Background
The immune checkpoint marker programmed cell death protein 1 (PD-1) is commonly expressed on memory T cells and enriched in latently HIV-infected CD4+ T cells, including T follicular helper (TFH) cells. Chimeric antigen receptor (CAR) T cells are a cell-based technology that depletes cells expressing a target antigen. To determine whether CAR T cells can deplete reservoir-harboring, PD-1 expressing cells during ART, we previously tested anti–PD-1 CAR T cells in SIV-infected, ART-treated rhesus macaques. These CAR T cells expanded in vivo, depleted TFH cells, and reduced viral replication in germinal centers after interruption of ART. However, long-term CAR T cell persistence led to increased SIV replication in extrafollicular portions of lymph nodes and a loss of immunocompetence potentially due to CD8+ memory T cell depletion. These findings highlight the utility of CAR T cells in studying the SIV/HIV reservoir in this model to inform HIV cure interventions.
Methods
To enable repeated, temporary depletion of PD-1+ cells, we engineered a novel CAR using a Hepatitis C virus protease NS3-based ON switch (anti-PD-1 CAR NS3), allowing control of cytotoxic activity and cytokine secretion via administration of an NS3 protease inhibitor (grazoprevir; GZV) in vitro. This system enables investigation of “pulse therapy,” a strategy involving repeated reservoir-targeting cycles alternating with CAR T cell inactivity to promote immune reconstitution.
Results
We tested pulse therapy in an adoptive transfer pilot study using a SIV-naïve rhesus macaque that received anti-PD-1 CAR NS3 T cells and two GZV courses, separated by a 2-week washout phase. During the first GZV course, anti-PD-1 CAR NS3 T cells expanded in vivo, without a noticeable decrease in PD-1+ cell frequency in peripheral blood. CAR T cells proliferated vigorously (up to 80% Ki67+ by day 14) and trafficked to lymphoid tissues and lungs. However, during the second GZV course, CAR T cells did not re-expand and remained at low frequency. Pharmacokinetic analyses of GZV and further studies on CAR function indicated that the GZV drug levels were insufficient to achieve complete CAR T cells functionality and that anti-PD-1 CAR NS3 T cells are more reliant on exogenous interleukin-2 than the original CAR.
Conclusions
These data suggest that pharmacological control of anti-PD-1 CAR NS3 T cells is achievable; however, further refinement is required to optimize pulse therapy for effectively studying SIV/HIV reservoir dynamics during ART.
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