. | Shafer, Robert W. | Gulick, Roy M. | Shikuma, Cecilia M. | Haubrich, Richard | Riddler, Sharon | Sax, Paul E. | Daar, Eric S. | Ribaudo, Heather J. | Agan, Brian | Agarwal, Shanu | Ahern, Richard L. | Allen, Brady L. | Altidor, Sherly | Altschuler, Eric L. | Ambardar, Sujata | Anastos, Kathryn | Anderson, Ben | Anderson, Val | Andrady, Ushan | Antoniskis, Diana | Bangsberg, David | Barbaro, Daniel | Barrie, William | Bartczak, J. | Barton, Simon | Basden, Patricia | Basgoz, Nesli | Bazner, Suzane | Bellos, Nicholaos C. | Benson, Anne M. | Berger, Judith | Bernard, Nicole F. | Bernard, Annette M. | Birch, Christopher | Bodner, Stanley J. | Bolan, Robert K. | Boudreaux, Emilie T. | Bradley, Meg | Braun, James F. | Brndjar, Jon E. | Brown, Stephen J. | Brown, Katherine | Brown, Sheldon T. | Burack, Jedidiah | Bush, Larry M. | Cafaro, Virginia | Campbell, Omobolaji | Campbell, John | Carlson, Robert H. | Carmichael, J. Kevin | Casey, Kathleen K. | Cavacuiti, Chris | Celestin, Gregory | Chambers, Steven T. | Chez, Nancy | Chirch, Lisa M. | Cimoch, Paul J. | Cohen, Daniel | Cohn, Lillian E. | Conway, Brian | Cooper, David A. | Cornelson, Brian | Cox, David T. | Cristofano, Michael V. | Cuchural, George | Czartoski, Julie L. | Dahman, Joseph M. | Daly, Jennifer S. | Davis, Benjamin T. | Davis, Kristine | Davod, Sheila M. | Deeks, Steven G. | DeJesus, Edwin | Dietz, Craig A. | Dunham, Eleanor | Dunn, Michael E. | Ellerin, Todd B. | Eron, Joseph J. | Fangman, John J.W. | Farel, Claire E. | Ferlazzo, Helen | Fidler, Sarah | Fleenor-Ford, Anita | Frankel, Renee | Freedberg, Kenneth A. | French, Neel K. | Fuchs, Jonathan D. | Fuller, Jon D. | Gaberman, Jonna | Gallant, Joel E. | Gandhi, Rajesh T. | Garcia, Efrain | Garmon, Donald | Gathe, Joseph C. | Gaultier, Cyril R. | Gebre, Wondwoosen | Gilman, Frank D. | Gilson, Ian | Goepfert, Paul A. | Gottlieb, Michael S. | Goulston, Claudia | Groger, Richard K. | Gurley, T. Douglas | Haber, Stuart | Hardwicke, Robin | Hardy, W. David | Harrigan, P. Richard | Hawkins, Trevor N. | Heath, Sonya | Hecht, Frederick M. | Henry, W. Keith | Hladek, Melissa | Hoffman, Robert P. | Horton, James M. | Hsu, Ricky K. | Huhn, Gregory D. | Hunt, Peter | Hupert, Mark J. | Illeman, Mark L. | Jaeger, Hans | Jellinger, Robert M. | John, Mina | Johnson, Jennifer A. | Johnson, Kristin L. | Johnson, Heather | Johnson, Kay | Joly, Jennifer | Jordan, Wilbert C. | Kauffman, Carol A. | Khanlou, Homayoon | Killian, Robert K. | Kim, Arthur Y. | Kim, David D. | Kinder, Clifford A. | Kirchner, Jeffrey T. | Kogelman, Laura | Kojic, Erna Milunka | Korthuis, P. Todd | Kurisu, Wayne | Kwon, Douglas S. | LaMar, Melissa | Lampiris, Harry | Lanzafame, Massimiliano | Lederman, Michael M. | Lee, David M. | Lee, Jean M.L. | Lee, Marah J. | Lee, Edward T.Y. | Lemoine, Janice | Levy, Jay A. | Llibre, Josep M. | Liguori, Michael A. | Little, Susan J. | Liu, Anne Y. | Lopez, Alvaro J. | Loutfy, Mono R. | Loy, Dawn | Mohammed, Debbie Y. | Man, Alan | Mansour, Michael K. | Marconi, Vincent C. | Markowitz, Martin | Marques, Rui | Martin, Jeffrey N. | Martin, Harold L. | Mayer, Kenneth Hugh | McElrath, M. Juliana | McGhee, Theresa A. | McGovern, Barbara H. | McGowan, Katherine | McIntyre, Dawn | Mcleod, Gavin X. | Menezes, Prema | Mesa, Greg | Metroka, Craig E. | Meyer-Olson, Dirk | Miller, Andy O. | Montgomery, Kate | Mounzer, Karam C. | Nagami, Ellen H. | Nagin, Iris | Nahass, Ronald G. | Nelson, Margret O. | Nielsen, Craig | Norene, David L. | O’Connor, David H. | Ojikutu, Bisola O. | Okulicz, Jason | Oladehin, Olakunle O. | Oldfield, Edward C. | Olender, Susan A. | Ostrowski, Mario | Owen, William F. | Pae, Eunice | Parsonnet, Jeffrey | Pavlatos, Andrew M. | Perlmutter, Aaron M. | Pierce, Michael N. | Pincus, Jonathan M. | Pisani, Leandro | Price, Lawrence Jay | Proia, Laurie | Prokesch, Richard C. | Pujet, Heather Calderon | Ramgopal, Moti | Rathod, Almas | Rausch, Michael | Ravishankar, J. | Rhame, Frank S. | Richards, Constance Shamuyarira | Richman, Douglas D. | Robbins, Gregory K. | Rodes, Berta | Rodriguez, Milagros | Rose, Richard C. | Rosenberg, Eric S. | Rosenthal, Daniel | Ross, Polly E. | Rubin, David S. | Rumbaugh, Elease | Saenz, Luis | Salvaggio, Michelle R. | Sanchez, William C. | Sanjana, Veeraf M. | Santiago, Steven | Schmidt, Wolfgang | Schuitemaker, Hanneke | Sestak, Philip M. | Shalit, Peter | Shay, William | Shirvani, Vivian N. | Silebi, Vanessa I. | Sizemore, James M. | Skolnik, Paul R. | Sokol-Anderson, Marcia | Sosman, James M. | Stabile, Paul | Stapleton, Jack T. | Starrett, Sheree | Stein, Francine | Stellbrink, Hans-Jurgen | Sterman, F. Lisa | Stone, Valerie E. | Stone, David R. | Tambussi, Giuseppe | Taplitz, Randy A. | Tedaldi, Ellen M. | Telenti, Amalio | Theisen, William | Torres, Richard | Tosiello, Lorraine | Tremblay, Cecile | Tribble, Marc A. | Trinh, Phuong D. | Tsao, Alice | Ueda, Peggy | Vaccaro, Anthony | Valadas, Emilia | Vanig, Thanes J. | Vecino, Isabel | Vega, Vilma M. | Veikley, Wenoah | Wade, Barbara H. | Walworth, Charles | Wanidworanun, Chingchai | Ward, Douglas J. | Warner, Daniel A. | Weber, Robert D. | Webster, Duncan | Weis, Steve | Wheeler, David A. | White, David J. | Wilkins, Ed | Winston, Alan | Wlodaver, Clifford G. | Wout, Angelique van’t | Wright, David P. | Yang, Otto O. | Yurdin, David L. | Zabukovic, Brandon W. | Zachary, Kimon C. | Zeeman, Beth | Zhao, Meng
Science (New York, N.Y.)  2010;330(6010):1551-1557.
