HIV-1-specific CD4+ T cells are qualitatively dysfunctional in the majority of HIV-1-infected individuals and are thus unable to effectively control viral replication. The current study extensively details the maturational phenotype of memory CD4+ T cells directed against HIV-1 and CMV. We find that HIV-1-specific CD4+ T cells are skewed to an early central memory phenotype, whereas CMV-specific CD4+ T cells generally display a late effector memory phenotype. These differences hold true for both IFN-γ- and IL-2-producing virus-specific CD4+ T cells, are present during all disease stages, and persist even after highly active antiretroviral therapy (HAART). In addition, after HAART, HIV-1-specific CD4+ T cells are enriched for CD27+CD28−-expressing cells, a rare phenotype, reflecting an early intermediate stage of differentiation. We found no correlation between differentiation phenotype of HIV-1-specific CD4+ T cells and HIV-1 plasma viral load or HIV-1 disease progression. Surprisingly, HIV-1 viral load affected the maturational phenotype of CMV-specific CD4+ T cells toward an earlier, less-differentiated state. In summary, our data indicate that the maturational state of HIV-1-specific CD4+ T cells cannot be a sole explanation for loss of containment of HIV-1. However, HIV-1 replication can affect the phenotype of CD4+ T cells of other specificities, which might adversely affect their ability to control those pathogens. The role for HIV-1-specific CD4+ T cells expressing CD27+CD28− after HAART remains to be determined.

Sexual contact with HIV-infected semen is a major driving force behind the global HIV pandemic. Little is known regarding the immune correlates of virus shedding in this compartment, although HIV-1-specific CD8+ T cells are present in semen. We collected blood and semen from 27 chronically HIV-infected, therapy-naive men without common sexually transmitted infections or urethral inflammation and measured HIV-1 RNA viral load and cytokine/chemokine levels in both compartments. HIV-1 RNA levels were 10-fold higher in blood than semen, but discordantly high semen shedding was associated with higher semen levels of the proinflammatory cytokines IL-6, IL-8, IL-12, and IFN-γ. Virus-specific CD8+ T cell epitopes were mapped in blood by IFN-γ ELISPOT, using an overlapping HIV-1 clade B peptide matrix, and blood and semen CD8+ T cell responses were then assayed ex vivo using intracellular IFN-γ staining. HIV-specific CD8+ responses were detected in 70% of semen samples, and their frequency was similar to or higher than blood. There was no correlation between the presence of virus-specific CD8+ T cells in semen and levels of HIV-1 RNA shedding. Among participants with detectable CD8+ IFN-γ semen responses, their relative frequency was not associated with reduced HIV-1 RNA shedding, and their absolute number was correlated with higher levels of HIV-1 RNA semen shedding (r = 0.6; p = 0.03) and of several proinflammatory cytokines. Neither the presence nor the frequency of semen HIV-specific CD8+ T cell IFN-γ responses in semen correlated with reduced levels of HIV RNA in semen.

In contrast to other viral infections such as CMV, circulating frequencies of HIV-1-specific CD4+ T cells in peripheral blood are quantitatively diminished in the majority of HIV-1-infected individuals. One mechanism for this quantitative defect is preferential infection of HIV-1-specific CD4+ T cells, although <10% of HIV-1-specific CD4+ T cells are infected. Apoptosis has been proposed as an important contributor to the pathogenesis of CD4+ T cell depletion in HIV/AIDS. We show here that, within HIV-1-infected individuals, a greater proportion of ex vivo HIV-1-specific CD4+ T cells undergo apoptosis compared with CMV-specific CD4+ T cells (45 vs 7.4%, respectively, p < 0.05, in chronic progressors). The degree of apoptosis within HIV-1-specific CD4+ T cells correlates with viral load and disease progression, and highly active antiretroviral therapy abrogates these differences. The data support a mechanism for apoptosis in these cells similar to that found in activation-induced apoptosis through the TCR, resulting in oxygen-free radical production, mitochondrial damage, and caspase-9 activation. That HIV-1 proteins can also directly enhance activation-induced apoptosis supports a mechanism for a preferential induction of apoptosis of HIV-1-specific CD4+ T cells, which contributes to a loss of immunological control of HIV-1 replication.