CD8+ TCR bias and immunodominance in HIV-1 infection

Immunodominance describes a phenomenon whereby the immune system consistently targets only a fraction of the available Ag pool derived from a given pathogen. In the case of CD8+ T cells, these constrained epitope-targeting patterns are linked to HLA class I expression and determine disease progression. Despite the biological importance of these predetermined response hierarchies, little is known about the factors that control immunodominance in vivo. In this study, we conducted an extensive analysis of CD8+ T cell responses restricted by a single HLA class I molecule to evaluate the mechanisms that contribute to epitope-targeting frequency and antiviral efficacy in HIV-1 infection. A clear immunodominance hierarchy was observed across 20 epitopes restricted by HLA-B*42:01, which is highly prevalent in populations of African origin. Moreover, in line with previous studies, Gag-specific responses and targeting breadth were associated with lower viral load set-points. However, peptide–HLA-B*42:01 binding affinity and stability were not significantly linked with targeting frequencies. Instead, immunodominance correlated with epitope-specific usage of public TCRs, defined as amino acid residue–identical TRB sequences that occur in multiple individuals. Collectively, these results provide important insights into a potential link between shared TCR recruitment, immunodominance, and antiviral efficacy in a major human infection

HLA-A*7401-mediated control of HIV viremia is independent of its linkage disequilibrium with HLA-B*5703.

The potential contribution of HLA-A alleles to viremic control in chronic HIV type 1 (HIV-1) infection has been relatively understudied compared with HLA-B. In these studies, we show that HLA-A*7401 is associated with favorable viremic control in extended southern African cohorts of >2100 C-clade-infected subjects. We present evidence that HLA-A*7401 operates an effect that is independent of HLA-B*5703, with which it is in linkage disequilibrium in some populations, to mediate lowered viremia. We describe a novel statistical approach to detecting additive effects between class I alleles in control of HIV-1 disease, highlighting improved viremic control in subjects with HLA-A*7401 combined with HLA-B*57. In common with HLA-B alleles that are associated with effective control of viremia, HLA-A*7401 presents highly targeted epitopes in several proteins, including Gag, Pol, Rev, and Nef, of which the Gag epitopes appear immunodominant. We identify eight novel putative HLA-A*7401-restricted epitopes, of which three have been defined to the optimal epitope. In common with HLA-B alleles linked with slow progression, viremic control through an HLA-A*7401-restricted response appears to be associated with the selection of escape mutants within Gag epitopes that reduce viral replicative capacity. These studies highlight the potentially important contribution of an HLA-A allele to immune control of HIV infection, which may have been concealed by a stronger effect mediated by an HLA-B allele with which it is in linkage disequilibrium. In addition, these studies identify a factor contributing to different HIV disease outcomes in individuals expressing HLA-B*5703

Human leukocyte antigen B*57 does not fully explain hepatitis C clearance in HIV controllers

ObjectiveHIV controllers demonstrate high rates of spontaneous clearance of hepatitis C virus (HCV) infection. The objective of this study was to evaluate the role of human leukocyte antigen (HLA) B*57 and other genetic polymorphisms on HCV clearance in HIV controllers.DesignThis is a prospective cohort study.MethodsPatients in the Study of the Consequences of Protease Inhibitor Era (SCOPE) were tested for anti-HCV using enzyme immunoassay (EIA3) and HCV RNA using discriminatory HCV transcription-mediated amplification assay (Norvatis). We compared the proportion of HIV controllers and noncontrollers demonstrating HCV clearance and fitted multivariable Poisson regression models with robust standard errors to estimate adjusted prevalence ratios (APRs) and assessed genetic and immunologic predictors of HCV clearance.ResultsOf 279 HIV/HCV seropositive individuals, 48 were HIV controllers. HIV controllers compared to HIV noncontrollers, were significantly more likely to have HLA B*57 (33 vs. 10%, P < 0.01). In multivariate analyses, adjusting for HLAB57, IL28B genotype, age, sex and race/ethnicity, HCV clearance was significantly more likely in HIV controllers than HIV noncontrollers [APR 1.78; 95% confidence interval (CI) 1.06-3.0; P = 0.03]. HLA B*57 did not explain the increased proportion of HCV clearance in HIV controllers, but IL28B CC genotype was independently associated with spontaneous HCV clearance (APR 2.76; 95% CI 1.85-4.11; P < 0.001).ConclusionAlthough enriched in HIV controllers, HLA B*57 does not explain the increased HCV clearance. Further identification of host immunologic or genetic factors that contribute to control of HIV and HCV may support the development of novel treatments for and effective vaccines against both viruses

Differential clade-specific HLA-B*3501 association with HIV-1 disease outcome is linked to immunogenicity of a single Gag epitope.

The strongest genetic influence on immune control in HIV-1 infection is the HLA class I genotype. Rapid disease progression in B-clade infection has been linked to HLA-B*35 expression, in particular to the less common HLA-B*3502 and HLA-B*3503 subtypes but also to the most prevalent subtype, HLA-B*3501. In these studies we first demonstrated that whereas HLA-B*3501 is associated with a high viral set point in two further B-clade-infected cohorts, in Japan and Mexico, this association does not hold in two large C-clade-infected African cohorts. We tested the hypothesis that clade-specific differences in HLA associations with disease outcomes may be related to distinct targeting of critical CD8(+) T-cell epitopes. We observed that only one epitope was significantly targeted differentially, namely, the Gag-specific epitope NPPIPVGDIY (NY10, Gag positions 253 to 262) (P = 2 × 10(-5)). In common with two other HLA-B*3501-restricted epitopes, in Gag and Nef, that were not targeted differentially, a response toward NY10 was associated with a significantly lower viral set point. Nonimmunogenicity of NY10 in B-clade-infected subjects derives from the Gag-D260E polymorphism present in ∼90% of B-clade sequences, which critically reduces recognition of the Gag NY10 epitope. These data suggest that in spite of any inherent HLA-linked T-cell receptor repertoire differences that may exist, maximizing the breadth of the Gag-specific CD8(+) T-cell response, by the addition of even a single epitope, may be of overriding importance in achieving immune control of HIV infection. This distinction is of direct relevance to development of vaccines designed to optimize the anti-HIV CD8(+) T-cell response in all individuals, irrespective of HLA type