Abstract
CD33, a 67-kDa sialoglycoprotein expressed on the cell surface of monocytic/myeloid lineage and early hematopoietic progenitor cells, is frequently expressed in patients with acute myeloid leukemia (AML). Gemtuzumab ozogamicin (GO), an immunoconjugate consisting of a humanized anti-CD33 antibody and a cytotoxic compound (N-acetyl-γ-calicheamicin dimethylhydrazine), targets CD33 and has shown promising results in patients with AML. No evidence of a relationship between the levels of CD33-positive leukemic cells and clinical response has been found. We investigated the possibility that cell-free circulating CD33 (cCD33) might be useful as a marker of clinical behavior. We used a newly developed bead-based immunoassay to measure cCD33 in the plasma of patients with AML (n = 97) or myelodysplastic syndrome (MDS; n = 44). All patients were treated with standard therapy including idarubicin and ara-C. cCD33 levels were significantly higher in patients with MDS (median, 1600 U/μL; range, 102–791,350 U/μL) than in those with AML (median, 2709 U/μL; range: 62–263,349 U/μL) (P = 0.004). High-risk cytogenetic abnormalities were associated with higher cCD33 levels in patients with MDS (P = 0.04) but not in patients with AML (P = 0.72). cCD33 levels correlated with WBC count and % monocytes in patients with AML (R >0.35) but not in patients with MDS. cCD33 levels correlated with clinical behavior only among AML patients with intermediate-risk cytogenetic abnormalities (n = 56); those with cCD33 levels above the median had longer survival (P = 0.04). These data confirm the presence of cCD33 in AML and MDS and also suggest that cCD33 can be used as a tumor marker in patients with AML. Although further study is needed for confirmation, cCD33 appears to result from turnover of leukemic cells, may play a role in patients being treated with GO, and should be considered in the pharmacokinetic and pharmacodynamic studies of such therapy.
cCD33 in AML patient with intermediate cytogenetic abnormalities
Disclosure: No relevant conflicts of interest to declare.
