Histological characterization of bone marrow in ectopic bone, induced by devitalized Saos-2 human osteosarcoma cells.

Devitalized Saos-2, cultured human osteosarcoma cells, or guanidinium-hydrochloride (GuHCl) extracts of these cells, induce ectopic bone and marrow formation when implanted subcutaneously in Nu/Nu mice. The aim of the present study was to characterize the bone marrow induced by Saos-2 cell extracts, specifically to determine which of the four major hematopoietic cell lineages: erythropoietic, granulopoietic, lymphopoietic and megakaryocytic, are induced by Saos-2 cell derivatives. Methods: Immunohistochemical localization of specific antigens was used to determine the presence of each major cell type (glycophorin A for erythropoietic, neutrophil elastase for granulopoietic, factor-VIII related antigen for megakaryocytes, and CD79a for B lymphocytes). Results: Standard H & E stains confirmed the presence of normally organized apparently complete bone marrow within all newly induced bone at 3 weeks post-implantation of devitalized Saos-2 cells. Immunohistochemistry confirmed the presence of erythropoietic cells, granulopoietic cells, megakaryocytes and B lymphocytes in the ectopic marrow. Conclusion: Saos-2 cells (freeze-dried) or their extracts, implanted subcutaneously into Nu/Nu mice, can induce normal marrow that is host-derived, and contains all major hematopoietic cell lineages. Clinical Significance: Saos-2 induced marrow could potentially restore deficient marrow and promote bone repair.