BACKGROUNDInvasive kidney biopsy is a priority diagnostic method for the acute rejection after renal transplantation for the past decades. However, no effective and noninvasive assay for predicting the severity of acute rejection is in wide use at present. This study was designed to investigate the predictive value of programmed death 1 (PD-1) mRNA for acute rejection after renal transplantation with real-time reverse transcriptase polymerase chain reaction (RT-PCR). A noninvasive diagnostic method has been expected to replace the traditional kidney biopsy for the diagnosis of acute rejection and prediction of the outcome after kidney transplantation.

METHODSThe whole blood samples from 19 subjects with acute rejection, 20 subjects with delayed graft function (DGF) and 21 subjects with stable recipients after kidney transplantation in a single kidney transplantation center between 2006 and 2009 were collected. The messenger RNA (mRNA) of PD-1 was analyzed with real-time RT-PCR. The associations of PD-1 mRNA levels with acute rejection and disease severity were investigated.

RESULTSThe log-transformed ratio of PD-1 mRNA to GAPDH mRNA was higher in peripheral blood mononuclear cell (PBMC) from the group with acute rejection (4.52 ± 1.1) than that from the group with DGF (1.12 ± 0.6) or the group with normal biopsy results (0.7 ± 0.4) (P < 0.01, by the Kruskal-Wallis test). PD-1 mRNA levels were correlated with serum creatinine levels measured at the time of biopsy in the acute rejection group (Spearman's correlation coefficient, r = 0.81, P = 0.03), but not in the group with DGF or the group with normal biopsy results. PD-1 mRNA levels identified subjects at risk for graft failure within six months after the incident episode of acute rejection.

CONCLUSIONSOur data suggest that PD-1 status may be a new predictor of acute rejection and the levels of PD-1 mRNA in whole blood cells may positively correlate with the severity of acute rejection after renal transplantation. Meanwhile, the data provide the rational for interfering into the PD-1/PD-L1 as a novel therapy against the acute rejection after renal transplantation in clinical settings.