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.

HIV has evolved sophisticated mechanisms to avoid restriction by intracellular innate immune defenses that otherwise serve to control acute viral infection and virus dissemination. Innate defenses are triggered when pattern recognition receptor (PRR) proteins of the host cell engage pathogen-associated molecule patterns (PAMPs) present in viral products. Interferon regulatory factor 3 (IRF3) plays a central role in PRR signaling of innate immunity to drive the expression of type I interferon (IFN) and interferon-stimulated genes (ISGs), including a variety of HIV restriction factors, that serve to limit viral replication directly and/or program adaptive immunity. Productive infection of T cells by HIV is dependent upon the targeted proteolysis of IRF3 that occurs through a virus-directed mechanism that results in suppression of innate immune defenses. However, the mechanisms by which HIV controls innate immune signaling and IRF3 function are not defined. Here, we examined the innate immune response induced by HIV strains identified through their differential control of PRR signaling. We identified viruses that, unlike typical circulating HIV strains, lack the ability to degrade IRF3. Our studies show that IRF3 regulation maps specifically to the HIV accessory protein Vpu. We define a molecular interaction between Vpu and IRF3 that redirects IRF3 to the endolysosome for proteolytic degradation, thus allowing HIV to avoid the innate antiviral immune response. Our studies reveal that Vpu is an important IRF3 regulator that supports acute HIV infection through innate immune suppression. These observations define the Vpu-IRF3 interface as a novel target for therapeutic strategies aimed at enhancing the immune response to HIV.

Acute virus infection induces a cell-intrinsic innate immune response comprising our first line of immunity to limit virus replication and spread, but viruses have developed strategies to overcome these defenses. HIV-1 is a major public health problem; however, the virus-host interactions that regulate innate immune defenses against HIV-1 are not fully defined. We have recently identified the viral protein Vpu to be a key determinant responsible for HIV-1 targeting and degradation of interferon regulatory factor 3 (IRF3), a central transcription factor driving host cell innate immunity. IRF3 plays a major role in pathogen recognition receptor (PRR) signaling of innate immunity to drive the expression of type I interferon (IFN) and interferon-stimulated genes (ISGs), including a variety of HIV restriction factors, that serve to limit viral replication directly and/or program adaptive immunity. Here we interrogate the cellular responses to target cell infection with Vpu-deficient HIV-1 strains. Remarkably, in the absence of Vpu, HIV-1 triggers a potent intracellular innate immune response that suppresses infection. Thus, HIV-1 can be recognized by PRRs within the host cell to trigger an innate immune response, and this response is unmasked only in the absence of Vpu. Vpu modulation of IRF3 therefore prevents virus induction of specific innate defense programs that could otherwise limit infection. These observations show that HIV-1 can indeed be recognized as a pathogen in infected cells and provide a novel and effective platform for defining the native innate immune programs of target cells of HIV-1 infection.

Adenovirus (Ad) vectors are widely used as experimental vaccines against several infectious diseases, but the magnitude, phenotype, and functionality of CD8+ T cell responses induced by different adenovirus serotypes have not been compared. To address this question, we have analyzed simian immunodeficiency virus Gag-specific CD8+ T cell responses in mice following vaccination with Ad5, Ad26, and Ad35. Our results show that although Ad5 is more immunogenic than Ad26 and Ad35, the phenotype, function, and recall potential of memory CD8+ T cells elicited by these vectors are substantially different. Ad26 and Ad35 vectors generated CD8+ T cells that display the phenotype and function of long-lived memory T cells, whereas Ad5 vector-elicited CD8+ T cells are of a more terminally differentiated phenotype. In addition, hepatic memory CD8+ T cells elicited by Ad26 and Ad35 mounted more robust recall proliferation following secondary challenge than those induced by Ad5. Furthermore, the boosting potential was higher following priming with alternative-serotype Ad vectors than with Ad5 vectors in heterologous prime-boost regimens. Anamnestic CD8+ T cell responses were further enhanced when the duration between priming and boosting was extended from 30 to 60 days. Our results demonstrate that heterologous prime-boost vaccine regimens with alternative-serotype Ad vectors elicited more functional memory CD8+ T cells than any of the regimens containing Ad5. In summary, these results suggest that alternative-serotype Ad vectors will prove useful as candidates for vaccine development against human immunodeficiency virus type 1 and other pathogens and also emphasize the importance of a longer rest period between prime and boost for generating optimal CD8+ T cell immunity.

