FLT3-ITD DNA and MRNA Levels in AML Do Not Correlate with CD7, CD33 and CD123 Expression

Introduction: FLT3 internal tandem duplication (ITD) mutations are found in around 25% of all acute myeloid leukaemia (AML) cases and is associated with shorter disease-free and overall survival. Previous reports have shown that FLT3-ITD induces a specific phenotype in leukemic blasts, which is characterized by high levels of CD33 and CD123, and that expression of CD33 and CD123 is directly influenced by the DNA FLT3-ITD/wild-type FLT3 allelic ratio (AR).

Methods: A total of 42 FLT3-ITD and 104 FLT3-ITD-negative AML patients were analysed. Immunophenotyping data were used to calculate antigen expression levels as the ratio between the geometric mean fluorescence intensities (MFIs) of leukemic blasts and MFIs of negative lymphocyte populations. FLT3-ITD-DNA and RNA analysis was performed, under the same conditions, by capillary electrophoresis.

Results: Compared with the control group, the FLT3-ITD cohort presented significantly higher CD7, CD33 and CD123 levels. In order to assess the impact of FLT3-ITD abundance on antigen expression, the patients were grouped for each parameter into two cohorts using the following threshold values: (a) 0.5 for the AR, according to current AML guidelines; (b) 0.7 for the FLT3-ITD/FLT3-WT mRNA ratio (RR); and (c) 1.3 for the FLT3-ITD RR/AR ratio. We found higher values of CD33 for RR/AR ≥1.3, and no other statistical differences between CD7, CD33 and CD123 levels of the other FLT3-ITD groups. In terms of correlations between MFI values and FLT3-ITD parameters, we only observed a moderate interdependence between CD33 MFI and the RR/AR ratio, and a weak negative correlation between CD123 MFI and AR.

Conclusion: FLT3-ITD mutations induce a specific antigen profile in AML blasts, and our data do not onfirm previous reports of FLT3-ITD AR influencing both CD33 and CD123 expression.