CD28 and neoplasm: Second generation murine mCD19 CAR T cells containing CD3ζ and CD28 costimulatory domains19 exhibited potent cytotoxicity against the engineered B16-TR-mCD19 cell line in co-culture assays at effector-to-tumor (E:T) ratios of 0.5 and higher as measured by bioluminescence imaging (p < 0.0001; n = 3 for each condition) (Figure 1A).