Vorinostat Renders the Replication-Competent Latent Reservoir of Human Immunodeficiency Virus (HIV) Vulnerable to Clearance by CD8 T Cells

Abstract

Latently human immunodeficiency virus (HIV)-infected cells are transcriptionally quiescent and invisible to clearance by the immune system. To demonstrate that the latency reversing agent vorinostat (VOR) induces a window of vulnerability in the latent HIV reservoir, defined as the triggering of viral antigen production sufficient in quantity and duration to allow for recognition and clearance of persisting infection, we developed a latency clearance assay (LCA). The LCA is a quantitative viral outgrowth assay (QVOA) that includes the addition of immune effectors capable of clearing cells expressing viral antigen. Here we show a reduction in the recovery of replication-competent virus from VOR exposed resting CD4 T cells following addition of immune effectors for a discrete period. Take home message: VOR exposure leads to sufficient production of viral protein on the cell surface, creating a window of vulnerability within this latent reservoir in antiretroviral therapy (ART)-suppressed HIV-infected individuals that allows the clearance of latently infected cells by an array of effector mechanisms.

Latent HIV reservoirs exhibit inherent resistance to elimination by CD8+ T cells

“…Both of those studies utilized clinical cell therapy products comprising mixed populations of expanded HIV-specific CD8 + T cells and activated natural killer (NK) and natural killer T (NKT) cells in combination with vorinostat, and reported reductions in viral outgrowth (14,73). The contrast between those results and that of our current study may be attributable to a number of factors, including the use of different immune effectors and methodological differences.…”

Very early antiretroviral therapy permits CD8 T cells to keep HIV reservoirs at bay

“…These results further indicate that effective HIV-specific CD8 T cells play an important role in the reduction of HIVproducing cells and more importantly latent reservoirs in patients receiving early ART. In these lines, use of latency reversing agents in vitro such as vorinostat has been shown to create a window of vulnerability by inducing production of viral protein on the cell surface allowing for subsequent clearance of latently infected cells by an array of effector mechanisms including ex vivo autologous CD8 T cells (26).…”

Targeting the Latent Reservoir for HIV-1

“…If latency reversal and CTL-mediated elimination are successful, fewer latently infected cells remain to produce viral outgrowth when plated at limiting dilution and maximally stimulated. This was indeed observed, and the effect was reversed with MHC-I blocking antibodies (Sung et al 2017). …”

“…An assay that measures presentation of HIV-1 epitopes by MHC Class I (MHC-I) on CD4 + T cells following latency reversal would facilitate the evaluation of LRA strategies. The latency clearance assay (LCA), pioneered by Margolis and colleagues, begins to address this issue (Sung et al 2015a; Sung et al 2015b; Sloan et al 2015; Sung et al 2017). Briefly, the LCA assay involves co-culturing CD8 + T cells or ex-vivo expanded HIV-1 specific CD8 + T cells (HXTCs) with autologous resting CD4 + T cells that have been pre-treated with the HDAC inhibitor vorinostat to induce latency reversal.…”

“…DARTS can mediate in vitro lysis of infected cells that are cultured with autologous CD8 + T cells (Sloan et al 2015; Petrovas et al 2017). Ex-vivo studies have also shown that DARTs can reduce viral outgrowth from the latent reservoir (Sung et al 2015b; Sung et al 2017). …”