Donor T-Derived Memory Progenitors Differentiated into CD103+/- CXCR6+CD4+ Tissue-Resident T Cell Subsets Driven Cutaneous Chronic Graft-Versus-Host Disease

Cutaneous chronic graft versus host disease (cGVHD) is the major clinical manifestation of cGVHD patients. Tissue-resident memory T (Trm) cells and TCF1⁺ T progenitors locally in GVHD target tissues play important roles in maintaining GVHD. However, the mechanisms regulating TCF1⁺ progenitor differentiation into Trm in the skin remain largely unknown. In the current studies, with cGVHD murine models (C57BL/6 donors and BABL/c recipients) and humanized models of human HLA-A2^-DR4^- PBMC to MHC^-/-HLA-A2⁺DR4⁺ NSG mice, we observed with flow cytometry analysis that most (>90%) of the injected donor CD4⁺ T cells in the skin tissues were CD69⁺ Trm, and the TCF1⁺ progenitors were less than 4%, which was markedly lower than in the liver and lung (>20%). The majority of Trm cells in the cGVHD skin were CD103⁺CXCR6⁺Foxp3^- conventional CD4⁺ T cells that produce large amount of pro-inflammatory IFN-γ and GM-CSF, while CD103⁺ Trm cells in the skin of non-GVHD recipients were mostly Foxp3⁺ Treg cells. Genetic deficiency of T-bet, BHLHE40, STAT3 or BATF in the injected donor T cells markedly ameliorated skin cGVHD, all associated with lower numbers of CD103⁺ Trm cells and lower production of IFN-g/GM-CSF. Results were similar when skin cGVHD was greatly reduced by post-transplantation treatment with cyclophosphamide (PTCY) in murine models. In addition, scRNA-seq analysis of blood and skin T cells from GVHD patients in a public dataset showed that ~90% blood T cells express stemness related marker Tcf7 and large proportions of skin T cells (>95%) express terminally differentiated markers such as Cxcr6. Taken together, our results suggest that the differentiation of TCF1⁺ T progenitor cells into Trm cells in the skin is regulated by the T-bet/BHLHE40 axis and the TCR/STAT3/BATF axis. Although Trm cells are differentiated from TCF1⁺ T progenitor cells in the skin, the TCF1⁺ T progenitor cells in blood may play an important role in replenishing TCF1⁺ T progenitor cells in cGVHD target tissues.