Simultaneous Coexpression Measuring for Pretherapeutic Identification of Double-Positive CD33/CD64 AML, Immunophenotyping and Clinical Correlations: An Introduction for Direct Effect of Bispecific Anti-CD33 X Anti-CD64 Treatment on Proliferation and Signaling in Myeloid Cells

Background and objectives: Leukemia cells from patients with acute myeloid leukemia (AML) commonly express certain myeloid-specific antigens such as CD33 and CD64. Considerable efforts and attention have focused on targeting these antigens with monoclonal antibodies (mAb) for therapeutic effects and an understanding of the activity of the anti-CD33 X anti-CD64 bispecific antibody (BsAb) on myeloid cells has potential clinical significance. Design and methods: Hundred patients with primary AML (70 de novo AML and 30 relapsed AML), diagnosed according to FAB criteria and immunological marker studies, were examined for the dual expression on their blast cells of the CD33/CD64 immunophenotype coexpression by direct immunofluorescence assay using dual staining combination flow cytometry. The immunophenotype of AML was determined by flow cytometry. CD2, CD3, CD5, CD7, CD10, CDllb, CDl lc, CD13, CD 14, CD15, CD19, CD20, CD33, CD34, HLA-DR, TdT expression were analyzed. Results: In 89/100 AML patients analyzed (89%), blast cells coexpressed the CD33 and CD64 antigens. Moreover, in 52 of them, i.e., 52/89 (58% of the 89 positive CD33/CD64 cases) (52% of AML cases), leukemic blasts coexpressed the CD33 and CD64 antigens by a positivity of 60%. There were no significant correlations between the FAB subtype, clinical data (de novo or relapsed), or age group and the expression of CD33 and CD64 antigens in AML (p 0.05), however, most (21/32, i.e., 66%) of AML cases with monocytic element (M4 and M5) express higher levels of CD33/CD64 ( 60%). Conclusions: Considerable efforts have been made to identify molecular parameters, such as cytogenetic abnormalities, mutations, or cell surface markers as prognostic factors, in an effort to better stratify AML patients for adequate therapy. Immunophenotyping is not only helpful for diagnosis but is of independent significance for prognosis and may be useful for risk stratification in AML patients. An understanding of steps involved in the anti-CD33 X anti-CD64 BsAb-induced signaling cascade in myeloid cells is of potential clinical significance. Inhibition of leukemia cell growth initiated by BsAb may have therapeutic value for the treatment of AML and a direct inhibitory effect of the BsAb on AML cell proliferation and colony formation has been proved. Successful immunotherapy for cancer and in particular, mAb-based therapy are most likely to succeed first for the hematopoietic neoplasms because of their biology and because of the pharmacology of mAb and the availability of antibodies reactive with antigens expressed only by hematopoietic cells has provided clinical investigators with new tools for use in developing therapies for AML.