Effect of chemotherapy for acute myelogenous leukemia on hematopoietic and fibroblast marrow progenitors

Since reduced marrow cellularity and prolonged pancytopenia following autologous bone marrow transplantation (ABMT) have been frequently observed in patients with acute myelogenous leukemia (AML) included in the AML10 GIMEMA/EORTC trial, the question was raised to what extent hematopoietic and microenvironmental progenitor cells were involved in these patients. Marrow hematopoietic progenitors were investigated by a short-term methylcellulose assay quantitating multipotent CFU-Mix, erythroid BFU-E and granulocyte-macrophage CFU-GM, as well as a long-term assay quantitating long-term culture-initiating cells (LTC-IC). The marrow microenvironment was studied by evaluating the incidence of fibro-blastoid progenitors (CFU-F) and the capacity of stromal layers to support allogeneic hematopoietic progenitors. As compared to normal controls (n = 57), AML patients (n = 26) showed a statistically significant reduction of the mean (± s.e.m.) number of CFU-Mix (5.3 ± 0.6 vs 0.8 ± 0.2, P ≤ 0.0001), BFU-E (68 ± 5 vs 20 ± 4, P ≤ 0.0001), CFU-GM (198 ± 11 vs 144 ± 15, P ≤ 0.008), and LTC-IC (302 ± 46 vs 50 ± 8, P ≤ 0.001). The mean (± s.e.m.) incidence of marrow CFU-F was not significantly reduced as compared to normal controls (48 ± 6 vs 52 ± 7, P ≤ 0.73). Seventeen AML stromal layers were tested for their capacity to support the growth of allogeneic hematopoietic progenitors. Seven samples failed to support any progenitor cell growth, seven had a significantly lower supportive activity as compared to normal stromal layers (13 ± 5 vs 249 ± 56, P ≤ 0.002), whereas three cultures could not be analyzed due to contamination. In conclusion, induction and consolidation regimens used in AML patients of the AML10 protocol induce a markedly defective in vitro growth of primitive hematopoietic progenitors and a severe functional defect of marrow stroma. The association of hematopoietic with microenvironmental damage might play a key role in the delayed hematopoietic regeneration observed following ABMT in patients of the AML10 trial.