Comparing Gene Transfer Tools: Adeno-Associated Virus and Lentiviral Vectors

Gene therapies have evolved significantly over the past several years, largely thanks to viral vectors.

Adeno-associated virus (AAV) and lentivirus (LV) vectors are increasingly prominent in the gene transfer space. The vectors account for half of the current vector-related clinical trials worldwide, according to research published in Signal Transduction and Targeted Therapy. The other half? Adenoviruses, a research mainstay with concerns about immunogenicity.

AAV and LV vectors can be appealing alternatives to adenoviruses for researchers engaged in viral vector work. For one, they can each infect dividing and nondividing cells. There's also less risk of a significant immune response from the host.

But despite their similarities, their differences affect applications and workflows, especially regarding purity and viability.

The Pros and Cons of Adeno-Associated Virus Vectors

An AAV is a dependoparvovirus that generally relies on an adenovirus or another helper virus for its genetic expression. With an extensive viral tropism profile, an AAV vector is particularly beneficial as a transfer mechanism for gene therapies involving the heart, liver, and central nervous system, Signal Transduction and Targeted Therapy notes.

And yet AAVs are not optimal for every scenario — and especially not for research performed in vitro. Transduction behavior in vitro doesn't always predict in vivo response; that requires more research involving nonhuman primates before reaching clinical trials. AAV vectors are also limited by package size, with a max of about 5 kilobases.

The Pros and Cons of Lentiviral Vectors

As a retrovirus subtype, LV vectors, such as those derived from HIV, are known for their ability to integrate within the genome and for their large capacity, which enables multigene expression. They can also be studied in vitro. These advantages make LV vectors a common choice for complex disease states such as cancers, immune and metabolic disorders, and congenital diseases.

However, as Signal Transduction and Targeted Therapy notes, LV vectors have historically carried the risk of insertional mutagenesis, though this risk can be minimized by using third-generation, self-inactivating LV vectors.

Purification and Viability of Adeno-Associated Virus and Lentiviral Vectors

AAV and LV vectors have safety and operational challenges with downstream purification, but requirements vary by vehicle type. As noted in Scientific Reports, AAVs generally require cellular lysis, which can leave behind contaminants from host cells. AAV vector production is also prone to incomplete and empty viral capsids, which can also carry contamination risks. On the other hand, LV vectors could require a more involved or restrictive processing workflow to reach desired yield and purity, according to research published in Cell.

Because of these and other concerns, researchers are increasingly deploying closed and semi-automated systems for bioburden and processing control. Automation tools embedded in these systems reduce manual processing and handling steps, which can mitigate AAV vectors' contamination risks and address LV vectors' workflow needs. Closed systems also can reduce environmental contamination risks.

Researchers are also looking at high-yield platforms for adherent cultures — including products like Corning CellSTACK® culture chambers and HYPERStack® vessels, which can make for more efficient scale-up, Cell Culture Dish says. These products, and the next generation fixed-bed bioreactors like Corning Ascent® Fixed Bed Reactor offer increased surface area to volume ratio in a smaller footprint, increasing scale potential and providing automated control in closed systems.

Finding What Works for You

Every tool has its ideal applications. AAV and LV vectors are no different: Each gene transfer mechanism has advantages, disadvantages, and scaling considerations. Fortunately, researchers have options these days — and the more advances made in gene therapies, the more promising the future looks for patients who need them.