Studies on the in vitro microenvironment in man

In a preliminary manner, the data presented here characterize some features of MSC and their progenitors. The progenitors, at least in chronic myelogenous leukemia, are derived from the neoplastic pluripotent stem cell that also differentiates along lymphoid and myeloid pathways. In addition, we have demonstrated that the precursor for MSC is lacking both the Ia and CALLA determinants. Several antigenic and functional characteristics of the mature stromal cell population have also been identified. Stromal cells express CALLA, synthesize types I, III, and IV collagen, and may express factor VIII associated antigen. It is of interest that fibroblasts do not express factor VIII associated antigen, do not synthesize type IV collagen in measurable quantities, but do express CALLA [9]. Endothelial cells express factor VIII associated antigen, synthesize type IV collagen, but are not CALLA positive. Thus, MSC have some features in common with fibroblasts and others with endothelial cells. The unique characteristics of MSC are that they are transplantable and are derived from a common progenitor with other hematopoietic cells. These features clearly distinguish this cell population from fibroblasts, which are neither transplantable nor derived from the neoplastic clone in CML.