Instructive role of MLL fusion proteins revealed by a faithful model of t(4;11) proB acute lymphoblastic leukemia

The t(4;11)(q21;q23) fuses MLL to AF4, the most common MLL fusion partner. Here we show that MLL fused to murine Af4, highly conserved with human AF4, produces high-titer retrovirus permitting efficient transduction of human CD34+ cells to generate a faithful model of t(4;11) proB ALL that fully recapitulates the immunophenotypic and molecular aspects of the disease. MLL-Af4 induces a distinct B-ALL from MLL-AF9 through differential DNA binding of the fusion proteins leading to specific gene expression patterns. MLL-Af4 cells can assume a myeloid state under environmental pressure but retain lymphoid-lineage potential. We observed this incongruity in t(4;11) patients who evaded CD19-directed therapy by undergoing myeloid-lineage switch. Our model provides a valuable tool to unravel the pathogenesis of MLL-AF4 leukemogenesis. Overall design: MLL-AF4 ChIP-seq expreiment has been used in this study