The control of anti-donor immune responses by regulatory T cells in organ transplant patients

The role of regulatory T cells in the induction and maintenance of transplant tolerance has been widely investigated in experimental animal models. Their involvement in the regulation of allogeneic immune reactivity in immunosuppressed organ transplant patients, however, remains unclear. Measurements of regulatory T cells after clinical organ transplantation may contribute to understanding their role in anti-donor immune responses. Several studies have investigated the frequency and/or immune regulatory function of peripheral regulatory T-cell populations, such as, the CD4(+)CD25(+) regulatory T cells or the CD8(+)CD28(-) suppressor T cells, in clinically stable organ transplant patients and patients with acute or chronic rejection. This review summarizes these studies and discusses the correlations found between the number and function of regulatory T cells and the immunological state of the patient. This knowledge is warranted for a better understanding of the control of allogeneic immune responses by regulatory T cells. Subsequently, monitoring regulatory T cells may help us to identify patients in whom the anti-donor reactivity is actively suppressed