Engineered IL7/IL15 secreting iPSC-derived mesenchymal stromal cells reprogram the immunosuppressive tumor microenvironment and potentiate antitumor immunity

Abstract Mesenchymal stromal cells (MSCs) derived from bone marrow (BM-MSCs) exhibit inherent tumor-tropic behavior, directed by chemotactic gradients involving CXCL12/CXCR4 and paracrine cues such as TGF-β, IL-6, and VEGF. Building on these properties, we previously engineered BM-MSCs to express interferon-β (IFN-β), eliciting robust antitumor immune responses in multiple preclinical tumor models and a phase I clinical trial in ovarian cancer showing effective recruitment of MSC to the TME and localized cytokine secretion. Notably, BM-MSCs demonstrated excellent tolerability in both murine models and patients. However, the finite proliferative lifespan, donor-to-donor variability, and senescence-associated transcriptional drift of BM-MSCs present barriers to clinical scalability. To address these limitations, 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, prior to mesodermal lineage specification into MSCs (hereafter referred to as IL7-IL15-iMSCs). Flow cytometry and transcriptomic profiling confirmed expression of canonical MSC markers (CD73⁺CD90⁺CD105⁺) and absence of hematopoietic (CD45⁻CD34⁻) or endothelial lineage antigens. IL7-IL15-iMSCs demonstrated trilineage differentiation potential and retained functional competence to support hematopoietic stem/progenitor cells (HSPCs) in CFU assays and NSGS mouse (Okeleji et al, ASH 2025). Functionally, they induced potent T cell proliferation, as assessed by CFSE dilution and STAT5 phosphorylation, and sustained the long-term expansion of T cells in vitro. Co-culture with peripheral blood mononuclear cells (PBMCs) activated tumor cell phagocytosis, indicating broad immunostimulatory activity. To mitigate pulmonary first-pass entrapment associated with systemic MSC delivery, we optimized a fractionated low-dose intravenous (IV) administration regimen in the orthotopic 4T1 triple-negative breast cancer model. This approach preserved lung histoarchitecture, while promoting stromal cell engraftment. 6 weeks post IL7-IL15-iMSC administration via IV, tissue IHC staining showed robust iMSC localization to the TME, localized secretion of IL7 and IL15, resulting in the TME modulation and infiltration of immune cells including CD4 as well as CD8 T cells, NK cells and macrophages into the primary tumor mass is significantly enhanced and tumor size reduced as indicated by bioluminescence imaging as compared to no MSC and iMSC alone control groups. Conclusion 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. The scalability of iPSC-derived MSCs, combined with synthetic mRNA reprogramming and stable cytokine expression, renders this platform well-suited for clinical translation.