Dendritic cells (DC) that have been genetically modified to express
cytokine genes may be novel tools for inducing antitumor immune responses. In the present study, the pMX retroviral vector was modified to express the mouse
IL-2 (mIL-2pMX) and mouse
IL-12 (mIL-12pMX) genes. Supernatants from 293 cells transfected with pMX retroviral vectors were harvested and used to transduce mouse lin- bone marrow (BM) progenitor cells. After 48 h co-culture with pseudotype retrovirus, BM cells were cultured for 12 days in the presence of mGM-CSF, mSCF and mTNF-alpha to obtain a DC-enriched fraction. Flow cytometric analysis showed that GFP
protein expression in these cultures was 20-40% and that 40-50% of the cultured BM cells were positive for the DC marker, DEC205. About 60% of cells sorted for DEC205 also expressed GFP. The supernatants of DC-mIL-2 and DC-mIL-12 cultured for 48 h contained 5.2 +/- 0.15 and 33.9 +/- 2.6 ng
cytokine protein per milliliter, respectively. Intratumoral injection of DC-mIL-2 or DC-mIL-12 on days 8 and 15 after the
intradermal injection of 1 x 105 B16F10 cells, resulted in a significant reduction in
tumor size by day 21, as compared with mice treated with unmodified DC or DC-GFP. Longer term analysis as assessed at day 42 revealed that B16
tumor-bearing mice treated with
cytokine gene-modified DC survived significantly longer than mice from other groups. Spleen cells obtained from DC-treated mice were specifically sensitized for the generation of CTL by subsequent restimulation with gene-modified DC. These results suggested that DC genetically modified to express
IL-2 or
IL-12 can induce potent antitumor responses against well-established, poorly immunogenic B16F10
tumors. Gene Therapy (2000) 7, 2113-2121.