Expression of novel surface antigens on early hematopoietic cells

The purpose of this report is to demonstrate the expression of very recently identified surface antigens on CD34(+) and AC133(+) bone marrow (BM) cells. Coexpression analysis of AC133 and defined antigens on CD34(+) BM cells revealed that the majority of the CD164(+), CD135(+), CD117(+), CD38(low), CD33(+), and CD71(low) cells resides in the AC133(+) population. In contrast, most of the CD10(+) and CD19(+) B cell progenitors and a fraction of the CD71(high) population are AC133(-), indicating that CD34(+)AC133(+) cells are enriched in primitive and myeloid progenitor cells, whereas CD34(+)AC133(-) cells mainly consist of B cell and late erythroid progenitors, This corresponds to the highly reduced percentage of CD10(+) B cells and the absence of CD71(high) erythroid progenitors on AC133(+) selected BM cells, A portion of 0.2-0.7% of the AC133(+) selected cells do not coexpress CD34, These cells are very small and define a uniform CD71(-), CD117(-), CD10(-), CD38(low), CD135(+), HLA-DRhigh, CD45(+) population with unknown delineation, Four color analysis on CD34(+)CD38(-) BM cells revealed that virtually all of these primitive cells express AC133, Using an improved liposome-enhanced labeling technique for the staining of weakly expressed antigens, subsets of this population could be identified which express the angiopoietin receptors TIE (67.6%) and TEK (36.8%), the vascular endothelial growth factor receptors FLT1 (7%), FLT4 (3.2%), and KDR (10.4%), or the receptor tyrosine kinases HER-2 (15.4%) and FLT3 (CD135; 77.6%), Our results suggest that the CD34(+)CD38(-) population is heterogeneous with respect to the expression of the analyzed receptor tyrosine kinases.