Detection of cardiac allograft rejection and response to immunosuppressive therapy with peripheral blood gene expression

Background - Assessment of gene expression in peripheral blood may provide a noninvasive screening test for allograft rejection. We hypothesized that changes in peripheral blood expression profiles would correlate with biopsy-proven rejection and would resolve after treatment of rejection episodes. Methods and Results - We performed a case-control study nested within a cohort of 189 cardiac transplant patients who had blood samples obtained during endomyocardial biopsy (EMB). Using Affymetrix HU133A microarrays, we analyzed whole-blood expression profiles from 3 groups: ( 1) control samples with negative EMB ( n = 7); ( 2) samples obtained during rejection ( at least International Society for Heart and Lung Transplantation grade 3A; n = 7); and ( 3) samples obtained after rejection, after treatment and normalization of the EMB ( n = 7). We identified 91 transcripts differentially expressed in rejection compared with control ( false discovery rate <0.10). In postrejection samples, 98% of transcripts returned toward control levels, displaying an intermediate expression profile for patients with treated rejection ( P < 0.0001). Cluster analysis of the 40 transcripts with > 25% change in expression levels during rejection demonstrated good discrimination between control and rejection samples and verified the intermediate expression profile of postrejection samples. Quantitative real-time polymerase chain reaction confirmed significant differential expression for the predictive markers CFLAR and SOD2 (UniGene ID No. 355724 and No. 384944). Conclusions - These data demonstrate that peripheral blood expression profiles correlate with biopsy-proven allograft rejection. Intermediate expression profiles of treated rejection suggest persistent immune activation despite normalization of the EMB. If validated in larger studies, expression profiling may prove to be a more sensitive screening test for allograft rejection than EMB.