Partial Chimerism After T-Cell-Depleted Allogeneic Bone Marrow Transplantation in Leukemic HLA-Matched Patients: A Cytogenetic Documentation

We evaluated serially by cytogenetics the blood and marrow chimerism of 38 leukemic recipients of HLA-matched bone marrow transplants (BMT) who were prepared by high doses of alkylating agents and fractionated total-body irradiation (2.2 Gy x 5). Donor or host mitoses were identifled by examination of sex chromosomes in 32 patients or by evaluation of the polymorphism of other chromosomes after specific banding in six patients. Twenty-four patients were recipients of untreated BMT. and 1 4 were recipients of T-cell-depleted BMT. In the 24 patients who received untreated BMT. all showed successful engraftment. and only three had a transient mixed chimera. In the 14 recipients of T-cell-depleted BMTs. four rejected their grafts. and seven had mixed chimeras; these mixed chimeras were more frequent in blood lymphocytes than in marrow cells and could be detected up to 26 months after BMT. This high frequency of partial chimerism after Tcell- depleted BMT by comparison with a control group suggests that the donor’s T cells play an important role in the eradication of host residual hematopoiesis after allogeneic BMT.