Myeloid Cell-Targeting PLGA Nanoparticles Ameliorate Acute Graft-Versus-Host Disease

Background: Graft-versus-host disease (GVHD) is a common severe complication of allogeneic hematopoietic stem cell transplant. The current treatments are limited by steroid toxicity, broad immunosuppression, and the potential suppression of the graft-versus-tumor (GVT) effect. Developing less toxic therapies is an unmet need. We previously showed that systemically infused negatively charged immune-modifying microparticles (IMPs) composed of carboxylated poly-lactic-co-glycolic acid are taken up by inflammatory monocytes via the MARCO receptor, reducing symptoms and improving survival in inflammatory conditions. We hypothesized that IMPs could reduce acute GVHD manifestations. Methods: Acute GVHD was induced in an MHC-mismatched murine transplant model with radiation conditioning. IMPs were infused for five days; outcomes were compared to saline controls. We assessed organ histopathology, immune cell populations in the spleen and intestine, serum cytokine levels, and the GVT effect. Results: IMP-treated mice showed significant improvements in terms of clinical GVHD scores, histopathology, and survival. They had increased regulatory T-cells in the spleen and intestine and decreased colonic inflammatory monocytes and cytokines such as IL-6 and IFN-γ. IMPs were ineffective in MARCO knockout mice, confirming receptor dependence. Importantly, GVT activity was preserved, as evidenced by improved survival in mice with A20 lymphoma treated with IMPs. Conclusions: Systemic IMPs reduce clinical GVHD signs and improve survival, likely by decreasing inflammatory monocytes via MARCO and expanded regulatory T-cells numbers, while maintaining GVT activity. These findings support further investigation of IMPs as a targeted GVHD therapy.