CD26/DPP IV in Experimental and Clinical Organ Transplantation

The T-cell activation-Ag CD26 possesses dipeptidyl peptidase IV (DPP IV) enzymatic activity. Costimulatory efficacy and immunocompetence are associated with the enzymatic activity. Goals: In models of experimental cardiac allograft transplantation (HTx), we analyzed the role of CD26/DPP IV during organ rejection. Also, we investigated CD26 enzymatic and cellular expression in human recipients of kidney transplants (Tx). Material and Methods: Heterotopic HTx in rats, models of acute and accelerated rejection. Monitoring of DPP IV serum levels and humoral immunity. Propro-diphenyl phosphonate was employed to inhibit DPP IV activity during rejection. In a prospective study, surface expression of CD26, 3, 4, 8, 45, 122 and ADA on PBL and DPP IV serum activity were measured in kidney recipients for 24 months post-transplantation. Results: Acute rejection was associated with increased serum DPP IV activity (p<0.005). Specific inhibition abrogated acute (p<0.0001) and accelerated (p<0.01) rejection, impairing cytotoxicity and allospecific Ig-synthesis. Kidney recipients displayed a significant drop in CD26 expression on PBL for up to 18 months postoperatively (p<0.001). CD4, 8, 45, 122 and ADA expression kinetics were only briefly affected. DPP IV enzymic activity stayed depressed for at least 12 months (p<0.001). Conclusion: CD26/DPP IV is pivotal in T-cell mediated immune responses toward allo-Ag. In clinical transplantation, engraftment/immunosuppression are reflected by CD26 cellular and enzymatic expression posttransplantation and may serve as an indicator for immunomodulation.