FLT3 receptor/CD135 expression by flow cytometry in acute myeloid leukemia: Relation to FLT3 gene mutations and mRNA transcripts

Abstract

Background: Alterations of the FLT3 gene are the most frequent molecular aberrations seen at diagnosis of acute myeloid leukemia (AML). Two main types of FLT3 mutations have been the most commonly detected; internal tandem duplication (ITD) in the juxtamembrane domain and point mutation D835Y in the tyrosine kinase domain (TKD). Both classes of mutations result in constitutive activation of FLT3 receptor/CD135.

Aim: To assess the frequency of FLT3 gene mutations (ITD and TKD D835Y) and the flow cytometric expression of FLT3 receptor/CD135 among AML patients to define the role for FLT3 receptor expression in predicting FLT3 gene mutational status and mRNA transcript level.

Subjects and methods: Eighty AML patients at diagnosis and 20 control subjects were enrolled. FLT3 receptor/ CD135 expression, FLT3 gene mutations, and FLT3 transcript level were evaluated by flow cytometry, conventional polymerase chain reaction (PCR), and quantitative real-time reverse-transcription PCR, respectively. Fluorescence in situ hybridization was done to stratify patients into favorable, intermediate, and poor cytogenetic risk groups.

Results: FLT3-ITD was detected in 22.5% AML patients, while none had FLT3-TKD D835Y mutation. A cutoff value of >17% was assigned to define FLT3 receptor/CD135⁺ cases. FLT3 receptor/CD135 and FLT3 transcripts were overexpressed in 100% AML patients; higher levels were found among AML-M5 subtype and poor cytogenetic group. AML patients harboring FLT3-ITD showed a trend for higher FLT3 receptor/CD135 expression and FLT3 transcript level than those with wild-type FLT3. FLT3 receptor/CD135 >49% was predictive for FLT3-ITD. A positive correlation was found between FLT3 receptor/CD135 expression and FLT3 transcript level.

Conclusion: Evaluation of FLT3 receptor/CD135 expression by flow cytometry at diagnosis of AML could constitute a predictor for the FLT3-ITD mutational status and FLT3 transcript level.

Keywords: Acute myeloid leukemia, CD135, FLT3 receptor, FLT3 mRNA, FLT3-ITD, FLT3-TKD