S912 LOCAL INTERFERON‐ALPHA DELIVERY INTO THE MYELOMA MICROENVIRONMENT BY GENE‐ENGINEERED AUTOLOGOUS STEM CELL TRANSPLANTATION
Authors: G. Antonarelli, A. Mucci, G. Escobar, G. Desantis, F. M. Vittoria, A. Capotondo, L. Naldini, F. Ciceri, B. Gentner
Journal: HemaSphere (2019)

Background: Multiple Myeloma (MM) is an incurable malignancy heralded by an immunosuppressive Tumor Microenvironment (TME). Therapeutic attempts aiming at reprogramming the TME and unleashing innate and adaptive immunity may synergize with current anti‐MM drugs, deepen responses and ultimately prolong long‐term survival. Aims: We developed an ex vivo Gene Therapy (GT) approach that locally delivers Interferon‐alpha (IFNa) into the TME through the Tie2+ myeloid progeny of transplanted gene‐modified Hematopoietic Stem and Progenitor Cells (HSPCs). Methods: Murine Lin‐ or human Cord Blood (huCB) HSPCs were transduced with lentiviral vectors (LV) expressing, respectively, murine or human IFNa under transcriptional control of the Tie2 promoter and post‐transcriptional control by miR‐126–3p thereby targeting IFNa expression to a subset of tumor‐infiltrating monocytes. IFNa‐LV‐transduced or mock‐transduced HSPC were transplanted into Vk∗Myc transgenic mice after they have spontaneously developed a serum M‐spike (immunocompetent mouse model) or into NSGW41 mice that were successively challenged with a luciferase+ MM.1S human myeloma cell line (human xenograft model). Myeloma disease progression was monitored by serum protein electrophoresis (Vk∗Myc), whole body bioluminescence imaging (MM.1S) and bone marrow plasma cell burden at the endpoint. In the MM1.S model, IFNa‐GT was combined with systemic Daratumumab (i.p.), Lenalidomide (i.p.) and Carfilzomib (i.v.) treatment. Results: In the spontaneous Vk∗Myc mouse model of myeloma, Ifna GT halted myeloma progression (4 months PFS of 58.3% vs. 15.8% in control) and reduced mortality by &gt;50%. Treatment response was associated with a higher proportion of CD8+ T cells in the BM and seen at donor cell chimerism as low as 4%. Mechanistic studies on the tumor microenvironment are ongoing. The NSGW41 xenograft model transplanted with huCB HSPCs allowed the development of a larger and more diverse human myeloid compartment compared to the classical NSG model. Even in the absence of adaptive immunity, IFNa‐GT resulted in a significant reduction in BM myeloma burden (13.4+/‐2.2% vs. 26.3+/‐3.7% in mice transplanted with control huCB cells; n = 19 vs. 18), independently confirmed by BLI. Interestingly, the IFNa‐GT group showed an increased content of human CD33+ HLA‐DR+ CD11c+ dendritic cells (including a pro‐inflammatory SLAN+ subset) and increased levels of CD16 and HLA‐DR expression on human myeloid cells within the myeloma‐bearing BM, suggestive of myeloid cell reprogramming towards a more immune‐stimulatory state. Moreover, IFNa‐GT induced an upregulation of CD38 expression (on average 1.4 fold on myeloma cells). This provides a rationale for combining IFNa‐GT with other anti‐MM drugs. Indeed, the anti‐MM effect of Daratumumab, Lenalidomide or Carfilzomib was enhanced by IFNa‐GT, without excessive toxicity on the HSPC graft. Summary/Conclusion: Our studies conducted both in the immunocompetent Vk∗Myc murine model as well as in the hematochimeric xenotransplantation setting demonstrate that IFNa‐GT has robust anti‐MM effect and may subvert the immunosuppressive MM TME, acting both on myeloma cells as well as on the immune infiltrate. A phase I/II dose‐escalation study of IFNa‐GT in patients with early‐relapsed multiple myeloma has recently been approved and is starting accrual in March 2019.