Multi-armored mesenchymal stem cells potentiate antitumor immunity to combat ovarian cancer

Ovarian cancer (OC) remains one of the most lethal gynecologic malignancies often resistant to immune checkpoint blockade (ICB) due to poor infiltration of cytotoxic CD8⁺ T cells and type 1 conventional dendritic cells (cDC1s) into the tumor microenvironment (TME). To overcome this, we engineered magnetic resonance imaging (MRI)-visible mesenchymal stem cells (MSCs) to co-express interleukin-15 (IL-15) for T-cell activation and XC motif chemokine ligand 1 (XCL1) for cDC1 recruitment, aiming to remodel the TME and enhance therapeutic outcomes.

MSCs were engineered via lentiviral transduction to stably express Il15, Xcl1, and a ferritin reporter for MRI tracking. In vitro validation included assays for gene expression, cytokine secretion, T-cell proliferation, and DC migration. Therapeutic efficacy was evaluated in subcutaneous (ID8) and disseminated (intraperitoneal FLUC-eGFP-ID8 and intra-omental FLUC-eGFP-OVHM) murine OC models. Mice received peritumoral (subcutaneous model) or intraperitoneal (disseminated models) injections of engineered MSCs (1×10⁷ cells). Anti-PD-1 antibody (10 mg/kg, twice weekly) was administered intraperitoneally in disseminated models. Tumor progression was monitored by MRI, bioluminescence imaging, and survival analysis. Immune cell infiltration and phenotypes were assessed using flow cytometry, qPCR, immunofluorescence, and immunohistochemistry.

Engineered MSCs sustainably secreted IL‑15 and XCL1, enhancing T cell proliferation and cDC1 migration in vitro. In vivo MRI confirmed efficient MSCs homing to subcutaneous tumors, suppressing tumor growth. In disseminated models, multi-armored MSC therapy inhibited tumor progression and prolonged survival, with combination therapy achieving superior outcomes. Mechanistically, this treatment drove a robust infiltration of CD8⁺ T cells and cDC1s into the TME. Flow cytometry revealed a beneficial shift in the CD8⁺ T-cell compartment toward progenitor-like, proliferative, and effector phenotypes. Furthermore, tumor-infiltrating cDC1s displayed elevated expression of co-stimulatory molecules CD80 and CD86, indicating enhanced activation.

MRI-visible MSCs co-expressing IL-15 and XCL1 effectively target ovarian tumors and remodel the immune microenvironment to foster potent anti-tumor immunity. By recruiting activated cDC1s and promoting durable, functional CD8⁺ T-cell responses, these multi-armored MSCs synergize with ICB to overcome therapeutic resistance. This cellular immunotherapy represents a promising strategy for ICB-resistant OC and warrants clinical translation.