IL17A and chronic graft versus host disease: The PSGL1hi Th1, Th2, and Th17 cross-reactive autoreactive Trm cells interact with DCs and macrophages to mediate chronic GVHD pathogenesis via their production of cytokines such as TGF-β, IFN-γ, TNF-α, IL-4, IL-17, and IL-22.