Infectious and inflammatory diseases have repeatedly shown strong genetic associations within the major histocompatibility complex (MHC); however, the basis for these associations remains elusive. To define host genetic effects on the outcome of a chronic viral infection, we performed genome-wide association analysis in a multiethnic cohort of HIV-1 controllers and progressors, and we analyzed the effects of individual amino acids within the classical human leukocyte antigen (HLA) proteins. We identified >300 genome-wide significant single-nucleotide polymorphisms (SNPs) within the MHC and none elsewhere. Specific amino acids in the HLA-B peptide binding groove, as well as an independent HLA-C effect, explain the SNP associations and reconcile both protective and risk HLA alleles. These results implicate the nature of the HLA–viral peptide interaction as the major factor modulating durable control of HIV infection.
doi:10.1126/science.1195271
PMCID: PMC3235490  PMID: 21051598
3.  HIV Control Is Mediated in Part by CD8+ T-Cell Targeting of Specific Epitopes 
Journal of Virology  2014;88(22):12937-12948.
ABSTRACT
We investigated the hypothesis that the correlation between the class I HLA types of an individual and whether that individual spontaneously controls HIV-1 is mediated by the targeting of specific epitopes by CD8+ T cells. By measuring gamma interferon enzyme-linked immunosorbent spot (ELISPOT) assay responses to a panel of 257 optimally defined epitopes in 341 untreated HIV-infected persons, including persons who spontaneously control viremia, we found that the correlation between HLA types and control is mediated by the targeting of specific epitopes. Moreover, we performed a graphical model-based analysis that suggested that the targeting of specific epitopes is a cause of such control—that is, some epitopes are protective rather than merely associated with control—and identified eight epitopes that are significantly protective. In addition, we use an in silico analysis to identify protein regions where mutations are likely to affect the stability of a protein, and we found that the protective epitopes identified by the ELISPOT analysis correspond almost perfectly to such regions. This in silico analysis thus suggests a possible mechanism for control and could be used to identify protective epitopes that are not often targeted in natural infection but that may be potentially useful in a vaccine. Our analyses thus argue for the inclusion (and exclusion) of specific epitopes in an HIV vaccine.
IMPORTANCE Some individuals naturally control HIV replication in the absence of antiretroviral therapy, and this ability to control is strongly correlated with the HLA class I alleles that they express. Here, in a large-scale experimental study, we provide evidence that this correlation is mediated largely by the targeting of specific CD8+ T-cell epitopes, and we identify eight epitopes that are likely to cause control. In addition, we provide an in silico analysis indicating that control occurs because mutations within these epitopes change the stability of the protein structures. This in silico analysis also identified additional epitopes that are not typically targeted in natural infection but may lead to control when included in a vaccine, provided that other epitopes that would otherwise distract the immune system from targeting them are excluded from the vaccine.
doi:10.1128/JVI.01004-14
PMCID: PMC4249072  PMID: 25165115
4.  Impaired Nef Function Is Associated with Early Control of HIV-1 Viremia 
Journal of Virology  2014;88(17):10200-10213.
ABSTRACT
Host and viral factors influence the HIV-1 infection course. Reduced Nef function has been observed in HIV-1 controllers during the chronic phase, but the kinetics and mechanisms of Nef attenuation in such individuals remain unclear. We examined plasma RNA-derived Nef clones from 10 recently infected individuals who subsequently suppressed viremia to less than 2,000 RNA copies/ml within 1 year postinfection (acute controllers) and 50 recently infected individuals who did not control viremia (acute progressors). Nef clones from acute controllers displayed a lesser ability to downregulate CD4 and HLA class I from the cell surface and a reduced ability to enhance virion infectivity compared to those from acute progressors (all P < 0.01). HLA class I downregulation activity correlated inversely with days postinfection (Spearman's R = −0.85, P = 0.004) and positively with baseline plasma viral load (Spearman's R = 0.81, P = 0.007) in acute controllers but not in acute progressors. Nef polymorphisms associated with functional changes over time were identified in follow-up samples from six controllers. For one such individual, mutational analyses indicated that four polymorphisms selected by HLA-A*31 and B*37 acted in combination to reduce Nef steady-state protein levels and HLA class I downregulation activity. Our results demonstrate that relative control of initial HIV-1 viremia is associated with Nef clones that display reduced function, which in turn may influence the course of HIV-1 infection. Transmission of impaired Nef sequences likely contributed in part to this observation; however, accumulation of HLA-associated polymorphisms in Nef that impair function also suggests that CD8+ T-cell pressures play a role in this phenomenon.
