Chimerism analysis of hematopoietic cells has emerged as an essential tool in nonmyeloablative hematopoietic stem cell transplantation. We have investigated the development of donor chimerism in granulocytes and CD4 ؉ and CD8 ؉ T cells in blood and bone marrow of 24 patients with hematologic malignancies who received HLA-identical sibling peripheral blood stem cell grafts after conditioning with fludarabine and 2 Gy of total body irradiation. The T-cell chimerism of blood and bone marrow was

more »

... htly correlated. Complete donor chimerism was reached earlier in the granulocytes than in the T cells. Mixed T-cell chimerism was common at the time of onset of acute graft-versus-host disease (aGVHD), and both CD4 ؉ and CD8 ؉ donor T-cell chimerism increased with the occurrence of aGVHD grades II to IV (P ‫؍‬ .0002 and P ‫؍‬ .019, respectively). The rate of disappearance of recipient CD8 ؉ T cells was faster in patients with aGVHD grades II to IV than in patients without clinically significant aGVHD (P ‫؍‬ .016). This observation indicates a role of graft-versuslymphohematopoietic tissue reactions in creating complete donor T-cell chimerism. A donor CD8 ؉ T-cell count above the median on day ؉14 increased the risk of subsequent development of aGVHD grades II to IV (P ‫؍‬ .003).