Background:
Programmed cell death protein 1 (PD-1) is an immune checkpoint marker expressed on memory T cells and enriched in latently-infected CD4+ T cells and T follicular helper cells (TFH) containing replication-competent human immune deficiency virus 1 (HIV) provirus in people with HIV on antiretroviral therapy (ART). We recently tested a novel anti-PD-1 chimeric antigen receptor (CAR) T cell approach in vivo in simian immunodeficiency virus (SIV) mac239-infected and SIV-naïve rhesus macaques (RM) to assess the impact of PD-1 depletion on viral reservoirs and rebound dynamics. We found that anti-PD-1 CAR T cells expanded efficiently and rapidly eradicated all TFH cells from the germinal centers with concomitant depletion of detectable SIV RNA from this sanctuary site. This occurred even before release from ART. The anti PD-1 Car T cells persisted for up to 100 days concomitant with the depletion of PD-1+ memory T cells in blood and tissues, resulting in off target immune depletion and a marked increase in SIV replication in extrafollicular portions of lymph nodes, a 2-log higher plasma viremia relative to controls and accelerated disease progression, associated with the acute depletion of CD8+ memory T cells after CAR T expansion. The rapid depletion of TFH sanctuary site in GC while on ART offered the potential to an important advance in the quest for HIV cure if we could develop a second-generation product that had less off target long tern effects.
Methods:
Towards these ends, we integrated a Hepatitis C virus-derived non-structural protein 3 (NS3)-based ON switch into the intracellular domain of our anti-PD-1 CAR (NS3) T cell platform that can be controlled exogenously by administration of a NS3-specific protease inhibitor Grazoprevir (GZV).
Results:
Mechanistically, the NS3 domain undergoes autocleavage in absence of GZV, thus abrogating any CAR signaling and CAR T cell function. In vitro, primary T cells expressing the anti-PD-1 CAR NS3 kill PD-1+ cells and secret IFNg in presence of GZV in a dose-dependent manner indicating that the NS3 domain functions as an ON switch.
Conclusions:
Combined, these data indicate that a drug-controlled anti-PD-1 CAR NS3 is highly functional and can be controlled exogenously through administration or withdrawal of GZV. These data warrant further investigation of drug controlled-anti-PD-1 CAR T cells in ART-treated SIVmac239-infected rhesus macaques to transiently deplete TFH cells to determine their contribution to the latent reservoir.