Cross-reactive staining of normal bone-marrow cells by monoclonal antibody 2E11

Abstract

The monoclonal antibody (MAb) 2E11 is commonly used for detection of microdisseminated epithelial cells in bone marrow of cancer patients. Surprisingly, in an earlier report 2E11 was shown to bind to mononuclear cells in bone marrow in 61% of healthy donors. In the present study we tested whether this cross-reaction with non-epithelial bone-marrow cells can be characterized further. In addition, we analyzed the influence of 2E11 concentration on the staining of mononuclear cells. We performed immunocytochemical double stainings of bone-marrow aspirations from breast-cancer patients using 2E11/A45-B/B3 (MAb against cytokeratin 8, 18, 19) and 2E11/CD45 (MAb against CD45-leukocyte common antigen), while tumor cell lines MCF-7 and K526 as well as bone marrow from breast-cancer patients were treated with different concentrations of 2E11. A portion of 2E11-positive cells was characterized as hematopoietic cells by CD-45-binding, while others were identified as epithelial cells by A45-B/B3-binding. We defined a concentration of 2E11 to immunolabel epithelial cells and distinguish hematopoietic cells. Higher concentrations of 2E11 enhance staining of hematopoietic cells, to match that of epithelial cells. We conclude that 2E11 shows cross-reactivity to epitopes displayed by hematopoietic cells. However, specific staining of epithelial cells can be achieved. As long as there is no antibody available which is highly specific for epithelial cells, detection of microdisseminated tumor cells in bone marrow by antigen-antibody reaction should be verified morphological criteria.