An in vitro long-term tumor rechallenge assay showed that while CAR19/IL-15 NK cells from both Opt-Cs and Sub-Cs were equally effective at eliminating Raji cells (CD19 positive) after a single tumor challenge (Fig. 2a), CAR19/IL-15 NK cells from Sub-Cs lost their ability to control tumor growth upon rechallenge despite excellent viability. This evidence concerns the gene IL15 and neoplasm.