Background: We previously discovered that bone marrow derived Mesenchymal stromal cells (BM-MSCs) migrate to the stroma of numerous cancers and their metastases, forming tumor-associated fibroblasts (TAFs) and can be modified to secrete proteins within the tumor microenvironment (TME). MSCs have not been utilized extensively in cancer therapy due to their immunosuppressive properties, limited replicative capacity, and variable quality depending on the source.

Methods: Here, we report the characterization of induced mesenchymal stromal cells (iMSCs) derived from pluripotent stem cells (iPSCs), which were uniquely generated from adult skin fibroblasts using a transient mRNA transfection technique. Notably, iMSCs demonstrated superior proliferative capacity under both normoxic and hypoxic conditions, while preserving their trilineage differentiation potential. Comprehensive molecular profiling, including RNA sequencing, single-cell mass cytometry (CyTOF), and Luminex assays, revealed strong phenotypic and functional similarities between iMSCs and BM-MSCs. Crucially, no evidence of sarcoma formation was observed in NSGS mice following intraperitoneal, subcutaneous, or intravenous administration of iMSCs, highlighting their robust safety profile. We engineered a DNA cassette into these cells to enable constitutive superphysiological expression of interleukin(IL)-7 and IL-15, expressed as either individual molecules (P2A) or a single fused molecule (FUS). Both, P2A and FUS iMSCs demonstrate the capacity to drive T cell proliferation autonomously in co-culture experiments.

Results: IL7/IL15-modified iMSCs induced tumor cell death in a triple co-culture system comprising iMSCs, the ovarian cancer cell line ID8, and human PBMCs. In a syngeneic mouse model of ovarian cancer (ID8 cells in C57BL/6 mice), intraperitoneal administration of P2A or FUS-iMSCs resulted in reduced tumor burden and extended survival. Immunohistochemical and flow cytometric analyses revealed massive infiltration of activated T cells, macrophages, and other immune cells into the tumor microenvironment (TME) in both FUS or P2A groups, but not in unmodified iMSC controls, or in PBS injected animals. The TME in P2A- and FUS-treated mice showed enrichment in tumoricidal M1-type macrophages, with no detection of exhausted or regulatory T cells, in contrast to controls.

Conclusions: IL7-IL15-secreting iMSCs migrate into solid tumors, induce massive immune cell infiltration into the TME and enhance antitumor immunity in a syngeneic mouse model of cancer. These cytokine-producing iMSCs represent a potentially promising anticancer immunotherapy by converting “cold” into “hot” tumor microenvironments.