IMPORTANCE Rare individuals can spontaneously control HIV-1 viremia in the absence of antiretroviral treatment. Understanding the host and viral factors that contribute to the controller phenotype may identify new strategies to design effective vaccines or therapeutics. The HIV-1 Nef protein enhances viral pathogenesis through multiple mechanisms. We examined the function of plasma HIV-1 RNA-derived Nef clones isolated from 10 recently infected individuals who subsequently controlled HIV viremia compared to the function of those from 50 individuals who failed to control viremia. Our results demonstrate that early Nef clones from HIV controllers displayed lower HLA class I and CD4 downregulation activity, as well as a reduced ability to enhance virion infectivity. The accumulation of HLA-associated polymorphisms in Nef during the first year postinfection was associated with impaired protein function in some controllers. This report highlights the potential for host immune responses to modulate HIV pathogenicity and disease outcome by targeting cytotoxic T lymphocyte (CTL) epitopes in Nef.
doi:10.1128/JVI.01334-14
PMCID: PMC4136354  PMID: 24965469
5.  Sex Differences in Antiretroviral Therapy Initiation in Pediatric HIV Infection 
PLoS ONE  2015;10(7):e0131591.
The incidence and severity of infections in childhood is typically greater in males. The basis for these observed sex differences is not well understood, and potentially may facilitate novel approaches to reducing disease from a range of conditions. We here investigated sex differences in HIV-infected children in relation to antiretroviral therapy (ART) initiation and post-treatment outcome. In a South African cohort of 2,101 HIV-infected children, we observed that absolute CD4+ count and CD4% were significantly higher in ART-naïve female, compared to age-matched male, HIV-infected children. Absolute CD4 count and CD4% were also significantly higher in HIV-uninfected female versus male neonates. We next showed that significantly more male than female children were initiated on ART (47% female); and children not meeting criteria to start ART by >5yrs were more frequently female (59%; p<0.001). Among ART-treated children, immune reconstitution of CD4 T-cells was more rapid and more complete in female children, even after adjustment for pre-ART absolute CD4 count or CD4% (p=0.011, p=0.030, respectively). However, while ART was initiated as a result of meeting CD4 criteria less often in females (45%), ART initiation as a result of clinical disease in children whose CD4 counts were above treatment thresholds occurred more often in females (57%, p<0.001). The main sex difference in morbidity observed in children initiating ART above CD4 thresholds, above that of TB disease, was as a result of wasting and stunting observed in females with above-threshold CD4 counts (p=0.002). These findings suggest the possibility that optimal treatment of HIV-infected children might incorporate differential CD4 treatment thresholds for ART initiation according to sex.
doi:10.1371/journal.pone.0131591
PMCID: PMC4494714  PMID: 26151555
6.  IL-21 induces antiviral microRNA-29 in CD4 T cells to limit HIV-1 infection 
Nature Communications  2015;6:7562.
Initial events after exposure determine HIV-1 disease progression, underscoring a critical need to understand host mechanisms that interfere with initial viral replication. Although associated with chronic HIV-1 control, it is not known whether interleukin-21 (IL-21) contributes to early HIV-1 immunity. Here we take advantage of tractable primary human lymphoid organ aggregate cultures to show that IL-21 directly suppresses HIV-1 replication, and identify microRNA-29 (miR-29) as an antiviral factor induced by IL-21 in CD4 T cells. IL-21 promotes transcription of all miR-29 species through STAT3, whose binding to putative regulatory regions within the MIR29 gene is enriched by IL-21 signalling. Notably, exogenous IL-21 limits early HIV-1 infection in humanized mice, and lower viremia in vivo is associated with higher miR-29 expression. Together, these findings reveal a novel antiviral IL-21-miR-29 axis that promotes CD4 T-cell-intrinsic resistance to HIV-1 infection, and suggest a role for IL-21 in initial HIV-1 control in vivo.
HIV-infected patients who maintain undetectable virus levels possess elevated plasma concentrations of IL-21. Here, Adoro et al. show that IL-21 inhibits early viral infection in humanized mice and suppresses HIV-1 replication in vitro by upregulating a microRNA via the regulatory protein STAT3.
doi:10.1038/ncomms8562
PMCID: PMC4481879  PMID: 26108174
7.  T cell receptor clonotypes modulate the protective effect of HLA class I alleles in HIV-1 infection 
Nature immunology  2012;13(7):691-700.
Human leukocyte antigen (HLA) B*27 and B*57 are associated with protection against HIV-1 disease progression, yet most persons expressing these alleles are unable to control HIV-1. Here we show that HLA-B*27-restricted CD8+ T cells in controllers and progressors differ in their ability to inhibit virus replication through targeting of the immunodominant Gag epitope. This is associated with distinct TCR clonotypes, characterized by superior control of HIV-1 replication in vitro, greater cross-reactivity against epitope variants, and enhanced perforin delivery. Clonotype-specific differences in antiviral efficacy were also observed for an immunodominant HLA-B*57 restricted response in controllers and progressors. Thus, the efficacy of protective alleles is modulated by specific TCR clonotypes selected in natural infection, providing a functional explanation for divergent HIV-1 outcomes.
doi:10.1038/ni.2342
PMCID: PMC3538851  PMID: 22683743
8.  Discordant Impact of HLA on Viral Replicative Capacity and Disease Progression in Pediatric and Adult HIV Infection 
PLoS Pathogens  2015;11(6):e1004954.
HLA class I polymorphism has a major influence on adult HIV disease progression. An important mechanism mediating this effect is the impact on viral replicative capacity (VRC) of the escape mutations selected in response to HLA-restricted CD8+ T-cell responses. Factors that contribute to slow progression in pediatric HIV infection are less well understood. We here investigate the relationship between VRC and disease progression in pediatric infection, and the effect of HLA on VRC and on disease outcome in adult and pediatric infection. Studying a South African cohort of >350 ART-naïve, HIV-infected children and their mothers, we first observed that pediatric disease progression is significantly correlated with VRC. As expected, VRCs in mother-child pairs were strongly correlated (p = 0.004). The impact of the protective HLA alleles, HLA-B*57, HLA-B*58:01 and HLA-B*81:01, resulted in significantly lower VRCs in adults (p<0.0001), but not in children. Similarly, in adults, but not in children, VRCs were significantly higher in subjects expressing the disease-susceptible alleles HLA-B*18:01/45:01/58:02 (p = 0.007). Irrespective of the subject, VRCs were strongly correlated with the number of Gag CD8+ T-cell escape mutants driven by HLA-B*57/58:01/81:01 present in each virus (p = 0.0002). In contrast to the impact of VRC common to progression in adults and children, the HLA effects on disease outcome, that are substantial in adults, are small and statistically insignificant in infected children. These data further highlight the important role that VRC plays both in adult and pediatric progression, and demonstrate that HLA-independent factors, yet to be fully defined, are predominantly responsible for pediatric non-progression.
