413. Pre-Clinical Preparation and Validation of Tumor Cell-Based IL-12 Immunotherapy for Acute Myeloid Leukemia

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Interleukin(IL)-12 is a potent pro-inflammatory cytokine that stimulates a variety of effector cells involved in anti-tumor immunity. Systemic administration of IL-12 has associated toxicities, however. Various strategies are being developed to reduce such toxicities by restricting IL-12 distribution. Options here include generating fusions with tumor-targeting molecules and directing gene delivery to specific cells. First – we used lentivirus vectors (LVs) to engineer expression of murine IL-12 in tumor cells ex vivo and subsequently infused such modified cells into recipient mice. This strategy restricts IL-12 to the local tumor microenvironment thereby promoting immune activation in the context of tumor-associated antigens (TAAs). Using mouse models of both leukemia and solid tumors, we found that this cell-based approach generated effective anti-tumor protection when as little as 1% of the tumor burden expressed IL-12 as long as threshold expression levels on a per cell basis were reached. Second – our groups showed that anti-tumor mechanisms here involve CD4+ killer T cells, dendritic cells, and direct cell-cell contact with effectors. Clinical translation of this cell-based IL-12 therapy is in progress in Toronto for AML using a novel LV to modify patients’ own blast cells. Patient AML cells collected to date (n = 21) were stratified based on in vivo growth kinetics and transduced with a near-GMP-grade bicistronic LV that encodes the human IL-12 cDNA as a p40-p70 fusion, as well as a mutant thymidylate kinase (tmpK) fused to the ectodomain of LNGFR (trLNGFR) as a suicide (cell-fate control) cassette. The trLNGFR/tmpK element allows selection and also selective ablation of transduced cells by administration of AZT. Furthermore, it also allows tracking of transduced cells and quantification of transduction frequencies/transgene expression levels. With our current protocol, functional transduction efficiencies of primary patient AML blasts ranged from 20% to 70% (n=17). Transduced AML cells displayed a strong correlation between vector copy number and trLNGFR/tmpK + IL-12 levels and dose-dependent sensitivity to AZT. In vitro immortalization (IVIM) assays determined that the near-GMP LV/IL-12 vector displayed minimal genotoxic risk in transduced lin- cells; insertion site analyses carried out on expanded clones displayed poly-to oligo-clonality patterns. Pre-clinical data on toxicity and scale-up considerations are being accumulated in preparation for a Clinical Trial Application to Health Canada targeting AML. This LV/IL-12 immunotherapy platform targeting tumor cells themselves thus holds potential to be effective against a wide variety of cancers.