Selective Depletion of Follicular Helper T Cells Using Chimeric Antigen Receptor Natural Killer Cells

Abstract Text: Hyperactivity of follicular helper T (Tfh) cells is a core feature of autoimmune disease and chronic infection. To date, no FDA-approved therapy exists for the selective depletion of Tfh cells, in part due to the lack of a specific cell-surface marker of these cells. While many immune cells express low levels of programmed cell death protein 1 (PD-1), Tfh cells express uniquely high levels of PD-1. To selectively deplete Tfh cells, our lab developed a chimeric antigen receptor (CAR) that endows effector cells with a potent capacity to selectively kill PD-1-high target cells. Conventional CAR ectodomains recognize target cells via high affinity single-chain variable fragments of antigen-specific antibodies, putatively killing targets that expresses any antigen. Our CAR uses the extracellular domain of programmed death-ligand 1 (PD-L1) that recognizes PD-1 with micromolar affinity, facilitating selective killing of targets with high but not those with intermediate or low surface expression of PD-1. Accordingly, we demonstrate that our PD-L1 CAR natural killer (NK) cells specifically kill PD-1-high Tfh cells while sparing other subsets of naïve, effector, and regulatory T cells with lower expression levels of PD-1. We validated CAR-mediated killing of PD-1-high target cells in multiple model systems. Mouse PD-L1 CAR T cells selectively killed PD-1-high splenic CD4 T cells in vitro and in vivo. PD-L1 CAR NK cells offer diverse applications for selectively depleting Tfh cells in contexts such as transplant rejection, allergy, lymphoma, autoimmune disease, and latent viral infection.