Phenotypically and functionally distinct CD8(+) lymphocyte populations in long-term drug-free tolerance and chronic rejection in human kidney graft recipients

A substantial proportion of long-term kidney graft recipients, including those with a stable renal function in the absence of immunosuppressive therapy, present a skewed T cell receptor (TCR) V beta chain usage, essentially in the CD8(+) subset. This study analyzed in more detail phenotypical and functional alterations of CD8(+) lymphocytes in drug-free tolerant patients (DF-Tol) compared with recipients with chronic rejection (CR). Phenotyping revealed a significant increase in central memory and a decrease in effector CD8(+) lymphocytes in DF-Tol versus CR. The expression of CD28(+) and CD27(+) on these effector cells was significantly decreased in CR. These profiles were stable over time and independent of treatment. Functionally, the CD8(+)CD28(-) lymphocytes were less sensitive to apoptosis than their CD8(+)CD28(+) counterparts, without differences in polyclonal proliferation. The CD8(+)CD28(-) cells did not express GITR and FoxP3 but were characterized by high levels of preformed perforin and granzyme A, pointing toward a cytotoxic rather than a suppressor function. CD8+CD28- lymphocytes did not show antigen-specific degranulation when co-cultured with targets that bear donor HLA class I antigens, suggesting that the cytotoxicity is directed either to other determinants of the graft or to nongraft epitopes. Of interest, CD8(+) cells from DF-Tol displayed the same profile as healthy individuals, indicating an increase in CD8(+)CD28(-) effector lymphocytes in CR rather than a decrease in DF-Tol. CD8(+) lymphocytes from stable kidney recipients under conventional maintenance immunosuppression displayed a mixed profile, independent of treatment and time of sampling. Taken collectively, these data show a strong cytotoxicity-associated CD8(+)CD28(-) signature in CR and suggest a suppression of pathologic cytotoxicity in DF-Tol. Further prospective studies should assess whether serial CD8(+) phenotyping may help to identify patients who are at risk for CR when immunosuppression is tapered.