Which vector uses DNA for gene delivery but does not integrate into the host genome?

Adenovirus is the correct answer because it is a type of viral vector that delivers genetic material into host cells without integrating into the host genome. Upon entry, adenoviruses primarily exist as episomes, which are circular DNA molecules within the nucleus, rather than incorporating their DNA into the chromosomal DNA of the host. This characteristic makes adenoviruses useful for transient gene expression since the delivered genes do not alter the host’s genetic material permanently.

In contrast, retroviruses integrate their genetic material into the host genome, which can result in stable and long-term gene expression but may have implications for genomic stability. Adeno-associated viruses can integrate into the host genome under specific conditions, though they are primarily known for stable transduction. Naked DNA refers to the direct introduction of plasmid DNA into cells, which does not rely on a viral vector, but it is not considered a vector in the same context as adenoviruses or other viral delivery systems.