Increased expression of the lymphocyte early activation marker CD69 in peripheral blood correlates with histologic evidence of cardiac allograft rejection

Background The human leukocyte membrane protein CD69 is an early activation marker induced in T lymphocytes, B cells, and natural killer cells in response to inflammatory stimuli. Cardiac catheterization and endomyocardial biopsy remain the "gold standard" for diagnosis of rejection after transplantation, and noninvasive methods of rejection surveillance have long been sought. We studied CD69 membrane protein expression in peripheral blood T lymphocytes obtained from pediatric cardiac transplant recipients at the time of biopsy and correlated the results with histologic rejection scores. Methods. Heparinized whole blood samples were obtained from pediatric cardiac transplant recipients at the time of cardiac biopsy, as well as from control subjects. Lymphocytes were labeled with antibodies for CD3, CD4, CD8, and CD69 and analysis performed using flow cytometric methods. Results. Resting CD69 expression (measured as a percentage of gated events) was significantly increased in patients with concurrent histologic evidence of rejection (International Society for Heart and Lung Transplantation grade greater than or equal to 3A) when compared to those with minimal or no rejection and controls. Although statistically significant for both lymphocyte subsets, this relationship was more pronounced for CD8+ T cells (P<0.001) than for CD4+ T cells (P=0.001). When data were analyzed by rejection score, a percentage activation of the CD8+ subset (CD69+/CD8+ cells as a percentage of total gated events) exceeding 15% correlated with significant rejection. Conclusions. Measurement of the expression of the early activation marker CD69 in peripheral blood lymphocytes by flow cytometry may provide a noninvasive means of assessing immune activation and possible rejection in cardiac transplant recipients.