ABSTRACT
BACKGROUND: CD22 is a glycoprotein expressed on the surface of normal mature B cells and in the cytoplasm of normal B cell precursors. Cytoplasmic CD22 (cCD22) has been proposed as a immunologic marker for the diagnosis of B-lineage acute lymphoblastic leukemia (ALL) while membrane CD22 (mCD22) has been used as the marker for chronic lymphocytic leukemia, B-lineage lymphoma, and hairly cell leukemia, and mCD22 has not been routinely used for the diagnosis and subgrouping of ALL. The purpose of this study was to examine the expression of mCD22 in B-lineage ALL and its clinical significance. METHODS: From 1992 to April, 1998, the leukemic cells of 64 patients newly diagnosed as B-lineage ALL by immunophenotyping were analyzed by the direct immunofluorescence method using monoclonal antibodies including mCD22. RESULTS: mCD22 was positive in 53% (34/64) of all patients, 50% (21/42) of children and 59% (13/22) of adults. According to the immunologic classification, mCD22 was positive in 44% (4/9) of group II, 53% (19/36) of group III, 69% (11/16) of group IV, but negative in 3 cases of group V and VI. The complete remission rate of the mCD22 negative group in group III was significantly higher than that of the mCD22 positive group (P=0.008). There were significant differences in survival rates between the mCD22 positive group and the mCD22 negative group in group II, III and IV (P=0.046) and the above observed significant difference was seen when group III was separately tested (P=0.014). CONCLUSIONS: Our study demonstrated that the expression of mCD22 may be a poor prognostic factor in B-lineage ALL and that mCD22 shall be clinically used as a prognostic marker especially in group III, which is most common among the subgroups of B-lineage ALL.