Submitted January 7, 2008
Accepted May 1, 2008
Soluble CD22 as a tumor marker for hairy cell leukemia
Kakushi Matsushita, Inger Margulies, Masanori Onda, Satoshi Nagata, Maryalice Stetler-Stevenson, and Robert J Kreitman*
Laboratory of Molecular Biology, NCI, Bethesda, MD, United States
Laboratory of Pathology, NCI, Bethesda, MD, United States
* Corresponding author; email: kreitmar{at}mail.nih.gov.
CD22 is an important immunotherapeutic target on B-cell malignancies, particularly hairy cell leukemia (HCL), but its soluble extracellular domain, sCD22, has not yet been reported in the blood. By immunoaffinity and ELISA techniques using anti-CD22 monoclonal antibodies (MAbs), we identified the 100 kDa extracellular domain of CD22 and an 80 kDa processed form in serum of patients with HCL. The median sCD22 levels measured by ELISA was 18 ng/ml for 93 patients with HCL. sCD22 levels varied from 2.1-163 ng/ml and were higher (p < 0.0001) than 23 normal donors (median 0.6 ng/ml). Over 95% of normal donors had sCD22 levels < 1.9 ng/ml. sCD22 levels were proportional to concentrations of circulating HCL (p=0.0023) cells, and HCL spleen size (p<0.0001). sCD22 levels normalized with complete but not partial response to treatment. sCD22 levels up to 300 ng/ml had less than a 2-fold effect on the cytotoxicity of the anti-CD22 recombinant immunotoxin BL22. sCD22 levels may be useful to follow in patients with HCL, and may be more specific than sCD25 in patients with CD22+/CD25-negative disease. Trials listed on Cancer.gov: NCT00002765, NCT00021983, NCT00074048, NCT00085085, NCT00337311, NCT00462189.
