Viral delivery is a method used to introduce foreign genetic material into cells using viruses as vectors. Viruses have evolved to efficiently enter host cells and hijack the cellular machinery to replicate their own genetic material. Researchers have harnessed this ability to create recombinant viral vectors that can deliver specific genes or RNA molecules into target cells for various applications, such as gene therapy, gene editing, or basic research.

Common viral vectors used for gene delivery include:

1. Adenoviruses: These are double-stranded DNA viruses that can infect a wide range of cell types, including dividing and non-dividing cells. Adenoviral vectors have a large cloning capacity but do not integrate into the host genome, which reduces the risk of insertional mutagenesis. However, they can elicit strong immune responses, which may limit their use in some therapeutic applications.
2. Adeno-associated viruses (AAV): AAVs are small, single-stranded DNA viruses that can infect both dividing and non-dividing cells. AAV vectors have a lower cloning capacity compared to adenoviruses but are less immunogenic and can integrate into the host genome at specific sites with low risk of insertional mutagenesis. AAVs have been used in several successful gene therapy trials for inherited disorders, such as Leber’s congenital amaurosis and spinal muscular atrophy.
3. Lentiviruses: These are a subclass of retroviruses with single-stranded RNA genomes that can integrate into the host genome, making them suitable for stable gene expression in target cells. Lentiviral vectors can infect both dividing and non-dividing cells and have been used in gene therapy for diseases like severe combined immunodeficiency (SCID) and β-thalassemia.
4. Retroviruses: Like lentiviruses, retroviruses have single-stranded RNA genomes and can integrate into the host genome. However, they can only infect dividing cells, limiting their applicability in some cases. Retroviral vectors have been used in gene therapy for SCID and chronic granulomatous disease.

Viral delivery offers several advantages, such as high efficiency, stable gene expression, and the ability to target specific cell types using engineered viral tropism. However, it also has some drawbacks, including potential safety concerns (e.g., insertional mutagenesis or reversion to a replication-competent virus), limited cloning capacity for some vectors, and the possibility of immune responses against the viral vector.

Despite these challenges, viral delivery remains a powerful tool for gene transfer and has shown promise in the development of gene therapies for a variety of genetic disorders and other diseases.