Circulating CD33 and its clinical value in acute leukemia

Objective: CD33 is a cell surface antigen for committed myelomonocytic lineage. We explored the potential of detecting CD33 as cell-free circulating protein in patients with leukemia. Materials and Methods: We developed a quantitative bead-based immunoflow cytometry assay to measure cell-free circulating CD33 (cCD33) levels in the plasma of patients with acute leukemia, and correlated these results with corresponding clinical behavior. We measured cCD33 levels in the plasma of 48 healthy subjects and in patients with acute myelogenous leukemia (n = 98), acute lymphoblastic leukemia (n = 46), myelodysplastic syndrome (MDS) (n = 50), and myeloproliferative disorder (n = 49). Results: Patients with acute myeloid leukemia and myeloproliferative disorders had significantly higher concentrations of cCD33 than the other patient groups and normal individuals (p = 0.0001), and among these groups, MDS patients displayed the lowest cCD33 levels (p = 0.02). Circulating CD33 values correlated positively with the CD33⁺ blast cell counts in these patients. While there was no correlation between cCD33 levels and survival in acute myelogenous leukemia and MDS, higher cCD33 plasma concentrations did correlate with shorter survival in acute lymphoblastic leukemia (p = 0.03), and with shorter complete remission duration in acute myelogenous leukemia (p = 0.04) and MDS (p = 0.03). Conclusion: Circulating CD33 can be detected in the plasma from patients with leukemias, and cCD33 levels may have clinical implication, e.g., predictive and prognostic value, in these patients.