CD34-positive cells : biology and clinical relevance

Cellular expression of the CD34 antigen identifies a morphologically and immunologically heterogeneous cell population that is functionally characterized by the in vitro capability to generate clonal aggregates derived from early and late progenitors and the in vivo capacity to reconstitute the myelo-lymphopoietic system in a supralethally irradiated host. Immunohistoc hemical studies have demonstrated that the CD34 antigen is stage but not lineage specific. In fact, indepen den t ly of the differentiative lineage, it is expressed on lyby on to genetically early cells . For years a major obstacle to the morphological identification of putative hematopoietic stem cell has been the difficulty in separating them from their direct progeny. The use of CD34 and other suitable cell surface markers (i.e. CD33, CD38, HLA-DR antigens) in fluorescence-activated cell-sorting techniques or other cell separation methods has allowed considerable progress in this field. In conclusion, born as a ‘compassionate’ surrogate of bone marrow autografting, today C PAT is rapidly replacing ABMT. In fact, today it is the latter that should be considered a ‘compassionate need ’ procedure, useful in those few patients unable to mobilize a sufficient number of circulating progenitor cells.