Summary of a Nature Biotechnology article titled "Big pharma buys into exosomes for drug delivery":
What problems could exosomes solve? Currently, viruses such as AAV (Adeno-associated virus) and lipid nanoparticle are popular vectors that are used to deliver nucleic acids to cells in gene and RNA therapies. A limitation to their usage, however, is immunogenicity*. Exosomes don't elicit any immune responses as they are naturally occurring vesicles.
What are other advantages of exosomes? AAV vectors can carry up to five kilobases, whereas presumably exosomes can carry more and bigger molecules in them. Targetability is another strength of exosomes. They could be engineered in a way that they bind to specific cells, delivering cargoes to target cells.
Any competitors to exosomes? Alnylam uses N-acetylgalactosamine conjugates to deliver the company's siRNA drugs (i.e. Givlaari (givosiran) and Lumasiran (Oxlumo)) to the liver. Would we be able to engineer viral vectors and lipid nanoparticles so that they could evade immune detection and target specific cells? Maybe. Something to keep watching.
* For example, some experts raised questions whether the viral vectors could account for the low efficiencies of Astrazeneca-Oxford COVID-10 vaccine (with the full dosage) and Sinopharm's COVID-19 vaccine (in people aged 60 years and older). Moreover, a patient who had an AAV-based gene therapy cannot get the treatment with the same vector again since they already established immunity to the AAV vector.