Achievement of early complete donor chimerism in CD25+-activated leukocytes is a strong predictor of the development of graft-versus-host-disease after stem cell transplantation.

Chimerism dynamics in bone marrow, peripheral blood (PB), and T lymphocytes (TL) has been associated with the development of various complications after allogeneic stem-cell transplantation (allo-SCT). In the present study, the usefulness of chimerism monitoring in CD25 + -activated leukocytes (AL), together with that in bone marrow, PB, and TL, for the anticipation of complications after allo-SCT, has been analyzed in 68 patients. In AL, we observed a slower dynamics toward complete chimerism (CC) than in PB ( p = 0.042), while no significant differences were found between TL and PB ( p = 0.12). Complete chimerism achievement in AL at day +30 has shown to be an independent risk factor for the development of grade II–IV acute graft-versus-host disease (aGvHD; hazard ratio [95% confidence interval]: 11.9 [1.5–91.7]; p = 0.017). Moreover, among patients achieving CC in TL and AL at different time-points after SCT ( n  = 17/68), the incidence of grade II–IV aGvHD was significantly higher in patients who achieved CC earlier in AL (5/5) than in those who achieved CC earlier in TL (1/11; p = 0.001). Therefore, achievement of early complete donor chimerism in CD25 + AL is a strong predictor for the development of aGvHD. Prospective analysis of chimerism in AL could improve the post-SCT management of immunosuppressive therapy in transplanted patients.