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

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.

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.

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.

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.