Abnormalities of myeloid progenitor cells after "successful" bone marrow transplantation

We studied recovery of peripheral blood- and bone marrow-derived myeloid progenitor cells (CFU-G,M) in 29 patients who received bone marrow transplants 2 mo to 8.5 yr previously. All patients had normal levels of peripheral blood neutrophils, normal bone marrow cellularity, and a normal myeloid-erythroid ratio. Both peripheral blood- and bone marrow-derived CFU-G,M were markedly reduced compared with normal controls and bone marrow donors [5 +/- 1/10(6) vs. 37 +/- 4/10(6) (P less than 0.001) and 23 +/- 5/2 x 10(5) vs. 170 +/- 21/2 x 10(5) (P less than 0.001)]. Five patients had no detectable CFU-G,M even when 10(6) bone marrow cels were plated. These abnormalities of CFU-G,M were unrelated to age, sex, diagnosis, conditioning regimen, dose of bone marrow cells transplanted, and presence or absence of graft-vs.-host disease. Patients who received either autotransplants or transplants from identical twins also had decreased or absent CFU-G,M indicating that allogeneic factors and posttransplant immune suppressor with methotrexate or corticosteroids were not major determinants of this abnormality. Co-culture of normal or donor peripheral blood or bone marrow mononuclear cells with recipients peripheral blood or bone marrow mononuclear cells, purified T cells, or serum failed to show any evidence of active CFU-G,M suppression. Furthermore, the abnormality of CFU-G,M could not be corrected by the addition of normal syngeneic (donor) hematopoietic cells or serum. Depletion of T-cells from recipient bone marrow by physical techniques resulted in marked increase in CFU-G,M (36 +/- 13 vs. 138 +/- 36; P less than 0.05). The abnormality could be reproduced in vitro by readdition of autologous T cells. In contrast to results with T cell depletion by physical techniques, T cell depletion with a monoclonal anti-T antibody (B7) and complement had no effect. These data indicate that most-transplant recipients have a marked abnormality in CFU-G,M when these cells are cultured in vitro. In at least some of these patients, the decreased cloning efficiency of CFU-G,M appears to be mediated by a suppressive effect of autologous T cells.