Author Summary
HLA plays a central role in determining disease outcome in adult HIV infection. A principal mechanism by which this HLA effect is mediated is via viral replicative capacity (VRC), protective HLA alleles such as HLA-B*57 driving the selection of viral escape mutants that reduce VRC. The factors contributing to the diverse disease progression rates observed in infected children, however, remain uncertain. We here address the role of HLA and VRC in pediatric disease progression in a large cohort in Kimberley, South Africa. The findings highlight the consistent and important role of VRC in both adult and pediatric progression. However, the impact of key HLA molecules in shaping disease outcome in adult infection is notably absent in pediatric infection. Further studies of pediatric infection therefore provide the potential to gain critical new insights into HLA-independent mechanisms of HIV disease non-progression that predominate in HIV-infected but healthy, ART-naive children. Understanding these mechanisms remains of direct relevance to the development of future interventions to minimize HIV disease.
doi:10.1371/journal.ppat.1004954
PMCID: PMC4468173  PMID: 26076345
9.  A cell-intrinsic inhibitor of HIV-1 reverse transcription in CD4+ T cells from elite controllers 
Cell host & microbe  2014;15(6):717-728.
Summary
HIV-1 reverse transcription represents the predominant target for pharmacological inhibition of viral replication, but cell-intrinsic mechanisms that can block HIV-1 reverse transcription in a clinically significant way are poorly defined. We find that effective HIV-1 reverse transcription depends on the phosphorylation of viral reverse transcriptase by host cyclin-dependent kinase (CDK) 2 at a highly conserved Threonin residue. CDK2-dependent phosphorylation increased the efficacy and stability of viral reverse transcriptase and enhanced viral fitness. Interestingly, p21, a cell-intrinsic CDK inhibitor that is upregulated in CD4+ T cells from “elite controllers”, potently inhibited CDK2-dependent phosphorylation of HIV-1 reverse transcriptase and significantly reduced the efficacy of viral reverse transcription. These data suggest that p21 can indirectly block HIV-1 reverse transcription by inhibiting host co-factors supporting HIV-1 replication, and identify sites of viral vulnerability that are effectively targeted in persons with natural control of HIV-1 replication.
doi:10.1016/j.chom.2014.05.011
PMCID: PMC4072498  PMID: 24922574
10.  Potent Cell-Intrinsic Immune Responses in Dendritic Cells Facilitate HIV-1-Specific T Cell Immunity in HIV-1 Elite Controllers 
PLoS Pathogens  2015;11(6):e1004930.
The majority of HIV-1 elite controllers (EC) restrict HIV-1 replication through highly functional HIV-1-specific T cell responses, but mechanisms supporting the evolution of effective HIV-1-specific T cell immunity in these patients remain undefined. Cytosolic immune recognition of HIV-1 in conventional dendritic cells (cDC) can facilitate priming and expansion of HIV-1-specific T cells; however, HIV-1 seems to be able to avoid intracellular immune recognition in cDCs in most infected individuals. Here, we show that exposure of cDCs from EC to HIV-1 leads to a rapid and sustained production of type I interferons and upregulation of several interferon-stimulated effector genes. Emergence of these cell-intrinsic immune responses was associated with a reduced induction of SAMHD1 and LEDGF/p75, and an accumulation of viral reverse transcripts, but inhibited by pharmacological blockade of viral reverse transcription or siRNA-mediated silencing of the cytosolic DNA sensor cGAS. Importantly, improved cell-intrinsic immune recognition of HIV-1 in cDCs from elite controllers translated into stronger abilities to stimulate and expand HIV-1-specific CD8 T cell responses. These data suggest an important role of cell-intrinsic type I interferon secretion in dendritic cells for the induction of effective HIV-1-specific CD8 T cells, and may be helpful for eliciting functional T cell immunity against HIV-1 for preventative or therapeutic clinical purposes.
Author Summary
Elite controllers (EC), a small group of HIV-1-infected individuals that are able to control viral replication in the absence of antiretroviral therapy, provide living evidence that the human immune system is able to spontaneously control HIV-1 infection and serve as a model for inducing a functional cure of HIV-1 infection in broader patient populations. Prior studies indicated that T cell-mediated immune responses represent the backbone of effective antiviral immune defense in EC; however, emerging studies suggest that innate and cell-intrinsic immune activities may have critical roles for supporting and enhancing HIV-1-specific T cells. Here, we performed a detailed investigation of conventional dendritic cells (cDC) from elite controllers and their responses to HIV-1 infection. These studies indicate that cDC from EC have improved abilities to sense cytosolic HIV-1 replication products, and can more effectively mount cell-intrinsic type I interferon (IFN) secretion in response to HIV-1 infection. Notably, such increased production of type I IFN in response to viral antigen translated into enhanced abilities to prime and expand HIV-1-specific T cells. Together, these data suggest that a fine-tuned interplay between innate dendritic cell responses and adaptive HIV-1-specific CD8 T cells represents a critical component of antiviral immune defense in elite controllers.
doi:10.1371/journal.ppat.1004930
PMCID: PMC4466270  PMID: 26067651
11.  Is an HIV Vaccine Possible? 
Journal of acquired immune deficiency syndromes (1999)  2012;60(0 2):10.1097/QAI.0b013e31825b7118.
