Quantification of HIV infection and persistence in vivo

Jason M. Brenchley, Brenna J. Hill, David R. Ambrozak, David A. Price, Francisco J. Guenaga, Joseph P. Casazza, Janaki Kuruppu, Mario Roederer, Daniel C. Douek, and Richard A. Koup - Vaccine Research Center, NIAID, NIH, Bethesda (USA)

Background: HIV can infect non-dividing cells, but productive infection in vivo is facilitated by T-cell activation and/or proliferation. In vivo, CD4+ T-cells comprise many phenotypically and functionally distinct subsets. In addition, infection of different CD8+ T-cell populations has been suggested. A clear understanding of which T-cells harbor HIV in vivo and whether T-cell activation/proliferation increases their infection is critical to understanding persistence of HIV infection. Material and Methods: We utilized 11 parameter flow cytometry to define stringently and sort T-cell populations including naïve CD4+ and CD8+ T-cells, memory CD8+ T-cells, CD57- memory CD4+ T-cells (able to proliferate) and CD57+ memory CD4+ T-cells (unable to proliferate), and monocytes. We quantified and compared the amount of HIV DNA within each of these subsets by quantitative real-time PCR. Results: Memory CD4+ T-cells were found to be the most frequently infected subset with the CD57- memory subset being 10-fold more likely to be infected than the CD57+ memory subset.  Naïve CD4+ T-cells are infrequently infected, their infection occurs predominantly in the subset which have proliferated in vivo, and their infection does not correlate with infection of memory CD4+ T-cells or naïve CD8+ T-cells. CD8+ T-cells are infrequently infected and memory CD8+ T-cells are infected more frequently than naïve CD8+ T-cells. Infection of peripheral monocytes is rarely if ever found.  Investigation of pre- and post-integrated forms of HIV in these populations is ongoing, as are similar investigations in rhesus monkeys infected with SIV. Conclusions: The majority of HIV-infected CD4+ T cells in vivo are memory cells that can proliferate.  Infection of developing thymocytes is not likely to lead to a substantial pool of infected naive CD4+ and CD8+ T-cells. Infection of naïve CD4+ T-cells appears to occur during their ongoing turnover and infected naïve CD4+ T-cells do not become infected memory CD4+ T-cells. These two subsets are therefore infected under different conditions.  Infection of CD8+ T-cells is rare. While HIV is able to infect non-dividing cells, HIV predominantly infects T-cells that are undergoing activation and/or proliferation in vivo.  Infection of CD57-CD4+ T cells significantly alters their survival and likelihood of becoming CD57+CD4+ T cells.