Augmented HIV-specific interferon-gamma responses, but impaired lymphoproliferation during interruption of antiretroviral treatment initiated in primary HIV infection.

BACKGROUND: Antiretroviral therapy (ART) introduced during primary HIV infection followed by treatment interruption (TI) is postulated to enhance virologic control through induction of HIV-specific CD4 T cells, which foster virus-specific CD8+ T cells that suppress virus replication. This hypothesis was evaluated in 21 subjects enrolled in AIDS Clinical Trials Group 709, a substudy of AIDS Clinical Trials Group 371, which prospectively evaluated subjects who received ≥1 year of ART initiated in acute or recent HIV infection followed by TI. METHODS: Lymphoproliferation was assessed by [methyl-H] thymidine incorporation and HIV-specific CD8+ T-cell interferon-gamma responses by enzyme-linked immunospot-forming assays. Virologic success was defined as sustained viral load <5000 copies per milliliter for 24 weeks after TI. RESULTS: HIV-specific lymphoproliferative responses were detected at least once in 5 (24%) of 21 subjects, were generally transient, and were unrelated to HIV-specific interferon-gamma responses (P > 0.4). HIV-specific CD8+ interferon-gamma responses increased after 48 weeks of ART (P = 0.03), but failed to predict virologic success (P = 0.18). Compared with seronegative subjects, lymphoproliferation to Candida, cytomegalovirus, and alloantigens was similar in HIV-infected subjects during ART, but lower during TI (P ≤ 0.04). CONCLUSIONS: HIV-specific CD8+ T-cell interferon-gamma responses expand during ART following primary HIV infection, but are not related to HIV-specific lymphoproliferative responses nor virologic success. Impaired non-HIV antigen-specific lymphoproliferation associated with TI suggests this strategy could be deleterious.

Phenotypic and functional characterization of HIV-1-specific CD4+CD8+ double-positive T cells in early and chronic HIV-1 infection.

OBJECTIVE: CD4+CD8+ double-positive (DP) T cells represent a poorly characterized population of effector T cells found at low frequencies in the peripheral blood. Virus-specific DP T cells have been identified in HIV-1-infected patients but their origin, relationship to conventional CD4+ and CD8+ single-positive (SP) T cells, and role in disease pathogenesis are unclear. METHODS: In this study, peripheral blood T cells were analyzed for cytokine production, maturation, and cytolytic marker expression by polychromatic flow cytometry in subjects with both early (n = 27) and chronic (n = 21) HIV-1 infection. RESULTS AND CONCLUSIONS: HIV-1-specific interferon gamma (IFN-g)-producing DP T cells were identified at a median frequency of 0.48% compared with 1.08% and 0.02% for CD8 and CD4 SP cells, respectively, in response to pooled HIV-1 peptides. HIV-1- specific DP T cells exhibited polyfunctionality with characteristics of both CD4 and CD8 SP T cells, including coproduction of IFN-gamma and IL-2 and expression of cytolytic-associated lysosomal-associated membrane protein. No differences in frequencies of unstimulated DP T cells were observed in early compared with chronic infection. However, chronic infection was associated with higher frequencies of HIV-specific, IFN-gamma-producing DP T cells and higher fractions of effector memory and lysosomal-associated membrane protein expression among these cells, suggesting an effect of cumulative viral antigen burden on DP T-cell function.

SDF-1alpha is a potent inducer of HIV-1-Specific CD8+ T-cell chemotaxis, but migration of CD8+ T cells is impaired at high viral loads.

Multiple impairments in HIV-1-specific cytotoxic T cells (CTL) have been reported, but derangements in HIV-1-specific CD8+ T-cell chemotaxis have not been described previously. We assessed migration to SDF-1alpha (stromal cell-derived factor 1-alpha) and CX3CL1 in vitro and expression of cognate receptors, CXCR4 and CX3CR1, by flow cytometry in peripheral blood and lymph node CD8+ T cells from HIV-1-seropositive and -seronegative individuals. Compared with seronegative individuals, percentages of CXCR4+CD8+ T cells were reduced (median, 26% versus 74%, p < 0.001) and percentages of CX3CR1+CD8+ T cells were increased (median, 33% versus 15%, p = 0.03) in seropositive individuals. Robust migration of peripheral blood mononuclear cell (PBMC) CD8+ T cells to SDF-1alpha (1 alphag/ml) was observed in both HIV-1-seropositive (median chemotactic index [CI] 4.9) and -seronegative (median CI 2.8) subjects (p = 0.46). CI to SDF-1alpha was not significantly related to percentage of CXCR4+CD8+ T cells or density of CXCR4, but correlated inversely with plasma HIV-1 RNA concentration (r = -0.82, p = 0.03). Little chemotaxis was observed in response to CX3CL1 and it was unrelated to CX3CR1 expression. Lymph node CD8+ T-cell chemotaxis to SDF-1alpha and CX3CL1 in four subjects demonstrated the same patterns observed in PBMC. HIV-1-specific tetramer-staining CD8+ T cells exhibited chemotaxis of similar magnitude as PBMC CD8+ T cells in a subset of subjects. These data suggest that SDF-1alpha is a potent chemoattractant for HIV-1-specific CTL, but that impairments in migration of HIV-1-specific CTL may exist at high viral loads. Improved understanding of the determinants of CTL localization may provide insight into novel therapies to enhance delivery of CTL to sites of HIV-1 replication.

CTL fail to accumulate at sites of HIV-1 replication in lymphoid tissue.

The inability of HIV-1-specific CTL to fully suppress virus replication as well as the failure of administration of exogenous CTL to lower viral loads are not understood. To evaluate the hypothesis that these phenomena are due to a failure of CTL to localize at sites of HIV-1 replication, we assessed the distribution of HIV-1 RNA and HIV-1-specific CTL identified by HIV-1 peptide/HLA class I tetrameric complexes (tetramers) within lymph nodes of 14 HIV-1-infected individuals who were not receiving antiretroviral therapy. A median of 0.04% of follicular compared with 0.001% of extrafollicular CD4(+) cells were estimated to be producing HIV-1 RNA, a 40-fold difference (p = 0.0001). Tetramer-stained cells were detected by flow cytometry in disaggregated lymph node cells from 11 subjects and constituted a significantly higher fraction of CD8(+) cells in lymph node (mean, 2.15%) than in PBMC (mean, 1.52%; p = 0.02). In situ tetramer staining in three subjects' lymph nodes, in which high frequencies of tetramer-stained cells were detected, revealed that tetramer-stained cells were primarily concentrated in extrafollicular regions of lymph node and were largely absent within lymphoid follicles. These data confirm that HIV-1-specific CTL are abundant within lymphoid tissues, but fail to accumulate within lymphoid follicles where HIV-1 replication is concentrated, suggesting that lymphoid follicles may be immune-privileged sites. Mechanisms underlying the exclusion of CTL from lymphoid follicles as well as the role of lymphoid follicles in perpetuating other chronic pathogens merit further investigation.