The present invention provides isolated cells that comprise, integrated into the genome of the cell, a transcription-competent immunodeficiency virus or a transcription-competent immunodeficiency virus-based retroviral vector. Under basal in vitro culture conditions, the immunodeficiency virus is latent, and the expression of the latent immunodeficiency virus can be reactivated. The invention farther provides methods of making a subject cell. The invention further provides screening methods for identifying agents that activate a latent immunodeficiency virus; and screening method for identifying agents that block reactivation of latent immunodeficiency virus expression in response to T cell activation signals. The invention further provides agents identified in the subject screening assays. The invention further provides methods of treating an immunodeficiency virus infection.