Certain anti-CD34 monoclonal antibodies induce homotypic adhesion of leukemic cell lines in a CD18-dependent and a CD18-independent way.

CD34 is a highly glycosylated type I membrane protein expressed by early hematopoietic progenitor cells as well as by endothelial cells and a subset of bone marrow stromal cells. CD34 is thought to play an important role during early hematopoiesis, although its function is unknown. We demonstrate that triggering of CD34 results in a rapid and vigorous homotypic adhesion in CD34+ cell lines, thereby providing evidence for a cell-cell adhesion function of CD34. The cellular adhesion event, induced by only two anti-CD34 mAb, (Immu-133 and QBend-10) was dependent on metabolic energy, an intact cytoskeleton and the presence of divalent cations. Analysis of antibody inhibition experiments indicated that the aggregation process partially involved the CD18 molecule.