Although many new prevention modalities that include the use of antiretroviral drugs (ARVs) show promise, there is no question that a global solution to the HIV epidemic will not be economically or logistically feasible without the development of vaccine that provides durable protection. In the best case scenario, the vaccine has to protect against acquisition of infection, likely mediated by Env-specific B cell responses combined with CD4+ T cell responses to evoke full maturation and maintenance of protective antibodies. But HIV-specific CD8+ T cell responses are also likely to be a key element, particularly for those inevitable situations in which full vaccine-induced protection from acquisition is not achieved, in which case durable control of established infection will be required. Although there is reason to be optimistic that an effective HIV vaccine is possible, one of the major constraints moving forward will likely be constraints on funding to support a diversity of concepts at a time that the correlates of protection from acquisition and disease progression are still unknown. Given the scope of the epidemic and the economic climate, we must strive to do much more with less and seek to access additional resources, both scientific and monetary, from every possible source.
doi:10.1097/QAI.0b013e31825b7118
PMCID: PMC3401528  PMID: 22772390
Vaccine; Antiretrovirals; Economy
12.  Profiling Human Antibody Responses by Integrated Single-Cell Analysis 
Vaccine  2014;32(24):2866-2873.
Comprehensive characterization of the antigen-specific B cells induced during infections or following vaccination would facilitate the discovery of novel antibodies and inform how interventions shape protective humoral responses. The analysis of human B cells and their antibodies has been performed using flow cytometry to evaluate memory B cells and expanded plasmablasts, while microtechnologies have also provided a useful tool to examine plasmablasts/plasma cells after vaccination. Here we present an integrated analytical platform using arrays of subnanoliter wells (nanowells) for constructing detailed profiles for human B cells comprising the immunophenotypes of the cells, the distribution of isotypes of secreted antibodies, the specificity and relative affinity for defined antigens, and for a subset of cells, the genes encoding the heavy and light chains. The approach combines on-chip image cytometry, microengraving, and single-cell RT-PCR. Using clinical samples from HIV-infected subjects, we demonstrate that the method can identify antigen-specific neutralizing antibodies, is compatible with both plasmablasts/plasma cells and activated memory B cells, and is well-suited for characterizing the limited numbers of B cells isolated from tissue biopsies (e.g., colonic biopsies). The technology should facilitate detailed analyses of human humoral responses for evaluating vaccines and their ability to raise protective antibody responses across multiple anatomical compartments.
doi:10.1016/j.vaccine.2014.02.020
PMCID: PMC4164152  PMID: 24602776
Microengraving; humoral responses; immune profiling; plasma and memory B cells analysis; nanowells
13.  HIV Subtype Influences HLA-B*07:02-Associated HIV Disease Outcome 
Abstract
Genetic polymorphisms within the MHC encoding region have the strongest impact on HIV disease progression of any in the human genome and provide important clues to the mechanisms of HIV immune control. Few analyses have been undertaken of HLA alleles associated with rapid disease progression. HLA-B*07:02 is an HLA class I molecule that is prevalent in most populations worldwide and that has previously been consistently linked to accelerated disease progression in B-clade infection. This study investigates the observation that HLA-B*07:02 is not associated with a high viral setpoint in C-clade infection. We examine the hypothesis that this clade-specific difference in association with disease outcome may be related to distinct targeting of CD8+ T cell epitopes. We observed that C-clade-infected individuals with HLA-B*07:02 target a broader range of Gag epitopes, and to higher magnitudes, than do individuals infected with B-clade infection. In particular, a novel p17-Gag (Gag22-30, RPGGKKHYM) epitope is targeted in >50% of HLA-B*07:02-positive C-clade-infected individuals but clade-specific differences in this epitope result in nonimmunogenicity in B-clade infection. Only the C-clade p24-Gag “GL9” (Gag355-363, GPSHKARVL) epitope-specific CD8+ T cell response out of 16 studied was associated with a low viral setpoint. Although this epitope was also targeted in B-clade infection, the escape mutant S357S is present at higher frequency in B-clade infection than in C-clade infection (70% versus 43% in HLA-B*07:02-negative subjects). These data support earlier studies suggesting that increased breadth of the Gag-specific CD8+ T cell response may contribute to improved HIV immune control irrespective of the particular HLA molecules expressed.
doi:10.1089/aid.2013.0197
PMCID: PMC4010166  PMID: 24010680
14.  Modest Attenuation of HIV-1 Vpu Alleles Derived from Elite Controller Plasma 
PLoS ONE  2015;10(3):e0120434.
In the absence of antiretroviral therapy, infection with human immunodeficiency virus type 1 (HIV-1) can typically not be controlled by the infected host and results in the development of acquired immunodeficiency. In rare cases, however, patients spontaneously control HIV-1 replication. Mechanisms by which such elite controllers (ECs) achieve control of HIV-1 replication include particularly efficient immune responses as well as reduced fitness of the specific virus strains. To address whether polymorphisms in the accessory HIV-1 protein Vpu are associated with EC status we functionally analyzed a panel of plasma-derived vpu alleles from 15 EC and 16 chronic progressor (CP) patients. Antagonism of the HIV particle release restriction by the intrinsic immunity factor CD317/tetherin was well conserved among EC and CP Vpu alleles, underscoring the selective advantage of this Vpu function in HIV-1 infected individuals. In contrast, interference with CD317/tetherin induced NF-κB activation was little conserved in both groups. EC Vpus more frequently displayed reduced ability to downregulate cell surface levels of CD4 and MHC class I (MHC-I) molecules as well as of the NK cell ligand NTB-A. Polymorphisms potentially associated with high affinity interactions of the inhibitory killer immunoglobulin-like receptor (KIR) KIR2DL2 were significantly enriched among EC Vpus but did not account for these functional differences. Together these results suggest that in a subgroup of EC patients, some Vpu functions are modestly reduced, possibly as a result of host selection.
doi:10.1371/journal.pone.0120434
PMCID: PMC4368696  PMID: 25793728
15.  High Frequency of Transmitted HIV-1 Gag HLA Class I-Driven Immune Escape Variants but Minimal Immune Selection over the First Year of Clade C Infection 
PLoS ONE  2015;10(3):e0119886.
