Targeted Reactivation of Latent HIV-1 Infection in T cells

O. Kutsch, D.N. Levy, G.M. Aldrovandi, J. Jones, E.N. Benveniste, G.M. Shaw.

University of Alabama at Birmingham, Birmingham (USA)

Background: Viral latency is a major obstacle to curative strategies for HIV-1 infection.  Estimates of the total body burden of latently infected T cells are in the range of only 10⁶, a small number that would seem therapeutically tractable by oncology standards.  Given recent successes in targeting human tumor cells using monoclonal antibodies, we sought to transfer this strategy and target latently HIV-1 infected cells.  In contrast to tumor therapy, or prevention of graft rejection following transplantation, where antibodies target and eliminate cells, reactivation of latent HIV-1 requires the specific activation of T cells, the natural cellular reservoir of latent HIV-1, without driving the cells into anergy or apoptosis.  Following reactivation, the infected cells will selectively succumb to the cytopathic effect of the virus or be eliminated by the immune system.  To this end, we introduce a novel strategy that allows for the targeted reactivation of latent HIV-1 in T cells by triggering CD28, a co-stimulatory molecule that is expressed exclusively on human T-cells.  For this purpose, we used an activating anti-CD28 antibody (clone 5D10) that, in contrast to the commonly used costimulatory anti-CD28 antibodies, stimulates T cells in the absence of TCR/CD3 stimulation. Results: Our data suggest that the potency of activating anti-CD28 antibodies to reactivate latent HIV-1 infection is three times higher than that of previously tested anti-CD3 antibodies, and does not result in T cell anergy or apoptosis.  Activating anti-CD28 antibodies could reactivate latent HIV-1 infection in a reporter cell line (J89GFP), and in latently infected thymocytes derived from HIV-1 infected (Thy/liv) SCID-hu mice, where a single antibody treatment reactivated latent HIV-1 with 60% of the efficiency of the phorbol ester PMA.  Reactivation was specific, as it could be blocked with costimulatory anti-CD28 antibodies but not by an isotype matched control antibody.  As reported for CD28-mediated T cell activation and proliferation, reactivation was found to be controlled by the MAPK p38 and ERK pathway. Conclusions: As CD28 is exclusively expressed on T cells, this approach combines a high degree of specificity for the natural cellular reservoir of latent HIV-1 with the potency to trigger the structural changes in the silent HIV-1 promoter required to reactivate the integrated virus, and could prove suitable to also reactivate latent HIV-1 in vivo.