Abstract DP-003: TOWARD A HEMATOPOIETIC STEM CELL-BASED PROPHYLACTIC IMMUNO-GENE THERAPY APPROACH FOR OVARIAN CANCER

Our ultimate goal is to develop a long-lasting, cost-efficient, and technically simple approach that allows for the immuno-prophylaxis of cancer in patients with high-risk for disease recurrence and, ultimately, in patients with cancer-predisposing inherited mutations. Our approach is based on in vivo genetic modification of hematopoietic stem cells (HSCs). Because HSCs are self-renewing and give rise to all blood cell lineages, they provide a life-long source of transgene modified myeloid and lymphoid cells that, during tumor development, infiltrate the tumor and support tumor growth. Our in vivo HSC transduction approach involves subcutaneous injections of G-CSF/AMD3100 to mobilize HSCs from the bone marrow into the peripheral blood stream and the intravenous injection of an integrating, helper-dependent adenovirus (HD-Ad5/35++) vector system. In preliminary studies we used an integrating HDAd5/35++ vector expressing GFP and mgtmP140K under the ubiquitously active EF1a promoter. We demonstrated in adequate mouse models that HSCs transduced in the periphery home back to the bone marrow where they persist long-term. Transgene expression in peripheral blood cells can be achieved by O6BG/BCNU injection. Short-term exposure of in vivo transduced mice to low O6BG/BCNU doses resulted in stable GFP expression in 80% of peripheral blood cells and, in mice with implanted syngeneic tumors, in 80% of tumor infiltrating leukocytes. The predominant GFP-positive cell type in two syngeneic tumor models was tumor-associated neutrophils (TANs) (Ly6G+) and macrophages (TAMs) (F4/80+/MHCII+). GFP+ TANs and TAMs were detectable at very early stage of tumor development. To avoid adverse reactions using our in vivo HSC transduction/selection approach, the expression of therapeutic transgenes has to i) be localized to the tumor, ii) be automatically activated only when the tumor begins to develop, and iii) cease when the tumor disappears. To develop such an expression system, we determined (by miRNA-Seq and miRNA-array) the micro-RNA profile in GFP+ cells isolated from the bone marrow HSCs, spleen, PBMCs, and tumors of in vivo transduced mice. We found four miRNAs that were expressed at high levels in HSCs, splenocytes and PBMCs, but were absent in tumor-associated leukocytes. By inserting four copies of the corresponding target sites into the 39UTR of our GFP transgene, the corresponding mRNA is degraded in all cells except tumor-associated leukocytes allowing for tumor-restricted transgene expression. Studies on validating this system using GFP as a reporter gene are nearly completed. Furthermore, we have generated HDAd5/35++ vectors expressing scFv specific to mouse CTLA4 or PDL1 under miRNA control. We have performed in vivo HSC transduction-O6BG/BCNU treatment with these vectors and will implant syngeneic tumors at the beginning of August. We expect that intratumoral anti-CTLA4 or anti-PDL1 expression from TANs/TAMs at early stages of tumor development will overcome the immunosuppressive tumor environment allowing effector T-cells to stop tumor growth. The outcome of these studies will be presented. We have also started testing the prophylactic efficacy of our approach in oncogene-transgenic mice that develop spontaneous tumors. Citation Format: Chang Li, Paul Valdmanis, Andre Lieber. TOWARD A HEMATOPOIETIC STEM CELL-BASED PROPHYLACTIC IMMUNO-GENE THERAPY APPROACH FOR OVARIAN CANCER [abstract]. In: Proceedings of the 12th Biennial Ovarian Cancer Research Symposium; Sep 13-15, 2018; Seattle, WA. Philadelphia (PA): AACR; Clin Cancer Res 2019;25(22 Suppl):Abstract nr DP-003.