Discrete clusters of hematopoietic cells in the marrow cavity of man after bone marrow transplantation

Discrete aggregates of hematopoietic cells were observed in the bone marrows of patients with aplastic anemia or acute leukemia 14 days after marrow transplantation. The great majority of such colonies were of a single cell type, and less than 3% contained two or more cell types. Erythroid, myeloid, and undifferentiated hematopoietic colonies were approximately equal in frequency.