Helper-dependent adenovirus (HDAd), also known as Gutless adenovirus (GLAd), has been considered as the last-generation adenovirus. HDAd is constructed by deletion of all viral genes, resulting in no expression of adenoviral proteins. The only remained adenoviral sequences include ITRs, the adenoviral packaging signal, and a small untranscribed portion of the E4 region.

HDAd has many notable characteristics as a gene delivery vector. HDAd still retains the advantages of early generations of adenovirus such as a broad cell/tissue tropism, high infectivity, high transgene expression, and an absence of integration into the host genome. Since it is constructed following the deletion of all the adenoviral genes, HDAd exhibits a very large accommodation capacity for transgenes, which is approximately 30 kb, making it possible to deliver large genes as well as multiple genes. The absence of all adenoviral genes also enables HDAd to mediate long-term transgene expression in host organisms with minimal immunogenicity.