Differential LAG3 expression in intestinal tissue reveals a dual-pathology model of steroid-refractory acute graft-versus-host disease

Introduction Acute graft-versus-host disease (aGVHD) of the gastrointestinal tract remains a leading cause of non-relapse mortality following allogeneic hematopoietic cell transplantation, and steroid-refractory intestinal aGVHD carries a particularly poor prognosis. CD8 + T cells are critical effectors of intestinal tissue injury, yet the molecular mechanisms underlying their pathogenic role remain incompletely understood, especially in the steroid-refractory state. Methods This study aimed to identify key biomarker genes associated with CD8 + T cell-mediated intestinal aGVHD and to characterize their expression dynamics in the steroid-refractory state. Integrative bioinformatics analysis was performed using the Gene Expression Omnibus dataset GSE79083 (a CD8 + T cell-dependent murine aGVHD model), with a human dataset (GSE134662) for independent validation. Hub genes were prioritized through protein–protein interaction network analysis and random forest machine learning. A murine aGVHD model was established for validation via clinical score, qRT-PCR, histopathology, and immunofluorescence double staining. Results Lag3 was identified as the top-ranked gene with high diagnostic discrimination. In the murine model, Lag3 was markedly upregulated in intestinal tissue of the aGVHD group, and immunofluorescence confirmed CD8 + LAG3 + T cell infiltration of the intestinal mucosa. Notably, the steroid-refractory group exhibited more severe colonic histopathological injury. In this group, Lag3 expression was significantly lower than in the aGVHD group despite persistent CD8 + T cell infiltration. A similar expression pattern was observed in the human dataset. Conclusion The reduction of Lag3 despite persistent severe tissue injury suggests that glucocorticoid-resistant CD8 + T cells may have escaped checkpoint-mediated restraint. These findings suggest a dual-pathology framework for steroid-refractory intestinal aGVHD, involving both effector mechanisms independent of LAG3 and impaired epithelial repair. Whether targeting both processes in combination would be beneficial remains to be tested.