The dramatically demonstrated the critical need for a deeper understanding of the elements that comprise an effective HIV vaccine. Notably, the ALVAC/AIDSVAX combination used in the RV144 trial elicited a vigorous HIV-specific CD4 T cell response in vaccine recipients. However, the role of virus-specific CD4 T cell responses in the control of HIV replication has not been a subject of intensive HIV vaccine research to date. In fact, vaccine strategies eliciting these responses have been met with skepticism, as HIV-specific CD4 T cells are preferential targets for HIV infection. Nonetheless, despite reports suggesting a preferential infection of HIV-specific CD4+ T cells, the vast majority of HIV-specific CD4 T cells remain uninfected at any time.
In our manuscript published in Science Translational Medicine, we describe a longitudinal study of a very unique patient cohort. These individuals were highly homogenous in terms of gender, race, genetic background and clinical history, and were identified during the earliest days of HIV infection, with exceedingly high viral loads averaging over 3 million copies/ml. All subjects remained treatment-naïve, allowing us to follow their immunological responses over the course of one year post infection. Interestingly, of these individuals, one group was able to control viral replication to a set point of 10,000 copies/ml after one year of infection, while remainder reached a significantly higher viral set point of over 100,000 copies/ml. Although previous reports have suggested a temporal association of early viral control with the emergence of HIV-specific CD8 T cell responses, we nonetheless found no differences in the HIV-specific CD8+ T cell responses between both groups. Likewise, the two subsets were not enriched for protective or deleterious HLA class I alleles. Rather, our data demonstrate that in individuals who progress to a low viral set point, there is a significant early expansion – before changes in the viral set point occur – of HIV-specific CD4 T cell responses with cytolytic activity that is absent from individuals who progress to a high viral set point. Our findings therefore suggest that in this cohort, differences between the two patient groups were driven by a CD4 mediated effect. Indeed, additional experiments revealed that the HIV-specific CD4 T cell responses showed activity associated with cell-killing and could even destroy HIV-infected macrophages – an unusual function for CD4 T cells, which have traditionally been seen as helper cells.
Our data further point to a special role for granzyme A expressed by HIV-specific CD4 T cells. We observed a significantly higher proportion of granzyme A expressing HIV-specific CD4 responses at baseline in individuals who progress to low viral set point compared to those who progress to a high set point. These differences were present at the earliest time point, when viral loads did not differ between both groups, suggesting the presence of this particular HIV-specific response was predictive of disease outcome. Because of the novel nature of this finding, we studied an expanded group of 26 acutely HIV infected individuals without prior knowledge of their clinical status. Stratifying immune responses at baseline, our Kaplan-Meier analysis indeed confirmed that the level of granzyme A in the baseline HIV-specific CD4 T cell response is critically associated with clinical outcome up to three years after initial presentation. Individuals with granzyme Ahigh responses progress significantly slower to the threshold CD4 count of 350 cells/µl and remain off antiretroviral therapy significantly longer than subjects with granzyme Alow responses (p=0.001, and p=0.004). Therefore, our data show that the granzyme A status of the HIV-specific CD4 T cell response at baseline is highly predictive of ultimate disease outcome.
Read study at Science Translational Medicine: Soghoian et al 2012
Read press release of MGH
more details coming soon!
CD4 T cell responses are fundamental in orchestrating the immune response to a pathogen. Yet, few studies have analyzed the contribution of HIV-specific CD4 T cells to the control of HIV, since these cells are particularly susceptible to HIV infection. We therefore conducted a comprehensive study to identify HIV-specific CD4 T cell responses and determine whether these responses are associated with viral control. We measured the magnitude and frequency of HIV-specific CD4 T cell responses in a large group of 93 individuals at different stages of HIV-infection. We observed that HIV-specific responses were detectable in the vast majority of these HIV-infected individuals (92%). Strikingly, we observed that targeting multiple peptides across the HIV proteome was significantly associated with a low viral load and good clinical outcome. In particular, targeting a large number of peptides within Gag protein was highly associated with HIV control. Importantly, the profile of HIV proteins and individual peptides targeted by HIV-specific CD4 T cells were substantially different between individuals defined as ‘HIV controllers’ (that spontaneously controlled HIV replication in the absence of antiretroviral therapy) and ‘HIV progressors’. While HIV controllers dominantly targeted epitopes within Gag at high frequency, HIV progressors predominantly targeted epitopes within Env protein. The ratio of Gag/Env responses is thus a strong marker for viral control. At the level of individual peptides, our study identified three distinct Gag peptides that were linked to spontaneous HIV control and one Env peptide associated with high viral load. Collectively, our study suggests that HIV specific CD4 T cells are likely to make an important contribution to the durable control of HIV at the population level. The identification of proteins and peptides associated with HIV control is highly relevant for HIV vaccine design since their inclusion in a vaccine may help to enhance protective T cell responses.
