Helper dependent virus
（重定向自Replication defective virus）
A helper dependent virus also termed a gutless virus is a synthetic viral vector dependent on the assistance of a helper virus in order to replicate.
Hepatitis D virus (HDV) is an example of a replication defective, helper dependent ssRNA virus because it requires Hepatitis B virus (HBV) to provide HBV surface antigen (HBsAg) for the encapsidation of its genome. The envelope proteins on the outer surface of HDV are entirely provided by HBV.