IL15 and neoplasm: Interestingly, in the Panc02-claudin 18.2 tumor model in which approximately 10% original tumor cells are negative for CLDN18.2 expression, we observed that some mice treated with H9 CAR-IL15 T cells eventually had relapsed tumor that lacked CLDN18.2 expression, indicating the occurrence of immune escape via selection of antigen-negative cells under continuous CAR-T-cell immune pressure, which is consistent with previous reports of IL-15-modified engineered T cells in human xenograft models (15, 27, 33).