Purpose of Review

The recent modest success of the RV144 HIV vaccine trial in Thailand has shown that development of an HIV vaccine is possible. Designing a vaccine that achieves better protection, however, will require a more complete understanding of vaccine mechanisms of action and correlates of protection. Systems biology approaches enable integration of large datasets from a variety of assays and offer new approaches to understanding how vaccine-induced immune responses are coordinately regulated. In this review, we discuss recent advances in clinical trial design, specimen collection, and assay standardization that will generate datasets for systems analyses of immune responses to HIV vaccines.

Recent Findings

Several recently-published HIV vaccine trials have shown that different HIV vaccine prime/boost combinations can greatly affect the immune response generated, but mechanistic insights into their modes of action are lacking. Novel systems biology studies of efficacious, licensed vaccines provide a new template for analysis of HIV vaccines. To generate datasets appropriate for systems analysis, current HIV vaccine clinical trials are undergoing design modifications and increased standardization of specimen collection and immune response assays.

Summary

Systems biology approaches to HIV vaccine evaluation are driving new methods of HIV vaccine immune response profiling in clinical trials, and will hopefully lead to new improved HIV vaccines in the near future.

The HIV Vaccine Trials Network (HVTN) is an international collaboration of scientists and educators facilitating the development of HIV/AIDS preventive vaccines. The HVTN conducts all phases of clinical trials, from evaluating experimental vaccines for safety and immunogenicity, to testing vaccine efficacy. Over the past decade, the HVTN has aimed to improve the process of designing, implementing and analyzing vaccine trials. Several major achievements include streamlining protocol development while maintaining input from diverse stakeholders, establishing a laboratory program with standardized assays and systems allowing for reliable immunogenicity assessments across trials, setting statistical standards for the field and actively engaging with site communities. These achievements have allowed the HVTN to conduct over 50 clinical trials and make numerous scientific contributions to the field.

Background. To investigate the potential immunostimulatory effect of interleukin (IL) 2 as a human immunodeficiency virus type 1 (HIV-1) vaccine adjuvant, we conducted a study of a plasmid coding for a fusion protein of IL-2 and immunoglobulin (IL-2/Ig).

Methods. This phase I trial evaluated an HIV-1 DNA vaccine with the plasmid cytokine adjuvant (IL-2/Ig) in 70 HIV-negative adults. Subjects received placebo (group C), adjuvant alone (group A), vaccine alone (group D), increasing doses of adjuvant concurrent with vaccine (groups T1–T4), or adjuvant given 2 days after vaccine (group T5).

Results. No significant differences in adverse events were observed between treatment groups. Cellular immune responses to envelope protein EnvA peptides were detected by interferon (IFN) γ and IL-2 enzyme-linked immunospot (ELISPOT) assays in 50% and 40% of subjects, respectively, in T4, and in 100% and 80% in T5. The median responses for groups T4 and T5, respectively, were 90 and 193 spot-forming cells (SFCs)/106 peripheral blood mononuclear cells (P = .004; T4 vs T5) for the IL-2 ELISPOT assay and 103 and 380 SFCs/106 PBMCs (P = .003; T4 vs T5) for the IFN-γ ELISPOT assay. A trend to more durable cellular immune responses in T5 was observed at 1 year (T5 vs T4/D; P = .07). Higher anti-Env antibody responses were detected with T5 than with T4.

Conclusions. Plasmid IL-2/Ig significantly increased immune responses when administered 2 days after the DNA vaccine, compared with simultaneous administration. These observations have important implications for the development of cytokine augmentation strategies.

Clinical Trials Registration. NCT00069030.

Most T cell-based HIV-1 vaccine candidates induce responses of limited breadth for reasons that are unclear. We evaluated vaccine-induced T-cell responses in individuals receiving an HIV-1 recombinant adenoviral vaccine. Certain HLA alleles (B27, B57, B35 and B14) are preferentially utilized to mount HIV-specific responses, whereas other alleles (A02 and B07) are rarely utilized (p<0.001). This preference appears due to four factors individually or in combination: higher affinity of specific peptides to specific HLA alleles; higher avidity of TCR; HLA and peptide interaction; and/or higher surface expression of certain HLA. Thus, HLA immunodominance plays a substantial role in vaccine-induced T-cell responses.