In chronic HIV infection, CD8+ T cell responses to Gag are associated with lower viral loads, but longitudinal studies of HLA-restricted CD8+ T cell-driven selection pressure in Gag from the time of acute infection are limited. In this study we examined Gag sequence evolution over the first year of infection in 22 patients identified prior to seroconversion. A total of 310 and 337 full-length Gag sequences from the earliest available samples (median = 14 days after infection [Fiebig stage I/II]) and at one-year post infection respectively were generated. Six of 22 (27%) individuals were infected with multiple variants. There was a trend towards early intra-patient viral sequence diversity correlating with viral load set point (p = 0.07, r = 0.39). At 14 days post infection, 59.7% of Gag CTL epitopes contained non-consensus polymorphisms and over half of these (35.3%) comprised of previously described CTL escape variants. Consensus and variant CTL epitope proportions were equally distributed irrespective of the selecting host HLA allele and most epitopes remained unchanged over 12 months post infection. These data suggest that intrapatient diversity during acute infection is an indicator of disease outcome. In this setting, there is a high rate of transmitted CTL escape variants and limited immune selection in Gag during the first year of infection. These data have relevance for vaccine strategies designed to elicit effective CD8+ T cell immune responses.
doi:10.1371/journal.pone.0119886
PMCID: PMC4363590  PMID: 25781986
16.  Long-Term Antiretroviral Treatment Initiated at Primary HIV-1 Infection Affects the Size, Composition, and Decay Kinetics of the Reservoir of HIV-1-Infected CD4 T Cells 
Journal of Virology  2014;88(17):10056-10065.
ABSTRACT
Initiation of antiretroviral therapy during the earliest stages of HIV-1 infection may limit the seeding of a long-lasting viral reservoir, but long-term effects of early antiretroviral treatment initiation remain unknown. Here, we analyzed immunological and virological characteristics of nine patients who started antiretroviral therapy at primary HIV-1 infection and remained on suppressive treatment for >10 years; patients with similar treatment duration but initiation of suppressive therapy during chronic HIV-1 infection served as controls. We observed that independently of the timing of treatment initiation, HIV-1 DNA in CD4 T cells decayed primarily during the initial 3 to 4 years of treatment. However, in patients who started antiretroviral therapy in early infection, this decay occurred faster and was more pronounced, leading to substantially lower levels of cell-associated HIV-1 DNA after long-term treatment. Despite this smaller size, the viral CD4 T cell reservoir in persons with early treatment initiation consisted more dominantly of the long-lasting central-memory and T memory stem cells. HIV-1-specific T cell responses remained continuously detectable during antiretroviral therapy, independently of the timing of treatment initiation. Together, these data suggest that early HIV-1 treatment initiation, even when continued for >10 years, is unlikely to lead to viral eradication, but the presence of low viral reservoirs and durable HIV-1 T cell responses may make such patients good candidates for future interventional studies aiming at HIV-1 eradication and cure.
IMPORTANCE Antiretroviral therapy can effectively suppress HIV-1 replication to undetectable levels; however, HIV-1 can persist despite treatment, and viral replication rapidly rebounds when treatment is discontinued. This is mainly due to the presence of latently infected CD4 T cells, which are not susceptible to antiretroviral drugs. Starting treatment in the earliest stages of HIV-1 infection can limit the number of these latently infected cells, raising the possibility that these viral reservoirs are naturally eliminated if suppressive antiretroviral treatment is continued for extremely long periods of time. Here, we analyzed nine patients who started on antiretroviral therapy within the earliest weeks of the disease and continued treatment for more than 10 years. Our data show that early treatment accelerated the decay of infected CD4 T cells and led to very low residual levels of detectable HIV-1 after long-term therapy, levels that were otherwise detectable in patients who are able to maintain a spontaneous, drug-free control of HIV-1 replication. Thus, long-term antiretroviral treatment started during early infection cannot eliminate HIV-1, but the reduced reservoirs of HIV-1 infected cells in such patients may increase their chances to respond to clinical interventions aiming at inducing a drug-free remission of HIV-1 infection.
doi:10.1128/JVI.01046-14
PMCID: PMC4136362  PMID: 24965451
17.  Mosaic HIV-1 Gag antigens can be Processed and Presented to human HIV-specific CD8+ T cells 
Polyvalent “mosaic” HIV immunogens offer a potential solution for generating vaccines that can elicit immune responses against genetically diverse viruses. However, it is unclear whether key T cell epitopes can be processed and presented from these synthetic antigens and recognized by epitope-specific human T cells. Here we tested the ability of mosaic HIV immunogens expressed by recombinant, replication-incompetent adenovirus serotype 26 vectors to process and present major HIV clade B and clade C CD8 T cell epitopes in human cells. A bivalent mosaic vaccine expressing HIV Gag sequences was used to transduce PBMC from 12 HIV-1-infected individuals from the US and 10 HIV-1-infected individuals from South Africa, and intracellular cytokine staining together with tetramer staining was used to assess the ability of mosaic Gag antigens to stimulate pre-existing memory responses compared to natural clade B and C vectors. Mosaic Gag antigens expressed all 8 clade B epitopes tested in 12 US subjects and all 5 clade C epitopes tested in 10 South African subjects. Overall, the magnitude of cytokine production induced by stimulation with mosaic antigens was comparable to clade B and clade C antigens tested, but the mosaic antigens elicited greater cross-clade recognition. Additionally, mosaic antigens also induced HIV-specific CD4 T cell responses. Our studies demonstrate that mosaic antigens express major clade B and clade C viral T cell epitopes in human cells, and support the evaluation of mosaic HIV-1 vaccines in humans.
doi:10.4049/jimmunol.1004231
PMCID: PMC3129742  PMID: 21576505
18.  Impaired Replication Capacity of Acute/Early Viruses in Persons Who Become HIV Controllers▿  
Journal of Virology  2010;84(15):7581-7591.
