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Introduction To Adeno-Associated Viruses (AAV)

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Since researchers have discovered DNA as a genetic inheritance of biomolecule and disease, it has dug up the therapies prospects in which there could be an alteration of mutant and damaged genes in improving the condition of humans. As a result, there have been efforts to carry out human genetics more cheaply and rapidly on so many people, and to sequence, complete genomes have made researchers to nuclei acid sequence information explosion. This has allowed them in identifying the gene or genes that may drive a specific state of disease. If there could be fixing of the mutant gene(s) or if there could be normalisation of genes that overperform or not active could, the treatment of the disease could be at a molecular level. And in the best case, there may be a potential cure. However, this concept does not seem to be a lie in monogenic disease treatment, that is, a disease that comes from single-gene mutations. For more than four decades, this simple premise has been the objective of gene therapy. 

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What is AAV?

The year 1975 was the discovery year of the first adeno-associated virus, known as AAV. It was discovered as an adenovirus (Ad) preparations-contaminant, hence, the name. The adeno-associated virus remains one of the smallest viruses with a non-enveloped capsid of approximately 22 nm. However, sero-positive with AAV2 is very common in adults, and there has been no connection with any disease or symptoms. Although 80-90% of adults are sero-positive with AAV2, the infection has not been associated with any symptoms or disease. Many researchers opt for the best AAV packaging services to help them get the desired outcome in their experiment. 

AAV Immunogenicity

Researchers find using rAAV to be appealing, but they are concerned most with applying it as a transfer of gene vector. This is because it comprises biomolecules, that is, proteins and nucleic acid. Thankfully, there is no engineered lipid or other chemical components in a full-packaged virus that could lead to contributing to needless immunogenicities or toxicities that comes with difficulty to predict or understand. Generally, adeno-associated viruses have proved to have lesser immunogenicity, unlike tiger viruses. 

However, its full understanding remains unclear and a likely reason may be based on the observation that some AAVs do not have effecient transduction of antigen-presenting cells (APCs) [65]. Moreover, rAAV has no viral genes unlike previous strategies of viral delivery. Therefore, to amplify the response of the immune, there will be zero expression of a viral gene. When compared to other viruses, AAV has shown to have poor immunogenicity features, that is, it is an adenovirus and the capsid proteins and nucleic acid sequence are delivered, triggering the immune system’s various parts.

AAV Tropisms

Without doubts, the AAV stereotype for in vitro and in vivo gene delivery remains the most sought-after. However, there has been the isolation of other different AAV stereotypes and yearly, the discovery of new serotypes. Some of these serotypes include AAV1, AAV2, AAV5, as well as AAV7, 8, and lots more. All of them have been employed for studying gene delivery. Most researchers may often wonder which is the best and appropriate for a specific model of gene. 

Although several studies have been focused on the comparison between the efficacy of delivery of genes on different models, however, there are often controversies in the data, if not conflicting. It remains unclear why this happens. Different factors, such as involvement of animal species, study protocols, end-point readout, organs or organs, including the measures employed used in preparing these recombinant viruses. All these factors may have contributed to the conflicting data. Comparing the efficacy of delivery of gene by many. Comparing the efficacy of delivery of gene may be a good idea if possible by many rAAVs carrying a reporter gene such as FP or LacZ, to come up with the best serotype and the most suitable strategy for carrying out certain studies by researchers. 

The importance of AAV in research 

For optogenetics, researchers employ AAV in most cases, especially AAV production and purification because they remain primarily episomal, hence, they are the best choices over other kinds of viruses, including lentiviruses. However, lentiviruses integrate into the game. Adeno-associated virus vectors can transduce a different range of both dividing and non-dividing cell types. This is why these vectors have remained crucial in the therapy of genes. One major importance researchers derive from it is the ability to express transgenes that can obtain after the delivery of the vivo gene. 

Production of Adeno-associated virus

AAV production comes from packaging cell lines following transfection of the AAV construct as well as co-infection with a helper virus, such as adenovirus (Ad) or Herpes Simplex Virus (HSV) or via a single infection with a recombinant helper viral vector containing the rAAV genome.

Advantages of AAV

  • It comes with a top-notch biosafety rating. They do not cause disease of any type, including the wild types in vivo 
  • Their immunogenicity is very low as they cause a very mild immune response in vivo, providing more support to its apparent absence of pathogenicity during the delivery of the gene. 

Drawbacks of AAV-mediated gene transfer

Adeno-associated virus is beneficial to research, and at the same time, it comes with some drawbacks. 

  • The cloning capacity of AAV is limited, (less than 4.7kb of the vector. This prevents its use in delivering genes of large genes. 
  • Neutralizing antibodies generation against AAV in the Non-Human Primates (NHP) and humans, may beef up the cure effect of AAV-mediated gene therapy

Conclusion

Getting the right AAV packaging system can help to have a better research outcome. However, AAV can help achieve a  better outcome in research work since they do not associate with causing any disease. 

 

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