BACKGROUND

In the RV144 trial, the estimated efficacy of a vaccine regimen against human immunodeficiency virus type 1 (HIV-1) was 31.2%. We performed a case–control analysis to identify antibody and cellular immune correlates of infection risk.

METHODS

In pilot studies conducted with RV144 blood samples, 17 antibody or cellular assays met prespecified criteria, of which 6 were chosen for primary analysis to determine the roles of T-cell, IgG antibody, and IgA antibody responses in the modulation of infection risk. Assays were performed on samples from 41 vaccinees who became infected and 205 uninfected vaccinees, obtained 2 weeks after final immunization, to evaluate whether immune-response variables predicted HIV-1 infection through 42 months of follow-up.

RESULTS

Of six primary variables, two correlated significantly with infection risk: the binding of IgG antibodies to variable regions 1 and 2 (V1V2) of HIV-1 envelope proteins (Env) correlated inversely with the rate of HIV-1 infection (estimated odds ratio, 0.57 per 1-SD increase; P = 0.02; q = 0.08), and the binding of plasma IgA antibodies to Env correlated directly with the rate of infection (estimated odds ratio, 1.54 per 1-SD increase; P = 0.03; q = 0.08). Neither low levels of V1V2 antibodies nor high levels of Env-specific IgA antibodies were associated with higher rates of infection than were found in the placebo group. Secondary analyses suggested that Env-specific IgA antibodies may mitigate the effects of potentially protective antibodies.

CONCLUSIONS

This immune-correlates study generated the hypotheses that V1V2 antibodies may have contributed to protection against HIV-1 infection, whereas high levels of Env-specific IgA antibodies may have mitigated the effects of protective antibodies. Vaccines that are designed to induce higher levels of V1V2 antibodies and lower levels of Env-specific IgA antibodies than are induced by the RV144 vaccine may have improved efficacy against HIV-1 infection.

Many candidate HIV vaccines are designed to primarily elicit T-cell responses. Although repeated immunization with the same vaccine boosts antibody responses, the benefit for T-cell responses is ill-defined. We compared two immunization regimens that include the same recombinant adenoviral serotype 5 (rAd5) boost. Repeated homologous rAd5 immunization fails to increase T-cell responses, but increases gp140 antibody responses ten-fold. DNA prime, as compared with rAd5 prime, directs long-term memory CD8+ T cells toward a terminally differentiated effector memory phenotype with cytotoxic potential. Based on the kinetics of activated cells measured directly ex vivo, the DNA vaccination primes for both CD4+ and CD8+ T cells, despite the lack of detection of the latter until after the boost. These results suggest that heterologous prime-boost combinations have distinct immunological advantages over homologous prime-boosts, and suggest that the effect of DNA on subsequent boosting may not be easily detectable directly after the DNA vaccination.

Although T lymphocytes are present in the genital mucosa, their function in sexually transmitted diseases is unproven. To determine if cervical T cells mediate HIV-specific cytolysis, mononuclear cells in cytobrush specimens from HIV-1-infected women were stimulated in vitro with antigen. Resultant cell lines lysed autologous targets expressing HIV-1 proteins in 12/19 (63%) subjects, and these responses were detected intermittently on repeated visits. All 8 subjects with blood CD4+ counts ⩾500 cells/μl had HIV-1-specific cervical CTL, whereas only 4/11 with counts <500 cells/μl had detectable responses (P = 0.008). Class II MHC– restricted CD4+ CTL clones lysed targets expressing Env gp41 or infected with HIV-1. Class I MHC-restricted CD8+ clones recognized HIV-1 Gag- or Pol-expressing targets, and the epitopes were mapped to within 9–20 amino acids. Comparisons of intra-individual cervical and blood CTL specificities indicate that epitopes recognized by CTL in the cervix were commonly recognized in the blood. These studies provide the first definitive evidence for an MHC-restricted effector function in human cervical lymphocytes.

Although implied by other models, proof that Langerhans cells (LCs) in the human vagina participate in dissemination of infectious human immunodeficiency virus type 1 (HIV-1) has been lacking. Here, we show that LCs migrate from HIV-1-exposed vaginal epithelia and pass infectious virus to CD4+ T cells without being productively infected themselves, and we point to a pathway that might enable HIV-1 to avoid degradation in vaginal LCs. Transport by migratory LCs to local lymphatics in a nonproductive but infectious form may aid HIV-1 in evasion of topical microbicides that target its intracellular productive life cycle.

