Transcription factor required for TBX21/T-bet-dependent maturation of Th1 cells as well as maintenance of Th1-specific gene expression. Involved in embryogenesis and hematopoiesis. Expressed in Th1 cells, CD8-positive T-cells, B-cells and NK cells. By TBX21 in developing as well as mature Th1 cells. Th1 cells lacking Hlx or Tbx21 fail to express normal levels of the Th1-specific cytokine Ifng. Belongs to the H2.0 homeobox family.