(A) Western blotting study using biotinylated MoAbs 2E9 and 1H6. Lane 1 in each panel is CD34-Ig and lane 2 in each panel is a control fusion protein (CTLA4-Ig) that has the same murine IgG2A sequence as CD34-Ig. 1H6 and 2E9 recognize CD34-Ig but not CTLA4-Ig, indicating specific binding of 2E9 and 1H6 to the extracellular domain of CD34 as expressed in the fusion construct. (B) Western blots of cell lines ML1 (CD34⁻), ML3, and 1390 (both CD34⁺) using 2E9 and RPαCD34. The band for CD34 (∼110 kD) is indicated by the arrow. The other bands present on these blots were also detected in control experiments using only the second-stage reagents.