Background. A key missing element in the development of a successful human immunodeficiency virus (HIV) vaccine is an immunogen that can generate broadly cross-neutralizing antibodies against primary isolates of the virus.

Methods. This phase 1 clinical trial employed a DNA prime and subunit envelope protein boost in an attempt to generate cellular and humoral immune responses that might be desirable in a protective HIV vaccine. Priming was performed via intramuscular injection with gag and env DNA adsorbed to polylactide coglycolide microspheres, followed by boosting with a recombinant trimeric envelope (Env) glycoprotein delivered in MF59 adjuvant.

Results. The DNA prime and protein boost were generally safe and well-tolerated. Env-specific CD4+ cellular responses were generated that were predominantly detected after Env protein boosting. Neutralizing antibody responses against the homologous SF162 viral isolate were remarkably strong and were present in the majority of vaccine recipients, including a strong response against CD4-induced epitopes on gp120. Despite the promising potency of this vaccine approach, neutralization breadth against heterologous tier 2 strains of HIV-1 was minimal.

Conclusions. Potent neutralization against neutralization-sensitive strains of HIV is achievable in humans through a DNA prime, recombinant oligomeric Env protein boost regimen. Eliciting substantial breadth of neutralization remains an elusive goal.

 Clinical Trials Registration. NCT00073216.

Specific human leukocyte antigens (HLAs), notably HLA-B*27 and HLA-B*57 allele groups, have long been associated with control of HIV-1. Although the majority of HIV-specific CD8+ T cells lose proliferative capacity during chronic infection, T cells restricted by HLA-B*27 or HLAB*57 allele groups do not. Here we show that CD8+ T cells restricted by 'protective' HLA allele groups are not suppressed by Tref cells, whereas, within the same individual, T cells restricted by 'nonprotective' alleles are highly suppressed ex vivo. This differential sensitivity of HIV-specific CD8+ T cells to Tref cell–mediated suppression correlates with their expression of the inhibitory receptor T cell immunoglobulin domain and mucin domain 3 (Tim-3) after stimulation with their cognate epitopes. Furthermore, we show that HLA-B*27– and HLA-B*57–restricted effectors also evade Tref cell–mediated suppression by directly killing Tref cells they encounter in a granzyme B (GzmB)-dependent manner. This study uncovers a previously unknown explanation for why HLA-B*27 and HLA-B*57 allele groups are associated with delayed HIV-1 disease progression.

Understanding how human genetic variation impacts individual response to immunogens is fundamental for rational vaccine development. To explore host mechanisms involved in cellular immune responses to the MRKAd5 human immunodeficiency virus type 1 (HIV-1) gag/pol/nef vaccine tested in the Step trial, we performed a genome-wide association study of determinants of HIV-specific T cell responses, measured by interferon γ enzyme-linked immunospot assays. No human genetic variant reached genome-wide significance, but polymorphisms located in the major histocompatibility complex (MHC) region showed the strongest association with response to the HIV-1 Gag protein: HLA-B alleles known to be associated with differences in HIV-1 control were responsible for these associations. The implication of the same HLA alleles in vaccine-induced cellular immunity and in natural immune control is of relevance for vaccine design. Furthermore, our results demonstrate the importance of considering the host immunogenetic background in the analysis of immune responses to T cell vaccines.

Recombinant viruses hold promise as vectors for vaccines to prevent infectious diseases with significant global health impacts. One of their major limitations is that preexisting anti-vector neutralizing antibodies can reduce T cell responses to the insert antigens; however, the impact of vector-specific cellular immunity on subsequent insert-specific T cell responses has not been assessed in humans. Here, we have identified and compared adenovirus-specific and HIV-specific T cell responses in subjects participating in two HIV-1 vaccine trials using a vaccine vectored by adenovirus serotype 5 (Ad5). Higher frequencies of pre-immunization adenovirus-specific CD4+ T cells were associated with substantially decreased magnitude of HIV-specific CD4+ T cell responses and decreased breadth of HIV-specific CD8+ T cell responses in vaccine recipients, independent of type-specific preexisting Ad5-specific neutralizing antibody titers. Further, epitopes recognized by adenovirus-specific T cells were commonly conserved across many adenovirus serotypes, suggesting that cross-reactivity of preexisting adenovirus-specific T cells can extend to adenovirus vectors derived from rare serotypes. These findings provide what we believe to be a new understanding of how preexisting viral immunity may impact the efficacy of vaccines under current evaluation for prevention of HIV, tuberculosis, and malaria.

