HOXA9 and acute myeloid leukemia: IRX3 is co-expressed with HOXA genes in primary AML samples, in particular in cases with a normal karyotype or with mutations in NPM1 and/or FLT3. Functional experiments demonstrated that IRX3 expression alone is sufficient to immortalize murine hematopoietic stem and progenitor cells in vitro, and in vivo it collaborates with Hoxa9 to confer a differentiation block in murine AML.11