CAR-engineered lymphocyte persistence is governed by a FAS ligand–FAS autoregulatory circuit

Chimeric antigen receptor (CAR)-engineered lymphocytes treat B cell malignancies; however, limited persistence can restrain the full therapeutic potential of this approach. FAS ligand (FAS-L)/FAS interactions govern lymphocyte homeostasis. Knowledge of which cells express FAS-L in patients with cancer and whether these sources compromise CAR persistence remains incomplete. Here, we constructed a single-cell atlas of diverse cancers to identify cellular subsets expressing FASLG, the gene encoding FAS-L. We discovered that FASLG expression is limited primarily to endogenous T cells, natural killer (NK) cells and CAR-T cells, while tumor and stromal cell expression is minimal. To establish whether CAR-T and CAR-NK cell survival is FAS-L regulated, we performed competitive fitness assays using FAS-dominant negative receptor (ΔFAS)-modified lymphocytes. Following transfer, ΔFAS-expressing CAR-T/CAR-NK cells became enriched, a phenomenon that mechanistically was reverted through FASLG knockout. By contrast, FASLG was dispensable for CAR-mediated tumor killing. In multiple models in female mice, ΔFAS coexpression enhanced antitumor efficacy. Together, these findings reveal that CAR-engineered lymphocyte persistence is governed by a FAS-L/FAS autoregulatory circuit.