SUMMARY

Recent findings have brought optimism that development of a successful human immunodeficiency virus type-1 (HIV-1) vaccine lies within reach. Studies of early events in HIV-1 infection have revealed when and where HIV-1 is potentially vulnerable to vaccine-targeted immune responses. With technical advances in human monoclonal antibody production, clues about how antibodies recognize the HIV-1 envelope proteins have uncovered new antigenic targets for immunogen design. A recent vaccine regimen has shown modest efficacy against HIV-1 acquisition. However, inducing long-term T and B cell memory and coping with HIV-1 diversity remain a high priority. Mediators of innate immunity may play pivotal roles in blocking infection and shaping immunity; vaccine strategies to capture these activities are under intense investigation. Key challenges remain in integrating basic, preclinical and clinical research to improve predictions of types of immunity associated with vaccine efficacy, to apply these insights to immunogen design, and to accelerate evaluation of vaccine efficacy in persons at-risk for acquiring infection.

Unanticipated results from two recent candidate HIV-1 vaccine regimens in large-scale international trials highlight the importance of understanding the optimal earliest immune defense against HIV-1 infection. Presented here are key findings in these vaccine studies that have relevance to the development of future HIV-1 vaccines that can control acute HIV-1 infection.

We evaluated replication-defective poxvirus vectors (modified vaccinia Ankara [MVA] and fowlpox [FPV]) in a homologous and heterologous vector prime-boost vaccination regimen containing matching HIV inserts (MVA-HIV and FPV-HIV) given at months 0, 1, 3, 5 and 7 in 150 healthy HIV-negative vaccinia-naïve participants. FPV-HIV alone was poorly immunogenic, while the high dose (109 pfu/2ml) of MVA-HIV alone elicited maximal responses after two injections: CD4+ and CD8+ T-cell responses in 26/55 (47.3%) and 5/60 (8.3%) of participants, respectively and IFN-γ ELISpot responses in 28/62 (45.2%). The infrequent CD8+ T-cell responses following MVA-HIV priming were boosted only by the heterologous (FPV-HIV) construct in 14/27 [51.9%] of participants post-4th vaccination. Alternatively, HIV envelope-specific binding antibodies were demonstrated in approximately two-thirds of recipients of the homologous boosting regimen, but in less than 20% of subjects after the heterologous vector boost. Thus, a heterologous poxvirus vector prime-boost regimen can induce an HIV-specific CD8+ T-cell and CD4+ T-cell responses, which may be an important feature of an optimal regimen for preventive HIV vaccination.

Improved understanding of the dynamics of host immune responses and viral evolution is critical for effective HIV-1 vaccine design. We comprehensively analyzed Cytotoxic T-lymphocyte (CTL)-viral epitope dynamics in an antiretroviral therapy-naïve subject over the first four years of HIV-1 infection. We found that CTL responses developed sequentially and required constant antigenic stimulation for maintenance. CTL responses exerting strong selective pressure emerged early and led to rapid escape, proliferated rapidly and were predominant during acute/early infection. Although CTL responses to a few persistent epitopes developed over the first two months of infection, they proliferated slowly. As CTL epitopes were replaced by mutational variants, the corresponding responses immediately declined, most rapidly in the cases of strongly selected epitopes. CTL recognition of epitope variants, via cross-reactivity and de novo responses, was common throughout the period of study. Our data demonstrate that HIV-specific CTL responses, especially in the critical acute/early stage, were focused on regions that are prone to escape. Failure of CTL responses to strongly target functional or structurally critical regions of the virus, as well as the sequential cascade of CTL responses, followed closely by viral escape and decline of the corresponding responses, likely contribute to a lack of sustainable viral suppression. Focusing early and rapidly proliferating CTL on persistent epitopes may be essential for durable viral control in HIV-1 infection.

Background

The epitope specificities and antiviral activities of class I HLA-restricted CD8+ T cells, especially those induced during human immunodeficiency virus type 1 (HIV-1) primary infection, are important considerations in designing HIV-1 vaccines. Conserved epitopes may be more commonly and persistently recognized than variable epitopes, as they may be more likely to be present in infecting viruses. However, some studies have shown preferential or similar targeting of variable versus conserved epitopes during primary infection.