Reviewed and recommended in: Faculty of a 1000 Medicine by Martin Cranage.
Full article: http://jvi.asm.org/cgi/content/abstract/JVI.05577-11v1
The Streeck lab was well-represented at the 2011 AIDS Vaccine Conference in Bangkok, Thailand. Hendrik, Madelene, and Damien presented oral abstracts, and Srin presented a poster. See below the presented abstracts:
Induction of Neutralizing Antibody Responses in HIV Infection Is Associated with HIV-Specific CD4 T Cell Responses
Background: One of the foremost challenges in the development of an HIV-1 vaccine is that HIV-1 targets CD4-T cells, which are critically important in shaping the immune response to infection. It has been demonstrated that T follicular helper (TFH) CD4-T cells are pivotal for the induction of broadly neutralizing antibody (nAb) responses and for the generation of long-lived B-cell memory maturation. By cognate interaction and cytokine secretion, CD4-T cells expressing CD40L can induce class switching and somatic hypermutation in antigen specific B-cells, which is reflected in the expression of activation induced cytidine deaminase (AID). Nonetheless, the role of TFH cells and their interaction with B-cells in HIV infection is currently unknown. Methods: Ten subjects were identified during acute HIV infection and followed longitudinally over a median of three years. Neutralizing activity of plasma antibodies against a panel of present and past autologous and heterologous viruseswas assessed using a single-replication cycle assay in which full-length envelope genes were incorporated into expression vectors (Monogram Biosciences). Phenotypic and functional characteristics of HIV-specific CD4-T cell responses and their impact on AID expression were assessed longitudinally by multiparameter flow cytometry. Results: The breadth of the broadly neutralizing antibody response to heterologous HIV significantly increased over time in each patient. Interestingly, the expansion in heterologous breadth was not only significantly correlated with an increase in AID expression in B-cells, but also with CD4-T cell expression of PD-1, a marker that has been associated with TFH cells. Moreover, a positive association between AID expression and gp120-specific CD40L-responses was detected at the earliest time point. Conclusion: Our data strongly indicate that the induction of broadly neutralizing antibody responses is linked to the function and activation of HIV-specific CD4-T cell responses. These findings will be pivotal in efforts to generate neutralizing antibody responses by vaccination strategies.
Damien Z. Soghoian
Background: During acute HIV-1 infection, early control of viremia and establishment of viral set point have been widely attributed to HIV-specific CD8 T-cell responses. However, despite increasing evidence for direct antiviral activity by CD4 T-cells in other infections, the impact of HIV-specific CD4 T-cells on viral control has not been studied. Methods: We studied 26 acutely infected, treatment-naı¨ve subjects and monitored their clinical outcome for up to 3 years postinfection. Baseline HIV-specific CD4 T-cell responses were assessed for degranulation (CD107a), IFNc secretion, expression of granzymes (GrzA,B,K) and perforin. HIV-specific cytolytic CD4 T-cell responses were investigated longitudinally in a subset of 11 subjects with similar peak viral loads for 1 year post-infection. Results: Among the patients followed longitudinally, 6 progressed to a low viral set point, while 5 progressed to a significantly higher set point (134,020vs.11,234 copies/ml; p = 0.004). Interestingly, a significant expansion of HIV-specific cytolytic CD4 cell responses was observed in individuals who controlled viral replication compared to those who progressed to a high viral set point (IFNg: p = 0.038, CD107a: p = 0.042). Importantly, this expansion was observed early post-infection, prior to the divergence of viral load or CD4 T cell counts between the two groups. Examination of the baseline HIV-specific CD4 responses revealed a distinct GrzA-enriched cytolytic phenotype that was highly associated with subsequent viral control. Strikingly, Kaplan-Meier analysis of only the baseline cytolytic CD4 T-cell response in a larger cohort demonstrated that individuals with HIV-specific GrzA+ responses remained off HAART significantly longer than individuals with HIV-specific GrzA- responses (p = 0.0023). Conclusion: Here we demonstrate that the rapid induction and expansion of a distinct cytolytic CD4 T-cell response during acute infection is significantly associated with viral control and disease outcome. These data suggest a pivotal role for HIV-specific cytolytic CD4 T-cells in the early control of viremia following acute infection and for future HIV vaccine design strategies.
