Received February 16, 2005
Accepted on October 17, 2005

CLINICAL SCIENCE: Clinical Transplantation

Phenotypically and Functionally Distinct CD8⁺ Lymphocyte Populations in Long-Term Drug-Free Tolerance and Chronic Rejection in Human Kidney Graft Recipients

Dominique Baeten ^*, Stéphanie Louis ^*, Christophe Braud ^*, Cécile Braudeau ^*, Caroline Ballet ^*, Frédéric Moizant ^*, Annaik Pallier ^*, Magali Giral ^*, Sophie Brouard ^*, and Jean-Paul Soulillou ^*1

*Institut National de la Santé Et de la Recherche Médicale (INSERM), Unité 643: "Immunointervention dans les Allo- et Xénotransplantations," and Institut de Transplantation Et de Recherche en Transplantation (ITERT), Nantes, France; and Department of Clinical Immunology and Rheumatology, Amsterdam Medical Center, Amsterdam, The Netherlands

¹ To whom correspondence should be addressed. E-mail: jean-paul.soulillou{at}univ-nantes.fr.

	Abstract

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 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.