Tissue-Resident Double Negative T Cells Mediate Salivary Gland Damage in Chronic Oral Graft-Versus-Host Disease

Chronic graft-versus-host disease (cGVHD) is the most significant long-term complication of allogeneic hematopoietic stem cell transplantation (allo-HSCT). The oral cavity is frequently affected, second only to the skin, with the majority of cGVHD patients complaining of xerostomia. This condition significantly diminishes patients' quality of life. The manifestations of salivary gland damage in oral cGVHD are similar to classic Sjögren Syndrome, though its pathogenesis remains poorly understood.

Our study examined the pathological features within the salivary glands of cGVHD individuals, identifying periductal infiltration, gland atrophy, and fibrosis. In three murine cGVHD models, categorized as major MHC mismatched, haplo-HSCT and miHA-mismatched GVHD models, immune cell infiltration was mainly comprised of CD8+ T cells and double-negative T cells (DNTs). Notably, these DNTs expressed various cytotoxic molecules (e.g., KLRG1, Granzyme B) and inflammatory cytokines. Furthermore, higher levels of GITR, CXCR6, PD-1, and TIM-3 were observed in DNTs compared to CD8+ T cells, suggesting a TEM/TEMRA-like phenotype with pathogenic roles in cGVHD lesion formation. The DNTs in the major MHC mismatched model exhibited Th1/Tc1 signatures with increased IFN-γ and T-bet expression, while those in the haplo-HSCT model showed Th17/Tc17 signatures with higher IL-17 expression.

We found that the development of DNTs in the salivary gland is thymus independent. Lineage tracing, single-cell RNA, and TCR-CDR3 sequencing in mice showed that GITR+ DNTs originated from Tcf-1+CD8+ T cell progenitors. Moreover, the attraction of these cytotoxic DNTs by GITR ligand (GITRL) expressed on salivary epithelial cells led to glandular damage. Triggering mGITR with anti-mGITR antibodies (DTA-1) promoted the proliferation of DNTs in a CD8+ T cell-dependent GVHD model (C3HSW to B6/SJL)

Our findings reveal that the interplay between salivary epithelial cells and donor-derived DNTs is central to the pathogenesis of salivary gland damage in oral cGVHD. Moreover, these data indicate that the mechanism of salivary gland damage in oral cGVHD differs from that of oral mucosal cGVHD, which is driven by cytotoxic CD8+ T cells.

In conclusion, targeting the GITR/GITRL signaling pathways emerges as a potential therapeutic strategy for addressing salivary gland dysfunction in oral cGVHD. This finding opens new avenues for more specific and effective treatments for patients suffering from this debilitating condition.