Human immunodeficiency virus type 1 (HIV-1) controllers maintain viremia at <2,000 RNA copies/ml without antiretroviral therapy. Viruses from controllers with chronic infection were shown to exhibit impaired replication capacities, in part associated with escape mutations from cytotoxic-T-lymphocyte (CTL) responses. In contrast, little is known about viruses during acute/early infection in individuals who subsequently become HIV controllers. Here, we examine the viral replication capacities, HLA types, and virus sequences from 18 HIV-1 controllers identified during primary infection. gag-protease chimeric viruses constructed using the earliest postinfection samples displayed significantly lower replication capacities than isolates from persons who failed to control viremia (P = 0.0003). Protective HLA class I alleles were not enriched in these early HIV controllers, but viral sequencing revealed a significantly higher prevalence of drug resistance mutations associated with impaired viral fitness in controllers than in noncontrollers (6/15 [40.0%] versus 10/80 [12.5%], P = 0.018). Moreover, of two HLA-B57-positive (B57+) controllers identified, both harbored, at the earliest time point tested, signature escape mutations within Gag that likewise impair viral replication capacity. Only five controllers did not express “protective” alleles or harbor viruses with drug resistance mutations; intriguingly, two of them displayed typical B57 signature mutations (T242N), suggesting the acquisition of attenuated viruses from B57+ donors. These data indicate that acute/early stage viruses from persons who become controllers have evidence of reduced replication capacity during the initial stages of infection which is likely associated with transmitted or acquired CTL escape mutations or transmitted drug resistance mutations. These data suggest that viral dynamics during acute infection have a major impact on HIV disease outcome.
doi:10.1128/JVI.00286-10
PMCID: PMC2897600  PMID: 20504921
19.  HLA-Associated Viral Mutations Are Common in Human Immunodeficiency Virus Type 1 Elite Controllers▿  
Journal of Virology  2009;83(7):3407-3412.
Elite controllers (EC) of human immunodeficiency virus type 1 (HIV-1) maintain viremia below the limit of detection without antiretroviral treatment. Virus-specific cytotoxic CD8+ T lymphocytes are believed to play a crucial role in viral containment, but the degree of immune imprinting and compensatory mutations in EC is unclear. We obtained plasma gag, pol, and nef sequences from HLA-diverse subjects and found that 30 to 40% of the predefined HLA-associated polymorphic sites show evidence of immune selection pressure in EC, compared to approximately 50% of the sites in chronic progressors. These data indicate ongoing viral replication and escape from cytotoxic T lymphocytes are present even in strictly controlled HIV-1 infection.
doi:10.1128/JVI.02459-08
PMCID: PMC2655568  PMID: 19153230
20.  HLA-B57/B*5801 Human Immunodeficiency Virus Type 1 Elite Controllers Select for Rare Gag Variants Associated with Reduced Viral Replication Capacity and Strong Cytotoxic T-Lymphotye Recognition▿  
Journal of Virology  2008;83(6):2743-2755.
Human immunodeficiency virus type 1 (HIV-1) elite controllers (EC) maintain viremia below the limit of commercial assay detection (<50 RNA copies/ml) in the absence of antiviral therapy, but the mechanisms of control remain unclear. HLA-B57 and the closely related allele B*5801 are particularly associated with enhanced control and recognize the same Gag240-249 TW10 epitope. The typical escape mutation (T242N) within this epitope diminishes viral replication capacity in chronically infected persons; however, little is known about TW10 epitope sequences in residual replicating viruses in B57/B*5801 EC and the extent to which mutations within this epitope may influence steady-state viremia. Here we analyzed TW10 in a total of 50 B57/B*5801-positive subjects (23 EC and 27 viremic subjects). Autologous plasma viral sequences from both EC and viremic subjects frequently harbored the typical cytotoxic T-lymphocyte (CTL)-selected mutation T242N (15/23 sequences [65.2%] versus 23/27 sequences [85.1%], respectively; P = 0.18). However, other unique mutants were identified in HIV controllers, both within and flanking TW10, that were associated with an even greater reduction in viral replication capacity in vitro. In addition, strong CTL responses to many of these unique TW10 variants were detected by gamma interferon-specific enzyme-linked immunospot assay. These data suggest a dual mechanism for durable control of HIV replication, consisting of viral fitness loss resulting from CTL escape mutations together with strong CD8 T-cell immune responses to the arising variant epitopes.
doi:10.1128/JVI.02265-08
PMCID: PMC2648254  PMID: 19116253
21.  Innate partnership of HLA-B and KIR3DL1 subtypes against HIV-1 
Nature genetics  2007;39(6):733-740.
Allotypes of the natural killer (NK) cell receptor KIR3DL1 vary in both NK cell expression patterns and inhibitory capacity upon binding to their ligands, HLA-B Bw4 molecules, present on target cells. Using a sample size of over 1,500 human immunodeficiency virus (HIV)+ individuals, we show that various distinct allelic combinations of the KIR3DL1 and HLA-B loci significantly and strongly influence both AIDS progression and plasma HIV RNA abundance in a consistent manner. These genetic data correlate very well with previously defined functional differences that distinguish KIR3DL1 allotypes. The various epistatic effects observed here for common, distinct KIR3DL1 and HLA-B Bw4 combinations are unprecedented with regard to any pair of genetic loci in human disease, and indicate that NK cells may have a critical role in the natural history of HIV infection.
doi:10.1038/ng2035
PMCID: PMC4135476  PMID: 17496894
22.  Histone Deacetylase Inhibitors Impair the Elimination of HIV-Infected Cells by Cytotoxic T-Lymphocytes 
PLoS Pathogens  2014;10(8):e1004287.
Resting memory CD4+ T-cells harboring latent HIV proviruses represent a critical barrier to viral eradication. Histone deacetylase inhibitors (HDACis), such as suberanilohydroxamic acid (SAHA), romidepsin, and panobinostat have been shown to induce HIV expression in these resting cells. Recently, it has been demonstrated that the low levels of viral gene expression induced by a candidate HDACi may be insufficient to cause the death of infected cells by viral cytopathic effects, necessitating their elimination by immune effectors, such as cytotoxic T-lymphocytes (CTL). Here, we study the impact of three HDACis in clinical development on T-cell effector functions. We report two modes of HDACi-induced functional impairment: i) the rapid suppression of cytokine production from viable T-cells induced by all three HDACis ii) the selective death of activated T-cells occurring at later time-points following transient exposures to romidepsin or, to a lesser extent, panobinostat. As a net result of these factors, HDACis impaired CTL-mediated IFN-γ production, as well as the elimination of HIV-infected or peptide-pulsed target cells, both in liquid culture and in collagen matrices. Romidepsin exerted greater inhibition of antiviral function than SAHA or panobinostat over the dose ranges tested. These data suggest that treatment with HDACis to mobilize the latent reservoir could have unintended negative impacts on the effector functions of CTL. This could influence the effectiveness of HDACi-based eradication strategies, by impairing elimination of infected cells, and is a critical consideration for trials where therapeutic interruptions are being contemplated, given the importance of CTL in containing rebound viremia.
