Construction of a recombinant adeno-associated virus (rAAV) vector expressing murine interleukin-12 (IL-12)

Abstract

IL-12 is a heterodimeric cytokine that is known to induce tumor regression and long-term antitumor immunity. Recombinant adeno-associated virus (rAAV) vectors are advantageous for gene therapy in that they lack pathogenicity in humans, infect dividing as well as nondividing cells, and show a broad range of infectivity. We constructed an rAAV vector expressing interleukin-12 (IL-12) for cancer immunotherapy studies in a mouse model by inserting murine IL-12 (mIL-12) p35 and p40 cDNAs into the plasmid pRep4 and inserting the encephalomyocarditis virus internal ribosomal entry site between the p35 and p40 cDNAs. The mIL-12 expression cassette containing the Rous sarcoma virus promoter and a simian virus 40 polyadenylation signal was subcloned into the AAV plasmid p008Sub/NeoR, which contains two AAV inverted terminal repeat sequences and the NeoR gene driven by the thymidine kinase promoter. rAAV virions (10⁴ infectious particles/ml) were generated by cotransfection of rAAV-mIL-12 and a helper plasmid (pAAV/Ad) into 293 cells previously infected with adenovirus 5. After infection of D6 fibroblasts with rAAV-mIL-12, G418-resistant clones were isolated. Each of the 1D D6 clones isolated produced up to 5.2 ng/10⁶ cells/48 hours of mIL-12 as determined by enzyme-linked immunosorbent assay. Induction of interferon-γ, enhanced lymphocyte proliferation, and cytotoxicity assays confirmed biologically functional IL-12 production by the vector. This is the first report indicating that an rAAV vector expresses mIL-12, which can be used to model the effects of mIL-12 alone and/or in combination with other antitumor agents.