Exhausted-like effector CD8 T cells mediate immune-stromal interactions at mucosal Chronic Graft-versus-Host Disease onset

Chronic graft-versus-host disease (cGVHD) frequently follows allogeneic hematopoietic stem cell transplantation and impacts the mucosa. This atlas study highlights the role of exhausted-like effector CD8 ⁺ T cells (T _EXEF ) in oral mucosal cGVHD pathogenesis. Biopsies from the oral mucosa were collected at oral cGVHD onset or at six months post-transplant and analyzed using single-cell RNA sequencing and other modalities. At cGVHD onset, in addition to changes in the myeloid compartment, two distinct populations of CD8 ⁺ T cells with a T _EXEF phenotype were prevalent: an inflammatory CD8T cell cluster (CD8T_4) expressing CCL4 , CD69 , and TNFSF9 , and an exhausted CD8T cell cluster (CD8T_5) characterized by the expression of CXCL13 , HIF1A , and HLA-DRA, both correlated with clinical disease severity. Pseudo-time analysis suggests a transition from the inflammatory pre-exhausted CD8T_4 cluster to the cytolytic, terminally exhausted CD8T_5 cluster. The CXCL9-CXCR3 interactions among CD8 ⁺ T cells, fibroblasts and myeloid cells are implicated in tissue damage. Onset of cGVHD despite frequent oral mucosal FOXP3⁺ regulatory CD4⁺T cells suggests potential impaired Treg function or CD8 ⁺ T cell dysfunction. These findings highlight T _EXEF cells as key contributors to oral cGVHD pathology and potential therapeutic targets for mitigating sustained tissue injury in cGVHD.