Spontaneous HIV-1 Control Is Associated with Distinct Epitopes that Promiscuously Bind Multiple HLA Class II Alleles
Background: Although HIV-specific CD4 + T-cells are preferentially infected, there is growing evidence that these cells play a pivotal role in control of viremia. However, little is known about the recognition and HLA-class II restriction of HIV-specific CD4+ T-cells in the setting of chronic or spontaneously controlled HIV-infection. Yet, this knowledge will be crucial for the induction of protective immunity in a prophylactic vaccine. Methods: CD8+ depleted PBMCs from 94 HIV-infected subjects (controller, progressor and ART-treated) were screened for IFNcresponses to 410 overlapping clade B peptides in a modified Elispot. HLA-class II restriction was defined by testing CD4 + Tcell lines against peptide-loaded L-cells transfected with a single HLA-DR. Results: HIV-specific CD4 + T-cell responses were detected in all patient subgroup yet the breadth of these responses was significantly expanded in HIV-controllers (p = 0.029). Most HIVspecific CD4 + T-cells targeted epitopes within Gag, Nef and gp120. Strikingly, we observed significant differences in the immunodominance profile between patient subgroups that distinguished not only elite controllers from rapid progressors, but also from viremic controllers. While elite controllers dominantly targeted a tight cluster of conserved epitopes within p24, chronic progressors preferentially targeted epitopes within the C1/C3 domain of gp120. Moreover, the ratio of Env- and Gag-specific responses was a clear indicator of viral control. A multivariate bootstrap analysis identified four distinct Gag epitopes that were associated with spontaneous control (Probability = 0.60–0.85), while a single gp120 peptide in C3 was associated with high viremia (Probability = 0.82). Detailed characterization showed that promiscuous binding to multiple HLA-DR alleles occurs frequently, and revealed that HLA-DRB1*0701 is associated with slow disease progression (Probability = 0.88). Conclusion: Our data demonstrate that significant differences exist in protein targeting by HIV-specific CD4 + T-cells between controllers and progressors. We also identified distinct epitopes associated with viral control that are conserved and bind promiscuously to multiple HLA-class II alleles, which will be important for vaccine design.
“Role of HIV-specific CD8 T cell responses in the early control of HIV infection”
Background: During acute HIV-1 infection, HIV-specific CD8 T cell (CTL) responses emerge, suppressing viral loads to a semistable viral setpoint; this early viral setpoint has been shown to be highly predictive of disease outcome. However, while immunodominant responses restricted by rare HLA class I alleles have been associated with better control of viral replication, immunodominant responses restricted by common HLA alleles like B*8 or B*7 do not appear to have a significant impact on early control. Methods: Over 600 individuals with primary HIV-1 infection were screened for HLA-restricted, epitope-specific CTL responses using optimally defined epitopes. The early viral setpoint was determined in all treatment-naı¨ve individuals by two independent ID specialists. Results: The recognition of HIV-specific CTL responses was very predictable based on HLA class I expression and followed a clear hierarchical pattern. While the immunodominant responses
in individuals with rare HLA class I alleles were significantly associated with lower viral setpoint, individuals with immunodominant responses restricted by common HLA class I alleles had, on average, higher viral loads. Interestingly, the absence of CTL responses in primary infection directed against some of the immunodominant epitopes restricted by common HLA class I alleles (e.g.HLA-B8-FL8) allowed for the development of responses against subdominant epitopes (e.g.HLAB8- EI8) within the same individuals and was associated with significantly better subsequent viral control(p = 0.001). A distinct ranking of the relative contribution of epitope-specific CTL responses to the early viral setpoint suggested an unexpected contribution of subdominant responses to the initial viral control. Conclusion: Our data suggest that in the context of common HLA class I alleles, CTL responses directed against subdominant epitopes but not dominant epitopes during primary infection significantly contribute to better control of viremia. Thus, engineered proteins that lack common immunodominant CTL epitopes and allow for the priming of otherwise subdominant epitopes might provide an important approach for vaccine design strategies.