Methods

We analyzed cytotoxic T-lymphocyte (CTL) responses toward predefined conserved and variable epitopes in 45 subjects during primary (n = 34) and/or chronic infection (n = 16).

Results

Conserved and variable CTL epitopes were recognized with similar probabilities, whereas conserved epitopes generally elicited subdominant responses during both primary and chronic infection. During primary infection, CTL responses against Gag versus responses against Env and variable epitopes tended to be associated with lower and higher viral loads, respectively. During chronic infection, Env-specific responses tended to be associated with lower CD4+ counts.

Conclusions

Subdominant CTL recognition of conserved HIV-1 epitopes commonly occurs from primary through chronic HIV-1 infection. These findings underscore the challenge in designing T cell based vaccines that can induce immunodominant CTL to conserved HIV-1 regions.

Signatures of natural selection occur throughout the human genome and can be detected at the sequence level. We have re-sequenced ABCE1, a host candidate gene essential for HIV-1 capsid assembly, in European- (n=23) and African-descent (Yoruban; n=24) reference populations for genetic variation discovery. We identified an excess of rare genetic variation in Yoruban samples, and the resulting Tajima’s D was low (−2.27). The trend of excess rare variation persisted in flanking candidate genes ANAPC10 and OTUD4, suggesting that this pattern of positive selection can be detected across the 184.5kb examined on chromosome 4. Because of ABCE1’s role in HIV-1 replication, we re-sequenced the candidate gene in three small cohorts of HIV-1-infected or resistant individuals. We were able to confirm the excess of rare genetic variation among HIV-1 positive African-American individuals (n=53; Tajima’s D = −2.34). These results highlight the potential importance of ABCE1’s role in infectious diseases such as HIV-1.

In the current report, we compared the specificities of antibody responses in sera from volunteers enrolled in three US NIH-supported HIV vaccine trials using different immunization regimens. HIV-1 Env-specific binding antibody, neutralizing antibody, antibody-dependent cell-mediated cytotoxicity (ADCC), and profiles of antibody specificity were analyzed for human immune sera collected from vaccinees enrolled in the NIH HIV Vaccine Trial Network (HVTN) Study #041 (recombinant protein alone), HVTN Study #203 (poxviral vector prime-protein boost), and the DP6-001 study (DNA prime-protein boost). Vaccinees from HVTN Study #041 had the highest neutralizing antibody activities against the sensitive virus along with the highest binding antibody responses, particularly those directed toward the V3 loop. DP6-001 sera showed a higher frequency of positive neutralizing antibody activities against more resistant viral isolate with a significantly higher CD4 binding site (CD4bs) antibody response compared to both HVTN studies #041 and #203. No differences were found in CD4-induced (CD4i) antibody responses, ADCC activity, or complement activation by Env-specific antibody among these sera. Given recent renewed interest in realizing the importance of antibody responses for next generation HIV vaccine development, different antibody profiles shown in the current report, based on the analysis of a wide range of antibody parameters, provide critical biomarker information for the selection of HIV vaccines for more advanced human studies and, in particular, those that can elicit antibodies targeting conformational-sensitive and functionally conserved epitopes.

HLA alleles B57/58, B27, and B35 have the strongest genetic associations with HIV-1 disease progression. The mechanisms of these relationships may be host control of HIV-1 infection via CD8+ T-cell responses. We examined these immune responses in subjects from the Seattle Primary Infection Cohort with these alleles. CD8+ T-cell responses to conserved HIV epitopes within B57/58 alleles (TW10 and KF11) and B27 alleles (KK10 and FY10) delayed declines in CD4+ T-cell counts (4 to 8 times longer), while responses to variable epitopes presented by B35 alleles (DL9 and IL9) resulted in more rapid progression. The plasma viral load was higher in B57/58+ and B27+ subjects lacking the conserved B57/58- and B27-restricted responses. The presence of certain B57/58-, B27-, and B35-restricted HIV-specific CD8+ T-cell responses after primary HIV-1 infection better defined disease progression than the HLA genotype alone, suggesting that it is the HIV-specific CD8+ T cells and not the presence of a particular HLA allele that determine disease progression. Further, the most effective host CD8+ T-cell responses to HIV-1 were prevalent within an HLA allele, represented a high total allele fraction of the host CD8+ T-cell response, and targeted conserved regions of HIV-1. These data suggest that vaccine immunogens should contain only conserved regions of HIV-1.