MHC disparity hampers thymus-dependent T-cell recovery post-hematopoietic transplantation through dysregulation of TGF-β1 and LRP6 pathways.

Clinical studies have demonstrated that recipients of allogeneic hematopoietic cell transplantation (alloHCT), particularly those undergoing HLA-haploidentical alloHCT (haploHCT), exhibit significant immune deficiencies. However, the extent to which major histocompatibility complex (MHC) disparity independently contributes to the observed lymphocyte deficiency post-alloHCT remains unclear. While MHC matching is crucial for thymic selection of T lymphocytes, it has yet to be reported whether haploHCT alters recipient thymus homeostasis compared to MHC-matched HCT and which signaling pathways are implicated in this alteration. In this study, we established mouse models of MHC- matched and haploidentical HCT without any transplant-associated complications. Our findings indicated that MHC disparity significantly disrupted thymic architecture, suppressed thymus-specific gene expression, and resulted in impaired T-cell recovery and functionality following transplantation. Single-cell transcriptomic analysis revealed abnormally enhanced interactions involving TGFB1-TGFBR3 and LRP6-CKLF between thymic lymphocytes and epithelial cells in haploHCT recipients. Furthermore, agonists targeting the TGF-β1 and LRP6 pathways were found to compromise the functional characteristics of normal thymic T cells; conversely, appropriate inhibition of these pathways restored the differentiation and maturation phenotypes of thymic T cells derived from haploHCT recipients. Our study elucidates the independent role of MHC disparity in regulating thymus homeostasis and T-cell recovery while identifying the functional involvement of the TGF-β1 and LRP6 pathways in this context. These findings provide novel insights into the mechanisms underlying immune recovery as well as potential therapeutic strategies for modulating thymic functions following haploHCT.