Mechanisms involved in CD4 cell gains in HIV-infected patients switched to raltegravir

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Background:CD4+ gains in HIV patients on HAART result from release of T cells recently migrated from the thymus, redistribution from lymphoid tissues, proliferation in the periphery and/or reduced apoptosis. The relative contribution of each mechanism in CD4 restoration in patients with suppressed viremia switching antiretrovirals is unclear.Methods:HIV patients with undetectable viremia on HAART were identified at our clinic. A subset switched to raltegravir was compared with another group that kept therapy unmodified. Naive and memory CD4+ T-cells were measured by flow cytometry using CD45RA and CD27, respectively. Activation was examined using CD38 and recent thymic emigrants using CD31. Apoptosis was analyzed measuring soluble tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and Fas ligand (FasL).Results:Thirty-seven patients were examined, 19 switched to raltegravir and 18 controls, after a median of 26 months of suppressed viremia. At 6 months, mean CD4 cell counts significantly increased in raltegravir patients from 322 to 448 cells/μl (P = 0.026) but not in controls (from 312 to 330 cells/μl; P = 0.813). No significant changes were recognized in activation or CD31 expression in any group. In raltegravir patients, however, the proportion of naive CD4+ T cells significantly increased (P = 0.014) as well as CD38 expression in these cells (P = 0.036). A positive correlation was found between CD38 and CD31 expression in naive CD4+ T cells (R2 = 0.51, P < 0.001). TRAIL and FasL did not decline significantly in any group.Conclusion:HIV patients with prolonged undetectable viremia on HAART experience more pronounced CD4 gains after raltegravir switching than keeping the same regimen. An increased production of naive CD4+ T cells largely explains this effect.

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