Evaluation of γ-retroviral vectors that mediate the inducible expression of IL-12 for clinical application

The clinical application of interleukin 12 (IL-12) has been hindered by the toxicity associated with its systemic administration. To potentially overcome this problem, we developed a promoter designed to direct IL-12 expression within the tumor environment using an inducible composite promoter containing binding motifs for the nuclear factor of activated T cells (NFAT) linked to a minimal IL-2 promoter. In this study, the NFAT promoter was coupled to a single-chain human IL-12 gene and inserted into two γ-retroviral self-inactivating (SIN) vectors (SERS.NFAT.hIL12, and SERS.NFAT.hIL12.PA2) and one γ-retroviral vector (MSGV1.NFAT.hIL.12 PA2). Peripheral blood lymphocytes (PBLs) were double transduced with an antigen specific T cell receptor and the three NFAT.hIL12 vectors. Evaluation of inducible IL-12 expression, transduction efficiency, and vector production considerations, led to the choice of the MSGV1.NFAT.hIL12.PA2 vector for clinical application. MSGV1.NFAT.hIL12.PA2 PG13 retroviral vector producer cell clones were screened by transduction of tumor antigen specific PBLs. Based on expression studies in PBL, clone D3 was chosen to produce clinical-grade viral vector supernatant and was demonstrated to efficiently transduce young TIL. The vector-transduced young TIL with known tumor recognition demonstrated specific inducible IL-12 production following co-culture with HLA-matched tumor targets and had augmented effector function as demonstrated by increased IFN-γ secretion. These results support the clinical application of adoptive transfer of young TIL engineered with the NFAT.hIL12 vector as a new approach for cancer immunotherapy.