CD34⁺ cell-derived endothelial cells orchestrate vascular and immune remodeling in the transplanted liver

Endothelial cell (EC) damage is an initiating event in acute cellular rejection after liver transplantation (LT). However, the origin and characteristics of post-transplant neonatal ECs remain controversial. We aimed to uncover the mechanisms underlying EC-T cell interactions after transplantation and to develop an EC-targeted strategy to alleviate transplant rejection.

Leveraging single-cell RNA sequencing from 13 human and 4 murine liver allografts, we mapped the functional atlas of ECs. Allogeneic orthotopic LT in CAG;R26-tdTomato and Cd34-CreER^T2;R26-tdTomato mice confirmed the cellular origin of ECs. We used CellChat, multiplex immunohistochemistry, and in vitro co-culture models to investigate the mechanism of EC-T cell interactions. Using a platelet-based bio-delivery system, we achieved targeted delivery of a CXCL12 monoclonal antibody (αCXCL12).

ECs in transplanted livers exhibited a dual origin, being derived from both donor and recipient cells. Recipient-derived ECs were characterized by high CD34 expression, high stemness, and pro-inflammatory characteristics. Using genetic lineage-tracing mice combined with an orthotopic LT model, we found that recipient CD34⁺ cell-derived ECs peaked at 2 weeks post-LT and declined by 4 weeks, consistent with the temporal pattern of rejection. We further identified that CD34⁺ ECs recruit and potentiate Th1 and cytotoxic CD8⁺ T cells via the CXCL12-CXCR4 axis and co-stimulatory molecules. In turn, cytotoxic CD8⁺ T cells induced pyroptosis of CD34⁺ cell-derived ECs through the Caspase1-GSDMD pathway. Platelets loaded with αCXCL12 specifically targeted ECs in the transplanted liver, reducing T-cell infiltration and mitigating rejection.

We identified a population of recipient-derived CD34⁺ ECs that exacerbates acute rejection by activating T cells through the CXCL12-CXCR4 axis. We further developed a platelet-based delivery strategy that precisely targets EC-derived CXCL12 and effectively prevents acute cellular rejection.

We integrated single-cell transcriptomic data from human and murine liver allografts to delineate the dual cellular origins and functional atlas of endothelial cells. Using lineage-tracing mice in an allogeneic orthotopic liver transplantation model, we tracked the fate of CD34⁺ cells and demonstrated the contribution of recipient-derived CD34-lineage endothelial cells to liver allograft angiogenesis. These CD34-lineage endothelial cells recruited T cells through the CXCL12-CXCR4 axis and activated them via co-stimulatory molecules. Furthermore, a platelet-based biological delivery strategy targeting CXCL12 in CD34-lineage endothelial cells alleviated T cell-mediated rejection. This study provides an endothelial cell-centered perspective and proposes a potential novel immunosuppressive strategy for liver transplantation.