DPP4-inhibition reduces pro-inflammatory cytokine production by alpha-beta and gamma-delta T cells in vitro and in the biliary atresia mouse model

Etiology and pathogenesis of biliary atresia (BA) remain elusive. Evidence points to a T cell mediated autoimmune response contributing to the disease by driving the ongoing hepatic inflammation. CD26, also known as dipeptidylpeptidase 4 (DPP4), is an immunoregulatory protein also expressed on T-lymphocytes. We aimed to investigate the potential of pharmacological DPP4 inhibition on cytokine production of T cells and potential therapeutic benefits in experimental BA. We analyzed the expression and regulation of CD26/DPP4 on αβ and γδ T cells in mice suffering from rotavirus-induced BA. Enzymatic DPP4 activity in murine and human serum was examined. In cell cultures, lymphocytes were incubated with the DPP4-inhibitor Sitagliptin to study the effects of DPP4 inhibition on cytokine production. Clinical effects were assessed by intraperitoneal Sitagliptin injection of mice suffering from BA. Analyses included flow cytometry, qPCR, serum analysis and histological examinations. In mice suffering from BA, CD26/DPP4 was strongly expressed and upregulated on αβ and to an even greater extent on γδ T cells compared to healthy controls. DPP4-inhibition led to a dose-dependent suppression of the pro-inflammatory cytokines IL-17 and IFN-γ produced by Th1, Th17 and γδ T cells. Therapeutic administration of Sitagliptin in experimental BA led to reduced serum levels of GOT and Bilirubin as well as decreased hepatic infiltration with F4/80⁺ macrophages but had no effect on overall survival. In humans, serum DPP4-activity was upregulated in infants suffering from BA compared to healthy children. To our knowledge, this is the first time an upregulation of CD26 expression has been demonstrated for γδ T cells in the setting of an autoimmune inflammatory response. Mechanistically, we could demonstrate that DPP4/CD26 is upregulated on T cells in experimental BA and that pharmacological inhibition decreased their pro-inflammatory potential. However, this translated to only mild clinical benefits in the mouse model. Thus, although the protein appears to play a role in BA, further research is needed to elucidate the potential to serve as a therapeutic target.