Bone marrow concentrated cell transplantation: rationale for its use in the treatment of human osteochondral lesions

Bone marrow is one of the best characterized stem cell microenvironments that contains Mesenchymal Stem Cells (MSCs), a rare population of non-hematopoietic stromal cells. MSCs have been indicated as a new option for regenerative medicine because of their ability to differentiate into various lineages such as bone, cartilage and adipose tissue. However, isolation procedures are crucial for the functional activity of the transplanted cells. The use of concentrated bone marrow cells (BMCs) enables a cell population surrounded by its microenvironment (niche) to be implanted while avoiding all the complications related to the in vitro culture. The cells of the niche are able to regulate stem cell behavior through direct physical contact and secreting paracrine factors. The aim of this study was to characterize BMCs in vitro to evaluate their ability to differentiate toward mature cells and try to understand whether there are differences in the chondrogenic and osteogenic potential of cells from patients of different ages. Mononuclear Cells (MNCs) isolated by Ficoll were used as control. Both cell populations were grown in monolayers and differentiated with specific factors and analyzed by histological and molecular biology assays to evaluate the expression of some specific extracellular matrix molecules. The present investigations revealed the ability of BMCs to act as isolated cells. They are able to form colonies and differentiate toward chondrogenic and osteogenic lineages, the latter pathway appearing to be influenced by donor age. The results obtained by this study support the use of BMCs in clinical practice for the repair of osteochondral damage, which might be particularly useful for the one-step procedure allowing cells to be directly implanted in operating room.