Cytomegalovirus (CMV), is a genus of Herpes viruses; in humans the species is known as Human herpesvirus 5 (HHV-5). It belongs to the Betaherpesvirinae subfamily of Herpesviridae. The name means "very big cell virus". Human cytomegalovirus ICP22 is the product of the HWLF1 reading frame and is an early nuclear protein that is released from cells. ICP22 was readily detected as a β (delayed early) gene product during viral growth.