IL2 and neoplasm: Early attempts to improve the antitumor activity of CAR T cells were based on the clinical use of IL-2 and IL-15 as anti-cancer immunotherapeutics, which as a monotherapy or in combination with adoptive transfer of tumor infiltrating lymphocytes (TILs) (64–66) had significant antitumor activity but were also associated with toxicity at higher doses (66–70).