The HIV reservoir – that fraction of the virus that persists despite taking antiretroviral therapy – exists largely in CD4+ T memory cells. Emerging evidence suggests that the proportion of the reservoir that resides in different subsets of CD4+ T cells – central, transitional, effector, naïve, memory stem cells - may vary between patients. The subsets of CD4+ T cells in which the reservoir predominates in turn can influence the size of the total reservoir. This study will investigate which subsets constitute the major fraction of the reservoir and whether this changes over the course of the infection or with the stage of infection at which antiretroviral therapy is initiated. Understanding the dynamics of the reservoir may shed light on whether strategies to directly target various subsets of CD4+ T cells may be a productive strategy to cure HIV.