153 Modeling HIV-1 Latency in vitro

Abstract

The human immunodeficiency virus type-1 (HIV-1) establishes latency primarily by infecting activated CD4+ T cells that later return to quiescence as memory cells. Latency allows HIV-1 to evade immune responses and to persist during anti-retroviral therapy. The lack of a valid cellular model to study HIV-1 latency has hindered advances in the understanding of its biology. We developed an in vitro model suitable to investigate the induction, maintenance and reactivation of HIV-1 latency. Our system recapitulates the events of primary and secondary antigen-driven immune responses in which CD4+ T cells are activated with dendritic cells and antigen, infected in vitro with HIV-1, and then brought back to quiescence through a resting phase in the presence of interleukin-7. During the resting phase, the latently infected cells generated in vitro with our system lack expression of activation markers; do not undergo cellular proliferation and do not sustain viral replication. All these activities resume promptly following secondary antigen stimulation. This system is suitable to study the biology of HIV-1 latency. Indeed, we have performed microarray analyses with RNA isolated from FACS-sorted, quiescent, latently infected vs. uninfected cells. The results suggest that HIV-1 achieves latency in CD4+ T cells not as a consequence of the host cell's ability to survive clonal contraction and to establish immunological memory. Rather, HIV-1 appears to “re-program” the host cell's gene expression profile in a way that promotes cell quiescence, supports cell survival and thus induces viral latency. In addition, a panel of genes encoding for cell surface molecules is differently expressed in latently infected vs. uninfected cells, which may have diagnostic and therapeutic implications. The results of these analyses point to important new concepts regarding the establishment and maintenance of latency in CD4+ T cells, and thus suggest new mechanisms of viral persistence in HIV-1 patients.