Pathophysiology and Treatment Opportunities of CX3CL1 in Liver Acute Gvhd

Acute graft-versus-host disease (aGVHD) is one of the most familiar and severe complications of hematopoietic stem cell transplantation (HSCT). Liver aGVHD, which has limited response to treatment and high mortality, is a critical concern among clinicians in the field. Chemokine (C-X3-C motif) ligand 1 (CX3CL1), also called fractalkine, as a chemokine and adhesion molecule, plays an important role in the pathogenesis of rheumatoid arthritis, primary biliary cirrhosis, and multiple sclerosis. Whether CX3CL1 is involved in liver aGVHD has not been investigated. We collected peripheral blood samples from 10 patients with liver aGVHD during the onset phase and 15 patients without aGVHD after HSCT. The results of the enzyme-linked immunosorbent assay (ELISA) indicated a significant increase in serum CX3CL1 levels among patients with liver aGVHD. Similarly, we observed elevated levels of CX3CL1 in the serum of a mouse model with aGVHD, and found a positive correlation between elevated bilirubin levels and higher serum CX3CL1 levels. The expression of CX3CL1 was markedly elevated in the liver of aGVHD mice by real-time quantitative polymerase chain reaction (RT-qPCR), western blotting (WB). The results of immunohistochemistry showed that the expression of CX3CL1 in the bile duct epitheliums of aGVHD mice was significantly increased compared with those of control mice, but not in hepatocytes. To further analyze CX3CL1 expression, we isolated hepatocytes and bile duct epitheliums from mice and measured the levels using RT-qPCR and WB. Similar to the results of immunohistochemistry, the expression level of CX3CL1 in bile duct epitheliums from aGVHD mice was increased significantly, while the expression level in hepatocytes was unchanged. The prominent bile duct damage observed in liver aGVHD may be attributed to the high CX3CL1 expression in bile duct epitheliums instead of hepatocytes. Anti-CX3CL1 monoclonal antibody (mAb) significantly improved the clinical symptoms and survival rates of liver aGVHD mice, and the liver enzymes and bilirubin levels were decreased remarkably after treatment. Additionally, HE staining showed that the application of anti-CX3CL1 mAb obviously reduced the infiltration of inflammatory cells in bile duct epithelium of liver aGVHD mice. In conclusion, these results provide evidence for the close relationship between CX3CL1 and the pathogenesis of liver aGVHD, suggesting anti-CX3CL1 mAb as a promising strategy for the management of liver aGVHD.

Keywords: Hematopoietic stem cell transplantation, Liver aGVHD, CX3CL1, Bile duct