Schematic illustrating the steps involved in characterizing the susceptibility of tissue-derived CD4+ T cells to HIV infection. Tonsils were processed into human lymphocyte aggregate cultures (HLACs), infected with an HIV-1 reporter virus, and then monitored for HIV entry after 2 hours or productive infection after 4 days. Using a variety of visualization, clustering, and statistical approaches, the susceptibility of different subsets of CD4+ T cells to HIV entry and productive infection was assessed, which led to the discovery of a new subset of memory CD4+ T cells highly susceptible to HIV entry but not productive infection. We are currently using these analytical approaches to characterize how HIV changes the properties of CD4+ T cells upon infection, including studies using patient cells.