Expression of CD66a in multiple myeloma

CD66a is a member of the carcinoembryonic antigen family and has been suggested to function as an intercellular adhesion molecule and cell growth regulator. Expression of CD66a in myeloma cells was examined with mAb TS135 against CD66a transfectants of murine-transformed fibroblasts. The reactivity of mAb TS135 with CD66a, CD66c, and CD66e was revealed. CD66a in myeloma cells was considered to be detectable with this mAb, since CD66c and CD66e are not expressed in them. CD66a was detected in three myeloma cell lines and an IgM-producing B-cell line. In clinical bone marrow specimens, including 18 multiple myeloma, two primary macroglobulinemia, and a case of CLL-like chronic lymphoproliferation with monoclonal IgG production, CD66a and three conventional myeloma cell markers (PCA-1, CD38, and CD56) were examined by indirect immunofluorescence assay. The results showed that 18 out of 21 cases (86%) were CD66a+, and PCA-1 showed the highest correlation with CD66a among conventional markers. Primary macroglobulinemia and chronic lymphoproliferation were also CD66a+. Two-dimensional flow cytometry with mAbs TS135 and CD38 confirmed the reactivity of TS135 with myeloma cells in those bone marrow specimens. The findings suggest that CD66a is expressed in multiple myeloma with high frequency.