CD28 and atrial fibrillation: In contrast, the hIgGFc spacer domain used in previously generated antifungal CAR T-cells (14) might be more susceptible to clearance by Fc receptors (29); (iii) the CD137/4-1BB costimulatory domain was selected based on its potential clinical benefits of improved persistence, enhanced proliferation, and lower propensity to induce immunotoxicity compared with the previously used costimulatory molecule CD28 (30, 31); and (iv) our AF-CAR T cells were generated using an LV vector system that could accelerate the generation of clinical-grade AF-CAR T cells.