Construction and characterization of a recombinant adenoviral vector expressing human interleukin-12

Interleukin-12 (IL-12) is a 70-kDa heterodimeric cytokine composed of a 35-kDa subunit (p35) and a 40-kDa subunit (p40). We have demonstrated previously that intratumoral delivery of a recombinant adenoviral vector expressing the mouse IL-12 gene significantly prolongs the survival time of mice with metastatic colon carcinoma in the liver. We now report the molecular cloning of cDNA for both subunits of human IL-12 (hIL-12) in a recombinant adenoviral vector in which the p40 and p35 subunits are linked and coexpressed using the encephalomyocarditis virus internal ribosome entry site. The recombinant adenoviral vector was used to transduce human tumor cell lines, and the presence of hIL-12 in the conditioned media was illustrated by enzyme-linked immunosorbent assay. The biological activity of hIL-12 in the conditioned media was also demonstrated in vitro through its ability to induce interferon-gamma production from peripheral blood mononuclear cells (PBMCs), to stimulate PBMC proliferation, and to enhance natural killer activity from normal human PBMCs to lyse natural killer-sensitive K562 target cells. The results of these studies support the application of this recombinant adenoviral vector construct as an efficient gene delivery vehicle in phase I/II clinical studies of hIL-12 gene therapy for cancer.