Single cell transcript analysis of human immunodeficiency virus gene expression in the transition from latent to productive infection.

In the lymph nodes of individuals infected with human immunodeficiency virus (HIV), there is evidence that points to three kinds of virus-cell relationships. Virions may be associated with CD4+ lymphocytes that are actively producing virus or may be bound at the surfaces of follicular dendritic cells like other antigens. HIV is also harbored in CD4+ lymphocytes and monocytes/macrophages in a latent form as transcriptionally silenced provirus. To ultimately investigate in vivo these and other HIV-cell interactions that play such critical roles in the persistence of virus, immune dysregulation, and depletion, we have developed an in situ hybridization method that discriminates multiply spliced from singly or unspliced viral transcripts. In this report we describe the method and the results obtained with it in an analysis of the switch from latent to productive infection of chronically infected T lymphocytes in culture. We found with this single-cell technique that there are two subpopulations in the culture, a minor one of productively infected cells and a major one of latently infected cells in which only low levels of viral transcripts terminated close to the 5' end of the viral genome were detected. Shortly after activation of viral gene expression with phorbol ester, transcripts encoding Tat and Rev increase in abundancy in individual latently infected cells and this is followed by increases in and cytoplasmic export of singly or unspliced mRNAs encoding structural proteins. These studies provide insights into the regulation of HIV gene expression from a single-cell perspective and, from that perspective, transcript profiles of productively infected cells as a frame of reference for defining HIV-cell relationships in individual cells in tissue sections.