To identify and study latently infected lymphoid-derived cells, we performed in vitro infection of tonsillar CD4+ T cells from HIV negative donors using the lentiviral vector HIVGKO (Figure 1A), pseudo-typed with an X4/R5 dual tropic HIV-1 envelope subtype B. In this model, purified CD4+ T cells are TCR-activated prior to infection with HIVGKO and evaluated 3 days after infection by flow cytometry to assess frequencies of productive and latent infected cells (Figure 1B). The gene discussed is CD4; the disease is infection.