Presence of a Flt-3 Internal Tandem Duplication in AML Blasts Predicts Inhibition of Differentiation towards Leukemic Dendritic Cells.

In the search for new treatment modalities to eradicate minimal residual disease cells (MRD) in acute myeloid leukemia (AML), immunotherapy provides an attractive option. AML blasts show differentiation towards leukemic dendritic cells (DC), providing the unique opportunity to generate DC harbouring the full range of tumour antigens. In a large cohort of AML samples (n=154) AML-DC were generated by two culture methods, i.e. in presence of cytokines GM-CSF, TNF-α, SCF, Flt-3L, IL-3 and IL-4 (n=147) or calcium ionophore (CI) and IL-4 (n=108). Median AML-DC yield, defined by phenotypical DC characteristics, in the cytokine-based cultures was 12% (range:0–70%). Considering cultures yielding ≥10% AML-DC successful, 58% (85/147) of cytokine-based cultures were successful and 61% (66/108) of CI cultures. Overall, functional AML-DC generated with either method was possible in 66% (101/154) of patients. Identification of AML blast populations with DC differentiation capacity is important to select patients eligible for immunisation programs. Interestingly, presence of Flt-3 internal tandem duplication (ITD) was strongly correlated with decreased DC differentiation capacity in both culture methods (cytokine-based culture: p<0.001; CI-culture: p=0.03) suggesting that constitutive activation of tyrosine kinase receptors inhibits differentiation towards DC. In multiparameter regression analysis, powerful predictors for cytokine-based AML-DC culture outcomes were Flt-3 ITD (regression coefficient B:-3.41, p<0.001), CD14 (B:3.28, p<0.001) and TNFα-RI (B:2.82, p<0.001). This regression model predicts 88% of culture outcomes. ROC curves show high sensitivity (95%) and specificity (76%) with an AUC of 0.93 (p<0.001). In 25% of unsuccessful cytokine-based cultures, the CI-based culture method provides an alternative. This percentage increases to 56% if Flt-3 ITD⁺ AML samples are left out, emphasizing Flt-3 ITD⁺ blasts’ inability to differentiate towards leukemic DC. In conclusion, AML-DC cultures are successful in most patients. Selection of patients is well possible based upon the presence of Flt-3 ITD and the expression of CD14 and TNFα-RI. Based on these results, we are currently entering patients in a phase I/II clinical vaccination trial.