Severe congenital neutropenia (CN) is a heterogeneous disorder of myelopoiesis which follows an autosomal dominant or autosomal recessive pattern of inheritance. Genetic analyses indicate mutations in the ELA2 gene in most patients. We have identified LEF-1 as a decisive transcription factor in granulopoiesis controlling proliferation and granulocytic differentiation by direct activation of its target gene, C/EBPalpha. In patients with CN, the expression of LEF-1 and C/EBPalpha was abrogated in myeloid progenitors leading to maturation arrest of granulopoiesis. In the present study we demonstrated that ELA2 mRNA expression in myeloid progenitors and plasma protein levels of neutrophil elastase (NE) were markedly reduced in patients with CN harboring mutations in either ELA2 or HAX-1 genes. The ELA2 gene promoter is positively regulated by the direct binding of LEF-1 or C/EBPalpha, documenting the role of LEF1 in the diminished ELA2 expression. We found that transduction of hematopoietic cells with LEF-1 cDNA resulted in the up-regulation of ELA2/NE synthesis, whereas inhibition of LEF-1 by shRNA led to a marked reduction in the levels of ELA2/NE. LEF-1 rescue of CD34(+) cells isolated from 2 patients with CN resulted in granulocytic differentiation of the cells which was in line with increased levels of functionally active ELA2/NE.