AAV Engineering for Improving Tropism to the Central Nervous System

Abstract

Adeno-associated virus (AAV) is a non-pathogenic virus that mainly infects primates with the help of adenoviruses. AAV is being widely used as a delivery vector for in vivo gene therapy, as evidenced by five currently approved drugs and more than 255 clinical trials across the world. Due to its relatively low immunogenicity and toxicity, sustained efficacy, and broad tropism, AAV holds great promise for treating many indications, including central nervous system (CNS), ocular, muscular, and liver diseases. However, low delivery efficiency, especially for the CNS due to the blood-brain barrier (BBB), remains a significant challenge for more clinical application of AAV gene therapy. Thus, there is an urgent need for utilizing AAV engineering to discover next-generation capsids with improved properties, e.g., enhanced BBB penetrance, lower immunogenicity, and higher packaging efficiency. AAV engineering methods, including directed evolution, rational design, and in silico design, have been developed, resulting in the discovery of novel capsids (e.g., PhP.B, B10, PAL1A/B/C). In this review, we discuss key studies that identified engineered CNS capsids and/or established methodological improvements. Further, we also discussed important issues that need to be addressed, including cross-species translatability, cell specificity, and modular engineering to improve multiple properties simultaneously.

Enhancing the production of adeno‐associated virus (AAV)2 and AAV9 with high full capsid ratio in HEK293 cells through design‐of‐experiment optimization of triple plasmid ratio

“…Subsequently, the processed and replicated AAV genomes are packaged into assembled capsids by the Rep52/40 complex. [6,[13][14][15]25,26] Different ratios of helper RNAs, Rep proteins, Cap proteins, and pAAV-GOI DNA molecules can affect the assembly of AAV particles. Therefore, the triple plasmid ratio is likely to affect the genome titer and full capsid ratio.…”

“…[1][2][3][4][5] To date, six AAV-based gene therapies have been approved for clinical use by regulatory agencies and more than 255 clinical trials have been conducted or are ongoing. [6] To date, more than 100 AAV serotypes, including synthetic serotypes, have been identified that exhibit various tropisms and characteristics in human tissues. [2,7] Thus, AAV serotypes for gene therapy are selected according to the target tissues.…”

“…[ 1–5 ] To date, six AAV‐based gene therapies have been approved for clinical use by regulatory agencies and more than 255 clinical trials have been conducted or are ongoing. [ 6 ]…”

Gene replacement therapies for inherited disorders of neurotransmission: Current progress in succinic semialdehyde dehydrogenase deficiency

“…Remarkably, machine learning approaches are being deployed in the rational design and identification of nextgeneration viral vectors for higher transduction efficiency, improved tropism, and low toxicity. [76][77][78] The use of novel machine learning algorithms such as large language models 79 might further facilitate such rational design of viral vector capsid 80 and therapeutic payload. 81…”

Optoelectronic control of cardiac rhythm: Toward shock‐free ambulatory cardioversion of atrial fibrillation

“…Nevertheless, such an approach in patients would require a very large number of vector particles and is therefore unlikely to be pursued in the near future given the (prohibitively) high costs of vector production and the undesired spreading of vectors beyond the targeted tissue. This situation may change with the further sophistication of methods to select/engineer new, highly cell type-specific AAV capsids [86,87]. As mentioned above, the application of viral vector particles directly onto the epicardial side of the atria through "gene painting" offers a potential alternative to systemic injection.…”