Modified TALL-104 cells ATCC No. CRL 11386 characterized by cytotoxic activity in vitro and in vivo, irreversibly arrested cell proliferation, and the capacity to migrate in vivo to different tissue, wherein the TALL-104 cells are stimulated in vitro by treatment with one or a combination of the cytokines selected from the group consisting of IL-2 and IL-12 to enhance the cytotoxic activity of said TALL-104 cells against malignant cells, and .gamma.-irradiating the cells at a dose suitable to irreversibly arrest cell proliferation but not interfere with the cytotoxic activity in vitro and in vivo of the stimulated TALL-104 cells.