In graft-versus-host disease (GVHD), a life-threatening complication of hematopoietic stem cell transplantation, MSC infusions reduce pro-inflammatory cytokines (e.g., IFN-γ, IL-17) and expand regulatory T cells (Tregs), as demonstrated in the Phase III REMODEL trial, where 60% of steroid-refractory GVHD patients achieved complete remission (Kebriaei et al., 2020). Here, IL17A is linked to graft versus host disease.