Overexpression of c-Jun leads to multiple outcomes: increased production of IL-2 and IFNγ in CD19-28z CAR-T cells; IL-2-dependent increase in proliferation of both CD19-28z and CD19-BBz CAR-T cells; reduction in exhaustion markers; and increased efficacy of CAR-T cells in leukemia and osteosarcoma mouse models. The gene discussed is IL2; the disease is osteosarcoma.