We asked whether the cytotoxic capacity of CAR T cells was affected by PU.1 expression and monitored the upregulation of CD137, a surrogate maker for cytotoxicity associated with costimulation, in aCEA-28ζ-PU.1 CAR T cells compared to control CAR T cells after co-culture with CEA- 293T and CEA+ BxPC-3 cancer cells. Here, SPI1 is linked to cancer.