Gradients of antigen expression and developmental potential in hematopoiesis

Prospective isolation of hematopoietic stem and progenitor cell subsets depends upon the premise that expression of combinations of surface antigens reflects developmental potential. During the process of differentiation, however, the loss of antigens associated with stem cells and the concomitant gain of those associated with progenitor cells often occurs as a continuum rather than by discrete binary steps. Coupled with the fact that assay conditions can profoundly influence the developmental fates of prospectively isolated cells, gradients of antigen expression during differentiation have led to a variety of interpretations of lineage commitment in hematopoiesis.