Targeting of conserved gag-epitopes in early HIV infection is associated with lower plasma viral load and slower CD4(+) T cell depletion.

We aimed to investigate whether the character of the immunodominant HIV-Gag peptide (variable or conserved) targeted by CD8(+) T cells in early HIV infection would influence the quality and quantity of T cell responses, and whether this would affect the rate of disease progression. Treatment-naive HIV-infected study subjects within the OPTIONS cohort at the University of California, San Francisco, were monitored from an estimated 44 days postinfection for up to 6 years. CD8(+) T cells responses targeting HLA-matched HIV-Gag-epitopes were identified and characterized by multicolor flow cytometry. The autologous HIV gag sequences were obtained. We demonstrate that patients targeting a conserved HIV-Gag-epitope in early infection maintained their epitope-specific CD8(+) T cell response throughout the study period. Patients targeting a variable epitope showed decreased immune responses over time, although there was no limitation of the functional profile, and they were likely to target additional variable epitopes. Maintained immune responses to conserved epitopes were associated with no or limited sequence evolution within the targeted epitope. Patients with immune responses targeting conserved epitopes had a significantly lower median viral load over time compared to patients with responses targeting a variable epitope (0.63 log(10) difference). Furthermore, the rate of CD4(+) T cell decline was slower for subjects targeting a conserved epitope (0.85% per month) compared to subjects targeting a variable epitope (1.85% per month). Previous studies have shown that targeting of antigens based on specific HLA types is associated with a better disease course. In this study we show that categorizing epitopes based on their variability is associated with clinical outcome.

Induction of systemic HIV-1-specific cellular immune responses by oral exposure in the uninfected partner of discordant couples.

OBJECTIVES: Previous studies have identified HIV-specific T-cell responses in HIV-exposed uninfected individuals (EUI). However, so far no study has investigated exposure through oral sex. Our aim was to investigate whether oral exposure is enough to induce a systemic HIV-specific T-cell response. DESIGN: Peripheral blood mononuclear cells were collected from 25 EUI living with a HIV-positive partner. Sexual behavior was described by the EUI in self-reported questionnaires. All clinical data of the infected partners were well documented. METHODS: Peripheral blood mononuclear cells were stimulated with five different HIV peptide pools and HIV-specific T-cell responses were detected using the interferon-[gamma] enzyme-linked immunospot assay. Multiple cytokine production was studied longitudinally using flow cytometry intracellular cytokine assay. RESULTS: The majority of the discordant couples reported having protected anal intercourse but unprotected oral sex. Three of the 23 tested EUI with evaluable results had HIV-Gag or Nef-specific T-cell responses. Two of the responders reported unprotected oral sex as the only route of exposure. The HIV-specific CD4+ and CD8+ T cells in the Gag-responder showed production of multiple cytokines. The magnitude of the responses decreased over time when the level of exposure, determined by the viral load in the partner, declined. CONCLUSION: HIV exposure through oral sex is sufficient to induce systemic HIV-specific CD4+ and CD8+ T-cell immune responses in some uninfected individuals. Further investigation is needed to determine whether these responses have any protective role against HIV infection, or are merely evidence of exposure.

Interdisciplinary analysis of HIV-specific CD8+ T cell responses against variant epitopes reveals restricted TCR promiscuity.

HIV-1-specific CTL responses play a key role in limiting viral replication. CTL responses are sensitive to viral escape mutations, which influence recognition of the virus. Although CTLs have been shown to recognize epitope variants, the extent of this cross-reactivity has not been quantitatively investigated in a genetically diverse cohort of HIV-1-infected patients. Using a novel bioinformatic binding prediction method, we aimed to explain the pattern of epitope-specific CTL responses based on the patients' HLA genotype and autologous virus sequence quantitatively. Sequences covering predicted and tested HLA class I-restricted epitopes (peptides) within the HIV-Gag, Pol, and Nef regions were obtained from 26 study subjects resulting in 1492 patient-specific peptide pairs. Epitopes that were recognized in ELISPOT assays were found to be significantly more similar to the autologous virus than those that did not elicit a response. A single substitution in the presented epitope decreased the chance of a CTL response by 40%. The impact of sequence similarity on cross-recognition was confirmed by testing immune responses against multiple variants of six selected epitopes. Substitutions at central positions in the epitope were particularly likely to result in abrogation of recognition. In summary, the presented data demonstrate a highly restricted promiscuity of HIV-1-specific CTL in the recognition of variant epitopes. In addition, our results illustrate that bioinformatic prediction methods are useful to study the complex pattern of CTL responses exhibited by an HIV-1-infected patient cohort and for identification of optimal targets for novel therapeutic or vaccine approaches.

Broadly immunogenic HLA class I supertype-restricted elite CTL epitopes recognized in a diverse population infected with different HIV-1 subtypes.

The genetic variations of the HIV-1 virus and its human host constitute major obstacles for obtaining potent HIV-1-specific CTL responses in individuals of diverse ethnic backgrounds infected with different HIV-1 variants. In this study, we developed and used a novel algorithm to select 184 predicted epitopes representing seven different HLA class I supertypes that together constitute a broad coverage of the different HIV-1 strains as well as the human HLA alleles. Of the tested 184 HLA class I-restricted epitopes, 114 were recognized by at least one study subject, and 45 were novel epitopes, not previously described in the HIV-1 immunology database. In addition, we identified 21 "elite" epitopes that induced CTL responses in at least 4 of the 31 patients. A majority (27 of 31) of the study population recognized one or more of these highly immunogenic epitopes. We also found a limited set of 9 epitopes that together induced HIV-1-specific CTL responses in all HIV-1-responsive patients in this study. Our results have important implications for the validation of potent CTL responses and show that the goal for a vaccine candidate in inducing broadly reactive CTL immune responses is attainable.