Two
monoclonal antibodies (To15 and 4KB128) specific for the B cell-associated
CD22 antigen (135,000 mol wt) are described. On immunoenzymatic analysis of cryostat tissue sections, these
antibodies strongly label both mantle zone and germinal center B lymphoid cells in secondary lymphoid follicles (and also scattered extrafollicular lymphoid cells) but are unreactive with other cell types (with the exception of weak reactivity with some epithelioid histiocytes). These reactions differ from those of
monoclonal antibodies B1 and B2 (anti-CD20 and CD21) but are similar to those of the pan-B antibody B4 (anti-CD19). One of the anti-CD22
antibodies (To15) has been tested extensively by immunoenzymatic labeling on greater than 350 neoplastic lymphoid and hematological samples. The
CD22 antigen was found in tissue sections in most B cell-derived
neoplasms, the major exceptions being myeloma (all cases negative) and a small proportion of
high-grade lymphoma (6% of cases negative). In cell smears, the
antigen could be found on neoplastic cells in most B cell
lymphoproliferative disorders, including common
acute lymphoblastic leukemia (ALL) (90% positive) and
B cell chronic lymphocytic leukemia (CLL) (89% positive). We conclude that anti-CD22
antibodies are of value for identification of human B cell
lymphoproliferative disorders (especially when used in conjunction with anti-CD19
antibodies). Previous reports that the
CD22 antigen is absent from many B cell
neoplasms are probably due to its being expressed within the cytoplasm of immature B cells rather than on their surface.