Our primary hypothesis is that CCR5 inhibitors may have protective immunomodulatory effects independent of their impact on HIV replication. Specifically, we predict that maraviroc will reduce the persistent T cell activation that prevents normal immune reconstitution during HAART-mediated viral suppression. This hypothesis will be tested in the context of a placebo controlled pilot study assessing the impact of maraviroc in antiretroviral-treated patients with a CD4+ T cell count less than 350 cells/mm3. In order to address the immunologic activity of this drug independent of plasma HIV RNA levels, we will study individuals who have undetectable viral loads (< 75 copies RNA/mL). Subjects will be randomized to maraviroc for 24 weeks or matching placebo for 24 weeks, followed by a 12 week washout period. We will use as our primary endpoint the proportion of CD8+ T cells that co-expresses CD38 and HLA-DR, as these outcomes have been well validated in prior studies. The primary outcome will be change in the percentage of activated CD8+ T cells at week 24. Change in CD4+ T cell counts, HIV RNA levels (using ultra-sensitive techniques), and other more experimental immunologic measurements will be assessed as secondary outcomes.