CD28 and neoplasm: Nearly twice as many CD28-costimulated L1CAM-CAR T cells infiltrated (mean=196,839 T cells, range=190,276-201,389 cells) the tumor model compared to 4-1BB costimulated L1CAM-CAR T cells (mean=104,381 T cells, range: 87,304-129,403; Figure 1C).