281. Engineering Hematopoiesis for Tumor-Targeted Interferon-alpha Delivery Inhibits Multuple Myeloma and B Cell Malignancies

A protective and immunosuppressive tumor microenvironment is considered a key factor for the failure of anti-cancer treatments. We developed a strategy to turn a pro-tumoral into an anti-tumoral microenvironment by transplanting genetically engineered hematopoietic stem/progenitor cells (HSPC). We exploit a transcriptionally and post-transcriptionally regulated Interferon-alpha (IFNa) cassette to drive specific expression of this pleiotrophic antitumor cytokine in tumor-infiltrating monocytes/macrophages (IFNa gene therapy). When applied to spontaneous mouse or orthotopic human breast cancer models, IFNa gene therapy with mouse or human HSPC, respectively, inhibited tumor and metastases growth by activating innate and adaptive immune cells in the tumor (Escobar et al, Sci Transl Med 2014). To test this approach in clinics, we aim for a first-in-human trial of IFNa gene therapy in patients undergoing autologous transplantation, a procedure widely practiced for Multiple Myeloma (MM) and Lymphoma. To detect potential untoward effects of chronic IFNa exposure on human hematopoiesis, we transduced mobilized peripheral blood CD34+ cells with the human IFNa lentiviral vector (LV). A single round of transduction yielded vector copy numbers (VCN) of 0.4 to 4 according to the protocol used, with 30-90% transduction efficiency and 1-4 VCN per cell. This IFNa-engineered graft was mixed with mock-transduced CD34+ cells in various proportions and transplanted into NSG mice. All mice engrafted and showed long-term, multilineage hematopoietic output, with a dose-dependent decrease in the human graft at high, supratherapeutic VCN. To explore the efficacy of IFNa gene therapy on MM, we intravenously injected NSG mice reconstituted with IFNa LV-transduced CD34+ cells (VCN:1-3; chimerism 20-50%) with the human MM.1S cell line and followed MM growth by bioluminescence imaging and serial blood and BM exams. IFNa gene therapy strongly delayed myeloma bone disease and improved survival (9 wks vs. 13 wks median survival, p=0.03). Moreover, we tested the efficacy of IFNa gene therapy on human primary Ph+ B-ALL blasts as a model of high-grade B cell malignancies. Strikingly, IFNa gene therapy substantially reduced B-ALL growth in NSG and NSG3GS mice (p=0.002 and p=0.015), and Imatinib treatment, the standard of care for Ph+ALL, gave an additive effect when combined with IFNa gene therapy. These encouraging results pave the way for a phase I/II trial in patients with MM or B cell malignancies. To better understand the mechanism of IFNa gene therapy, we are setting up immuno-competent mouse models of MM and lymphoid malignancies. We developed a spontaneous model of high grade B cell leukemia/lymphoma based on ectopic expression of miR-126. IFNa gene therapy significantly reduced leukemic burden. Moreover, we derived more immunogenic leukemic subclones engineered with the ovalbumin or huCD20 antigen. These lines will help defining the immunomodulatory effect of IFNa gene therapy and allow testing combination with monoclonal antibodies or adoptive T cell transfer.