CD26/dipeptidylpeptidase IV-targeted therapy of acute lung rejection in rats

Background: CD26 is a T-cell co-stimulator, and interacts with adenosine deaminase, human immunodeficiency virus (HIV) Tat-1 protein and extracellular matrix. It possesses dipeptidylpeptidase 1V (DPP TV) catalytic activity, which is linked to its co-stimulatory efficacy. We investigated the effect of specific DPP IV systemic activity inhibition on acute pulmonary rejection. Methods: Rat single-lung transplantation (Tx) was performed (LBNF1/LEW donor/recipient) in two groups (n = 12). Group I (n = 6) received daily treatment with a Pro-Pro-diphenylphosphonate derivative (AB197), and Group II served as an untreated control. At Day 5 post-Tx, ventilatory parameters, cytotoxicity and mixed lymphocyte reaction were analyzed and staining for ISHLT rejection grade and proliferating cell nuclear antigen (PCNA) was performed. Results: Treatment with AB192 abrogated acute rejection and preserved pulmonary function up to Day 5 post-Tx for PO2 (Group II: 24.9 +/- 6.9 mm Hg; Group I: 149.5 +/- 24.3 min Hg; p < 0.001), P-CO2 Group II: 53.3 +/- 13.6 mm Hg; Group L 39.0 +/- 9.8 min Hg; p < 0.05) and peak airway pressure (Group II: 50.7 +/- 17.2 mm Hg; Group 1: 20.2 +/- 10.0 min Hg; p < 0.01). Controls showed moderate/severe rejection (ISHLT Grade A2 or 3), grafts from inhibited hosts revealed no/mild rejection (Grade A0 to 2: Group 11: 2.8 +/- 0.3; Group 1: 1.25 +/- 1.0; P < 0.005). Proliferating cell nuclear antigen (PCNA) staining of rejection-associated cellular infiltrates showed a significant reduction in positivity in perivascular infiltrates (34 +/- 11.5%; p < 0.05) and bronchial surface epithelium (31.7 +/- 10.6%; p < 0.05) in Group I vs Group 11 (55.9 +/- 8.4% and 57.2 +/- 4.5%). Conclusions: Irreversible enzymatic inhibition of DPP IV has been shown to abrogate acute pulmonary rejection, maintain pulmonary function, and preserve histomorphologic architecture. These results extend earlier findings and illustrate the role of CD26/DPP IV in alloantigen-mediated immune responses.