TLE4 is a repressor of the oncogenic activity of TLX3 in T-cell acute lymphoblastic leukemia.

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive hematological disease originating from the malignant transformation of T-cell progenitors, caused by the accumulation of genetic aberrations. One-fifth of T-ALL patients are characterized by ectopic expression of the homeobox transcription factor TLX3. However, the role of TLX3 in T-ALL remains elusive, partly due to the lack of suitable study models. Strikingly, this TLX3-positive subgroup has a high frequency of FLT3 mutations, predominantly FLT3-ITD, in pediatric cases. To investigate this, we generated ex vivo cultured pro-T cells driven by the co-expression of TLX3 and FLT3-ITD, which conferred IL7 independent growth. This model allowed us to confirm that TLX3 expression and FLT3 signaling cooperate to transform T-cells and induce an oncogenic context. Data from this cell model, combined with gene expression data from TLX3 positive T-ALL cases, revealed a strong downregulation of the transcriptional repressor TLE4. Furthermore, TLE4 showed to have a repressive effect on ex vivo TLX3 T-ALL cell growth, likely caused by a partial reversal of the TLX3 transcriptional profile. In conclusion, we developed a TLX3+FLT3-ITD pro-T cell model and used it to illustrate that TLX3 directly represses TLE4 expression, which is beneficial for the oncogenic function of TLX3.