Complex sentence: HHV Infected Cell Polypeptide 0 (ICP0) (sometimes "Infected Cell Protein 0") is a protein produced by Herpes viruses during the earliest stage of infection, when the herpes virus has recently entered the host cell.
Split into simpler sentences: HHV Infected Cell Polypeptide ICP0 (sometimes "Infected Cell Protein 0") is a protein found in Herpes viruses. ICP0 is produced and functions at the earliest stage of infection, when the herpes virus has recently entered the host cell.