Adaptation of CD8 T cell responses to changing HIV-1 sequences in a cohort of HIV-1 infected individuals not selected for a certain HLA allele.

HIV evades CD8 T cell mediated pressure by viral escape mutations in targeted CD8 T cell epitopes. A viral escape mutation can lead to a decline of the respective CD8 T cell response. Our question was what happened after the decline of a CD8 T cell response and - in the case of viral escape - if a new CD8 T cell response towards the mutated antigen could be generated in a population not selected for certain HLA alleles. We studied 19 antiretroviral-naïve HIV-1 infected individuals with different disease courses longitudinally. A median number of 12 (range 2-24) CD8 T cell responses towards Gag and Nef were detected per study subject. A total of 30 declining CD8 T cell responses were studied in detail and viral sequence analyses showed amino acid changes in 25 (83%) of these. Peptide titration assays and definition of optimal CD8 T cell epitopes revealed 12 viral escape mutations with one de-novo response (8%). The de-novo response, however, showed less effector functions than the original CD8 T cell response. In addition we identified 4 shifts in immunodominance. For one further shift in immunodominance, the mutations occurred outside the optimal epitope and might represent processing changes. Interestingly, four adaptations to the virus (the de-novo response and 3 shifts in immunodominance) occurred in the group of chronically infected progressors. None of the subjects with adaptation to the changing virus carried the HLA alleles B57, B*58:01 or B27. Our results show that CD8 T cell responses adapt to the mutations of HIV. However it was limited to only 20% (5 out of 25) of the epitopes with viral sequence changes in a cohort not expressing protective HLA alleles.

Control of M184V HIV-1 mutants by CD8 T-cell responses.

Antiretroviral treatment directed against HIV is highly effective, yet limited by drug resistance mutations. We hypothesized that CD8 T cells targeting drug-resistant HIV mutants are able to inhibit viral replication in the setting of a failing therapeutic regimen. We evaluated CD8 T-cell responses and mapped epitopes in HIV-infected patients by interferon-gamma Elispot and intracellular cytokine staining. Autologous virus was sequenced by RT-PCR. Viral replication inhibition assays were performed using M184V mutant virus and CD8 T cell lines. CD8 T-cell responses toward the regions of viral drug resistance mutations in Pol are frequent. Focusing on the M184V mutation, A*02:01-YQYVDDLYV and A*02:01-VIYQYVDDLYV were identified as optimal epitopes for the majority of study subjects. Viral replication of M184V HIV mutants was inhibited by CD8 T cell lines in vitro. In case of a failing lamivudine/emtricitabine containing regimen, individuals with a CD8 T-cell response toward M184V had a significant lower viral load than those without a CD8 response (p = 0.005). Two study subjects even achieved an undetectable viral load. Our data suggest that control of M184V mutant virus by CD8 T-cell responses is possible in vitro and in vivo. This control has important implications for therapeutic vaccination strategies.

Impact of changes in antigen level on CD38/PD-1 co-expression on HIV-specific CD8 T cells in chronic, untreated HIV-1 infection.

Excessive immune activation is a hallmark of chronic uncontrolled HIV infection. During the past years, growing evidence suggests that immune inhibitory signals also play an important role in progressive disease. However, the relationship between positive and negative immune signals on HIV-specific CD8 T cells has not been studied in detail so far in chronic HIV-1 infection. In this study, the expression of markers of positive (CD38) and negative (PD-1) immune signals on virus-specific CD8 T cells in chronic, untreated HIV-1 infection was evaluated using intracellular cytokine staining. Viral escape mutations were assessed by autologous virus sequence analysis and subsequent peptide titration assays. Single-epitope CD8 T-cell responses toward Gag, Pol, and Nef were compared in 12 HIV-1 controllers (viral load <5,000 cp/ml) and 12 HIV-1 progressors (viral load >50,000 cp/ml) and a highly significant increase of CD38/PD-1 co-expression on virus-specific CD8 T cells in progressors was found (P < 0.0001). The level of CD38/PD-1 co-expression was independent of epitope specificity. Longitudinal follow-up revealed a clear drop in CD38/PD-1 co-expression on virus-specific CD8 T cells after the suppression of antigen following either viral escape mutation or the initiation of HAART (P = 0.004). Antigen persistence with a fluctuating viral load revealed stable levels of CD38/PD-1 co-expression whereas significant rises in viral load were accompanied or even preceded by substantial increases in CD38/PD-1 co-expression. The CD38/PD-1 phenotype clearly distinguishes HIV-specific CD8 T-cell responses between controllers and progressors. Whether it plays a causative role in disease progression remains debatable. J. Med. Virol. 82:358-370, 2010. (c) 2010 Wiley-Liss, Inc.