CD28 and acute myeloid leukemia: Accordingly, strong cytotoxic responses by NKp30-CD28 CAR TCRKO T cells to tumor cell lines representing AML and melanoma, not only in the presence of high B7H6 expression (HL60, K562) but also when B7H6 expression was intermediate (HEK-293T) or low (A375), were observed in vitro, which is in line with the previous finding that CAR T cell activation is facilitated by CD28 containing CARs in the presence of low antigen [45].