Pattern of bone marrow regeneration following chemotherapy for acute myeloid leukemia.

Hematopoietic regeneration following chemotherapy was studied in serial bone marrow biopsy (BMB) specimens from 20 patients with acute myeloid leukemia (AML) who went into complete remission following therapy. Immediately after intensive chemotherapy, the marrow was extremely hypocellular and edematous and contained widely dilated sinuses. Subsequently, areas of large uniform unilocular fat cells developed from multilocular precursor fat cells. Early aggregates of regenerating hemopoietic cells were seen closely adjacent to bony trabeculae (BT) and appeared to grow out from the endosteum in a sequential progression suggesting an origin from their endosteal progenitors. During the early part of hemopoietic regeneration, individual precursor cells appeared to migrate from these hemopoietic aggregates towards the central intertrabecular marrow space where they formed colonies of various hematopoietic cells in close association with fat and marrow sinusoids. Later, as the normal hemopoiesis was restored due to the gradual enlargement and confluence of these hemopoietic colonies, this characteristic pattern of paratrabecular proliferation and migration of cells became less obvious. These observations suggest that hemopoietic regeneration in AML after therapy is a local phenomenon and is initiated by progenitors of endosteal cells.