Antileukemic activity of TNF-alpha gene therapy with myeloid progenitor cells against minimal leukemia

Tumor necrosis factor-alpha (TNF-alpha) has exhibited antitumor activity against a variety of tumors in rodents and human tumor xenografts in nude mice, but it has been only marginally effective in cancer patients because of dose-limiting toxicity associated with systemic TNF-alpha therapy. To circumvent toxicity and to test the antileukemic activity against quantitated minimal leukemia, we have cloned human TNF-alpha (HuTNF-alpha) gene in an advanced myeloid progenitor cell line. 32Dcl3 myeloid progenitor cells transfected with HuTNF-alpha cDNA by the retroviral supernatant infection method stably express HuTNF-alpha gene and secrete substantial amounts of HuTNF-alpha. When injected i.v. into irradiated mice, transduced cells could be detected in the marrow but not in spleen or liver 10-12 days later. Injection of 5 x 10(6) transduced cells produced no obvious symptoms of TNF-alpha toxicity (i.e., weight loss, cachexia, or fever) suggesting that TNF-alpha producing cells are well tolerated by the recipient mice. Coinjection of 5 x 10(6) transduced cells and 10(2) or 10(3) 32Dp210 leukemia (BCR/ABL+) cells resulted in inhibition of leukemia development by 10(2) but not 10(3) 32Dp210 cells. An equal dose of nontransduced 32Dcl3 cells was ineffective in inhibiting leukemia progression by 10(2) 32Dp210 cells. Mice that rejected leukemia were BCR/ABL oncogene negative 8 weeks after leukemia cell injection. These data demonstrate the potential for TNF-alpha gene therapy for destroying residual leukemia, without the toxicity of systemic TNF-alpha therapy, following cytoreductive therapy and bone marrow transplant.