Author Summary
The advent of antiretroviral therapy has greatly improved the prognosis for HIV-infected individuals with access to care. However, current therapies are unable to cure infection, committing treated individuals to a lifetime of medication with significant economic burden. Furthermore, it has become clear that antiretroviral therapy does not completely restore health, leaving treated HIV-infected individuals at increased risk of cardiovascular disease, neurological disorders, and other health issues. Thus, there is a need to develop therapies capable of curing HIV infection. It is thought that, to be successful, curative strategies will need to combine a means to flush the virus out of the latently-infected cells in which it hides, with a means to kill these unmasked targets. A front-running approach proposes to use a class of drugs called histone deacetylase inhibitors (HDACis) as flushing agents, with cytotoxic T-lymphocytes (CTL, or killer T-cells) to purge viral reservoirs. Here, we uncover an unexpected negative interaction between these two agents, whereby HDACis suppress the ability of CTL to kill HIV-infected cells. This interaction has the potential to limit the effectiveness of combining CTL with HDACis in flush and kill approaches to HIV eradication, and should be considered in the prioritization and optimization of potential curative strategies.
doi:10.1371/journal.ppat.1004287
PMCID: PMC4133386  PMID: 25122219
23.  The Fitness Landscape of HIV-1 Gag: Advanced Modeling Approaches and Validation of Model Predictions by In Vitro Testing 
PLoS Computational Biology  2014;10(8):e1003776.
Viral immune evasion by sequence variation is a major hindrance to HIV-1 vaccine design. To address this challenge, our group has developed a computational model, rooted in physics, that aims to predict the fitness landscape of HIV-1 proteins in order to design vaccine immunogens that lead to impaired viral fitness, thus blocking viable escape routes. Here, we advance the computational models to address previous limitations, and directly test model predictions against in vitro fitness measurements of HIV-1 strains containing multiple Gag mutations. We incorporated regularization into the model fitting procedure to address finite sampling. Further, we developed a model that accounts for the specific identity of mutant amino acids (Potts model), generalizing our previous approach (Ising model) that is unable to distinguish between different mutant amino acids. Gag mutation combinations (17 pairs, 1 triple and 25 single mutations within these) predicted to be either harmful to HIV-1 viability or fitness-neutral were introduced into HIV-1 NL4-3 by site-directed mutagenesis and replication capacities of these mutants were assayed in vitro. The predicted and measured fitness of the corresponding mutants for the original Ising model (r = −0.74, p = 3.6×10−6) are strongly correlated, and this was further strengthened in the regularized Ising model (r = −0.83, p = 3.7×10−12). Performance of the Potts model (r = −0.73, p = 9.7×10−9) was similar to that of the Ising model, indicating that the binary approximation is sufficient for capturing fitness effects of common mutants at sites of low amino acid diversity. However, we show that the Potts model is expected to improve predictive power for more variable proteins. Overall, our results support the ability of the computational models to robustly predict the relative fitness of mutant viral strains, and indicate the potential value of this approach for understanding viral immune evasion, and harnessing this knowledge for immunogen design.
Author Summary
At least 70 million people have been infected with HIV since the beginning of the epidemic and an effective vaccine remains elusive. The high mutation rate and diversity of HIV strains enables the virus to effectively evade host immune responses, presenting a significant challenge for HIV vaccine design. We have developed an approach to translate clinical databases of HIV sequences into mathematical models quantifying the capacity of the virus to replicate as a function of mutations within its genome. We have previously shown how such “fitness landscapes” can be used to guide the design of vaccines to attack vulnerable regions from which it is difficult for the virus to escape by mutation. Here, using new modeling approaches, we have improved on our previous models of HIV fitness landscape by accounting for undersampling of HIV sequences and the specific identity of mutant amino acids. We experimentally tested the accuracy of the improved models to predict the fitness of HIV with multiple mutations in the Gag protein. The experimental data are in strong agreement with model predictions, supporting the value of these models as a novel approach for determining mutational vulnerabilities of HIV-1, which, in turn, can inform vaccine design.
doi:10.1371/journal.pcbi.1003776
PMCID: PMC4125067  PMID: 25102049
24.  HIV-1 persistence in CD4+ T cells with stem cell-like properties 
Nature medicine  2014;20(2):139-142.
Cellular HIV-1 reservoirs that persist despite antiretroviral treatment are incompletely defined. We show that during suppressive antiretroviral therapy, CD4+ T memory stem cells (TSCM) harbor high per-cell levels of HIV-1 DNA, and make increasing contributions to the total viral CD4+ T cell reservoir over time. Moreover, phylogenetic studies suggested long-term persistence of viral quasispecies in CD4+ TSCM cells. Thus, HIV-1 may exploit stem cell characteristics of cellular immune memory to promote long-term viral persistence.
doi:10.1038/nm.3445
PMCID: PMC3959167  PMID: 24412925
25.  Lack of Association between HLA Class II Alleles and In Vitro Replication Capacities of Recombinant Viruses Encoding HIV-1 Subtype C Gag-Protease from Chronically Infected Individuals 
Journal of Virology  2012;86(2):1273-1276.
It is unknown whether favorable HLA class II alleles may attenuate HIV-1 through selection pressure in a manner similar to that of protective HLA class I alleles. We investigated the relationship between HLA class II alleles and in vitro replication capacities of recombinant viruses encoding HIV-1 subtype C Gag-protease from chronically infected individuals. No associations were found between individual alleles and lower replication capacity, suggesting no significant HIV-1 attenuation by HLA class II-restricted Gag-specific CD4+ T cell immune pressure.
doi:10.1128/JVI.06533-11
PMCID: PMC3255856  PMID: 22090116

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