Expression of Novel Surface Antigens on Early Hematopoietic Cellsa

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Abstract
Abstract: 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+, CD38low, CD33+, and CD71+ cells resides in the AC133+ population. In contrast, most of the CD10+ and CD19+ B cell progenitors and a fraction of the CD71high 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 CD71high 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−, CD38low, 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.