Histopathology of bone marrow reconstitution after allogeneic bone marrow transplantation.

In order to study haematopoietic reconstitution in allogeneic bone marrow transplantation we investigated bone marrow histology in 61 biopsies of 37 patients, treated with HLA-compatible bone marrow grafts for leukaemia or severe aplastic anaemia. The biopsies were taken from the day of transplantation until 100 d after transplantation. Stromal changes, in particular oedema, fibrosis and granulomas, were found during the whole period of observation. These changes were more prominent in biopsies from leukaemia patients than from patients with aplastic anaemia. The cellularity in the biopsies increased until 28 d after bone marrow transplantation and was stable thereafter. Initially, only clusters of cells belonging to a single cell lineage were seen, suggesting that the first outgrowth of haematopoietic cells is by proliferation of committed precursor cells. Long-lasting abnormalities in localization of haematopoietic cells in the bone marrow space and of the myeloid: erythroid ratio were seen; dyserythropoiesis was common.