HOXB4 is a sequence-specific transcription factor of the Antp (short for Antennapedia, from the Drosophila ortholog) homeobox family. It is expressed in early development and has been shown to facilitate expansion of hematopoietic stem cells. Human HOXB4 is a predicted 27 kDa protein with a proline-rich domain, an Antp hexapeptide VVYPWM, and a DNA-binding homeodomain. Human HOXB4 shows 95% aa identity with mouse HOXB4.