Functional impairment of T cells is characteristic of many chronic mouse and human viral infections. The inhibitory receptor programmed death 1 (PD-1; also known as PDCD1), a negative regulator of activated T cells, is markedly upregulated on the surface of exhausted virus-specific CD8 T cells in mice. Blockade of this pathway using antibodies against the PD ligand 1 (PD-L1, also known as CD274) restores CD8 T-cell function and reduces viral load. To investigate the role of PD-1 in a chronic human viral infection, we examined PD-1 expression on human immunodeficiency virus (HIV)-specific CD8 T cells in 71 clade-C-infected people who were naive to anti-HIV treatments, using ten major histocompatibility complex (MHC) class I tetramers specific for frequently targeted epitopes. Here we report that PD-1 is significantly upregulated on these cells, and expression correlates with impaired HIV-specific CD8 T-cell function as well as predictors of disease progression: positively with plasma viral load and inversely with CD4 T-cell count. PD-1 expression on CD4 T cells likewise showed a positive correlation with viral load and an inverse correlation with CD4 T-cell count, and blockade of the pathway augmented HIV-specific CD4 and CD8 T-cell function. These data indicate that the immunoregulatory PD-1/PD-L1 pathway is operative during a persistent viral infection in humans, and define a reversible defect in HIV-specific T-cell function. Moreover, this pathway of reversible T-cell impairment provides a potential target for enhancing the function of exhausted T cells in chronic HIV infection.

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Much uncertainty still exists over what T-cell responses need to be induced by an effective human immunodeficiency virus (HIV) vaccine. Previous studies have hypothesized that the effective CD8؉ T-cell responses are those driving the selection of escape mutations that reduce viral fitness and therefore revert posttransmission. In this study, we adopted a novel approach to define better the role of reverting escape mutations in immune control of HIV infection. This analysis of sequences from 710 study subjects with chronic C-clade HIV type 1 infection demonstrates the importance of mutations that impose a fitness cost in the control of viremia. Consistent with previous studies, the viral set points associated with each HLA-B allele are strongly correlated with the number of Gag-specific polymorphisms associated with the relevant HLA-B allele (r ‫؍‬ ؊0.56, P ‫؍‬ 0.0034). The viral set points associated with each HLA-C allele were also strongly correlated with the number of Pol-specific polymorphisms associated with the relevant HLA-C allele (r ‫؍‬ ؊0.67, P ‫؍‬ 0.0047). However, critically, both these correlations were dependent solely on the polymorphisms identified as reverting. Therefore, despite the inevitable evolution of viral escape, viremia can be controlled through the selection of mutations that are detrimental to viral fitness. The significance of these results is in highlighting the rationale for an HIV vaccine that can induce these broad responses.

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Previous studies have identified a central role for HLA-B alleles in influencing control of HIV infection. An alternative possibility is that a small number of HLA-B alleles may have a very strong impact on HIV disease outcome, dominating the contribution of other HLA alleles. Here, we find that even following the exclusion of subjects expressing any of the HLA-B class I alleles (B*57, B*58, and B*18) identified to have the strongest influence on control, the dominant impact of HLA-B alleles on virus set point and absolute CD4 count variation remains significant. However, we also find that the influence of HLA on HIV control in this C-clade-infected cohort from South Africa extends beyond HLA-B as HLA-Cw type remains a significant predictor of virus and CD4 count following exclusion of the strongest HLA-B associations. Furthermore, there is evidence of interdependent protective effects of the HLA-Cw*0401-B*8101, HLA-Cw*1203-B*3910, and HLA-A*7401-B*5703 haplotypes that cannot be explained solely by linkage to a protective HLA-B allele. Analysis of individuals expressing both protective and detrimental alleles shows that even the strongest HLA alleles appear to have an additive rather than dominant effect on HIV control at the individual level. Finally, weak but significant frequency-dependent effects in this cohort can be detected only by looking at an individual's combined HLA allele frequencies. Taken together, these data suggest that although individual HLA alleles, particularly HLA-B, can have a strong impact, HIV control overall is likely to be influenced by the additive effect of some or all of the other HLA alleles present.

A direct causal association between hepatitis B virus (HBV) infection and the development of nephropathy remains controversial. Epidemiological studies have shown that chronic carriage of HBV in some individuals (particularly children) leads to the development of nephrotic syndrome with a strong male predominance, the commonest histological type being membranous nephropathy (MN). Spontaneous clearance of HBV antigens (particularly the HBeAg) leads to abrogation of proteinuria. The isolation of immune complexes in the kidney suggests that the pathogenesis of the disease may have an immune-complex basis. Recent studies showing expression of HBV viral antigens in kidney tissue suggest direct viral-induced pathological alterations and chronic immunologic injury. Biosocial studies have detected no correlation between HBV carriage and proteinuria using both quantitative and qualitative urinary protein analysis. Genetic studies of HLA class I and II genes showed a predisposition to MN but no similar correlation in those with milder degrees of proteinuria. These findings suggest that milder proteinuria is unrelated to HBV carriage or genetic factors but the development of nephropathy, particularly MN, in patients with chronic HBV carriage (HBsAg and/or HBV DNA positive) is based on an interaction of virus and host factors. Although the natural history of the disease tends to remission with preservation of renal function, there is considerable morbidity and a small but significant mortality. Use of naturally occurring cytokines (such as interferon-α2b) and other candidate therapies accelerates clearance of the virus and proteinuria. The most effective tool in reducing the incidence of the disease is the use of HBV vaccines.