Peripheral blood lymphocytes collected from normal volunteers were activated with human recombinant interleukin 2 and tested for LAK cell activity against the drug sensitive human breast carcinoma cell line MDA-MB-231, and its MDR-transfected variants MPAM-26, MPAHS-1-10, MPAHS-1-300, and MPAHS-DOX150. The gene discussed is IL2; the disease is breast carcinoma.