Despite many improvements in management of different disorders, development of effective and durable treatments has proven to be challenging. Genetic interventions may resolve these limitations. A large number of gene delivery methods have been developed using viral and non-viral vectors, each of which have their own pros and cons. Non-viral vectors are typically easy to synthesize and can transfer genetic material of different sizes. Major limitations of non-viral vectors are their very low in vivo gene transfer activity and their difficulty to transduce differentiated cells. Viral vectors are much better suited for this purpose. The most commonly used viral vectors are derived from lentiviruses, adenoviruses and adeno-associated viruses. Genome of lentivirus vectors (LVs) is integrated into the host cell genome and they accommodate a fair amount of foreign DNA. LVs are much less suitable for in vivo gene therapies due to their large diameter. Adenoviral vectors (AdVs) can be produced in large quantities and very efficiently transduce all kinds of cells. The main disadvantages of AdVs are their large size and their high immunogenicity. Adeno-associated virus vectors (AAVs) are significantly less immunogenic than AdVs and can mediate long-term gene expression. Their small diameter, allows them to easily penetrate tissues. Low gene transfer activity and limited packaging capacity are disadvantages of AAVs. Conclusion: Challenges attributable to inefficient gene delivery system, immune responses and low transgene expression, hampering clinical application of vectors. Therefore, the development of safe, effective, and clinically applicable gene transfer techniques will improve the current therapies in the clinic.

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