IL7-IL15 fusion cytokine (fusokine)–secreting iPSC-derived mesenchymal stromal cells to convert immunosuppressive into highly immune-activated tumor microenvironments (TMEs), potentiate antitumor immunity, and synergize with PD-1 inhibition in ovarian cancer.

Abstract

e14522 Background: Mesenchymal stromal cells (MSCs) exhibit inherent tumor-homing properties and can be programmed to produce therapeutic proteins in situ (Andreeff M.Cancer Res. 2002, JNCI 2004, ASCO 2018). Methods: Here we reprogrammed adult dermal fibroblasts into induced pluripotent stem cells (iPSCs) using a synthetic, non-integrating mRNA transfection system. These iPSCs were stably modified to express interleukin-7 and interleukin-15 as fusion construct, prior to mesodermal lineage specification into MSCs (hereafter referred to as IL7-IL15-iMSCs). Results: Functionally, IL7-IL15-iMSCs secreted supraphysiologic levels of cytokines and induced potent CD8 and CD4 T cell activation (incl. CD25,pAKT,pS6, pSTAT5) and proliferation sustaining the long-term expansion of T cells in vitro and of macrophages in vivo, thus converting immune-suppressive MSCs into immune-activating cells. IL7/IL15-modified iMSCs induced ID8 tumor cell death in vitro in triple co-culture systems comprising iMSCs, and human PBMCs. In a syngeneic mouse model of ovarian cancer (ID8 and platinum-resistant ID8 cells in C57BL/6 mice), intraperitoneal administration of IL7-IL15-MSCs resulted in reduced tumor burden and extended survival of 58%. Immunohistochemical and CyTOF analyses revealed massive infiltration of activated T cells, macrophages, and other immune cells into the tumor microenvironment (TME) as well as enrichment of tumoricidal M1-type macrophages, with no detection of regulatory T cells, in contrast to controls. Remarkably, the combination of IL7-IL15 iMSCs combined with PD1 mAB in the ID8-Luc-Ova model resulted in 100% survival with no detectable tumor by BLI on day 160, relative to a median survival of 66 days in untreated controls, 75 days in IL7/IL15 iMSCs treated mice, 139 days inPD1 mAB. Intra-venously (IV) injected MSC in the orthotopic 4T1 triple-negative breast cancer model, six weeks post IL7-IL15-iMSC IV administration, showed robust iMSC engraftment in the TME, infiltration of immune cells and tumor reduction. Hence, IV injected iMSC also home to tumors. Conclusions: These data establish IL7/IL15-iMSCs as a novel, immunologically active stromal cell platform capable of remodeling the TME and amplifying both innate and adaptive anti-tumor responses. IL7-IL15 iMSC convert an immune-suppressive into an highly immune-activated TME in diverse tumor types. Combination of IL7/IL15 iMSC with PD1 mAB resulted in apparent cures in the ID8 ovarian cancer model. The scalability of iPSC-derived MSCs, combined with synthetic mRNA reprogramming and stable cytokine expression, renders this platform well-suited for clinical translation and a first clinical trial in ovarian cancer is under development.