TRANSMISSIBILITY OF MURINE STEM-CELL VIRUS-BASED RETROVIRAL VECTORS CARRYING BOTH INTERLEUKIN-12 CDNAS AND A 3RD-GENE - IMPLICATIONS FOR IMMUNE GENE-THERAPY

The combination of immunotherapy With conventional treatments such as radio- and chemotherapy may be necessary to eradicate minimal residual disease. Interleukin 12 (IL-12) is a heterodimeric cytokine composed of two subunits, p40 and p35. Coordinate expression of the IL-12 p40 a nd p35 genes in several solid tumor models has been found to induce st rong and specific antitumor immune responses. In the interest of obtai ning high level IL-12 expression in leukemia/lymphoma cells for use as vaccines in cancer immunotherapy, we evaluated three IL-12 retroviral vector designs based on the murine stem cell virus (MSCV) vector whic h efficiently transduces functional genes into normal hematopoietic ce lls. MSCVpac-mIL-12 and MIPV-mIL-12 contain an encephalomyocarditis vi rus internal ribosome entry site for internal translation of bicistron ic mRNA transcripts, while MDCVpac-mIL-12 carries an expression casset te in the U3 region of the 3' long terminal repeat. We found that the MSCVpac-mIL-12 vector directed robust expression of both p40 and p35 g enes in several murine tumor cell lines of hematopoietic origin, inclu ding a T-cell lymphoma, a B-cell lymphoma, and a plasmacytoma/myeloma. In contrast, genomic instability or promoter interference hampered p4 0 gene expression in cells transduced with the MIPV-mIL-12 and MDCVpac -mIL-12 vectors, respectively. These findings provide the basis for th e design of IL-12 retroviral vectors for the treatment of hematologic malignancies in humans.