HOXB4 protein is a transcription factor encoded by the HOXB4 gene within the HOXB gene cluster of the homeobox gene family.During embryonic development, HOXB4 plays a pivotal role in anterior - posterior (A - P) axis patterning. In hematopoiesis, HOXB4 is a key regulator. It promotes the self - renewal of hematopoietic stem cells (HSCs). Besides,Sex Determining Region Y Box Protein 2 (SOX2) has been identified as an interactor of HOXB4, thus a functional binding ELISA assay was conducted to detect the interaction of recombinant human HOXB4 and recombinant human SOX2 . Briefly, biotin-linked HOXB4 were diluted serially in PBS, with 0.01% BSA (pH 7.4). Duplicate samples of 100μl were then transferred to SOX2-coated microtiter wells and incubated for 1h at 37℃. Wells were washed with PBST 3 times and incubation with Streptavidin-HRP for 30min, then wells were aspirated and washed 5 times. With the addition of substrate solution, wells were incubated 15-25 minutes at 37℃. Finally, add 50µl stop solution to the wells and read at 450nm immediately. The binding activity of HOXB4 and SOX2 was shown in Figure 1, the EC50 for this effect is 0.044ug/mL.