Ex vivo expansion and genetic marking of primitive human and baboon hematopoietic cells

The achievement of positive outcomes in many clinical protocols involving hematopoietic stem cells (HSCs) has been handicapped by the limited numbers of marrow repopulating cells available to actually bring about therapy. This insufficiency has been especially problematic in stem cell transplantation and gene therapy. A number of studies have been initiated to attempt expansion of HSCs, mainly by manipulation of key cytokines in cell suspension cultures. Unfortunately, these expansion methods usually lead to altered properties in the amplified cells, mainly by reducing their self-renewal and multilineage differentiative potentials. Here we discuss our ongoing work, utilizing a unique endothelial cell line that supports primitive hematopoiesis, to attempt to generate expansion of primate HSCs that retain their elementary properties. Genetic marking of early hematopoietic cells to facilitate tracking will be mentioned as will the development and employment of assay systems designed to evaluate the long-term functional attributes of the expanded cells.