Cord Blood‐Derived Fibroblast Activation Protein‐Targeted Chimeric Antigen Receptor Natural Killer Cells Persist in Vivo

Cancer-associated fibroblasts (CAFs) have been recognized as key contributors to tumor progression. Chimeric antigen receptor (CAR) T-cell therapy targeting fibroblast activation protein (FAP), a marker of CAFs, has gained attention and is being evaluated in both preclinical and clinical studies. Cord blood (CB)-derived CAR natural killer (NK) cell therapy has shown efficacy in hematologic malignancies. In this study, we generated FAP-targeting CAR NK cells (FAP-CAR NK cells). CD3-depleted CB mononuclear cells were stimulated with irradiated K562 cells expressing 4-1BB ligand (tumor necrosis factor ligand superfamily member 9) and membrane-bound interleukin-15 and interleukin-21 to expand NK cells, into which FAP-CAR was introduced. FAP-CAR NK cells produced cytokines and exerted cytotoxic activity when co-cultured with FAP-transduced HT1080 cells and CAFs isolated from human lung cancer tissue. In a xenograft model established by intrathoracic co-injection of A549 lung cancer cells and luciferase-expressing CAFs, injection of FAP-CAR NK cells, but not control CD19-CAR NK cells, resulted in their robust expansion and persistence in vivo for 5 weeks. However, CAFs were not eliminated by FAP-CAR NK cells, although CAR NK cells were clearly detected in the tumors. The levels of cytotoxicity-associated molecules (such as granzymes) were higher in FAP-CAR NK cells persisting in the spleens of mice compared with those in pre-infusion FAP-CAR NK cells. These results indicate that FAP-CAR NK cells have the potential to respond specifically to the target antigen and expand robustly in vivo, although further optimization is required to maintain cytotoxic function for a prolonged duration in vivo.