KLRG1 and neoplasm: Although we are primarily concerned here with identifying improved costimulatory domains, it is important to note that the KLRG1 CAR is not simply a negative control but a potential tool to control CAR activity, and could be useful for reducing cytokine release syndrome, abrogating on-target off-tumor activation, and even generating post-translational oscillations in CAR activity that would mimic natural T cell receptor signaling dynamics.