Finally, very low amounts of HMB-PP in conjugation with interleukin-2 (IL-2) confers human γδ T-cells with very potent anti-lymphoma/leukemia activity both in vitro and in a human/SCID mouse model for the transplantation of human tumors, thus attesting the therapeutic potential of HMB-PP for cancer immunotherapy. The gene discussed is IL2; the disease is leukemia.