dbDNA™: The Future of AAV Production
Recombinant adeno-associated virus (AAV) is one of the most promising delivery vehicles for genetic medicines, offering potential to treat a range of previously untreatable diseases. With hundreds of AAV-based therapies progressing through clinical trials, the demand for high-quality DNA starting material is high. But today’s AAV production still relies on plasmid DNA (pDNA), which brings with it challenges that slow progress and limit scalability.
In this blog, we take a closer look at the limitations of pDNA and explain how our dbDNA provides a promising alternative.
The challenges of plasmid-based AAV production
Today, the most common approach to manufacturing AAV is the co-transfection of HEK293 cells with three separate plasmids: one carrying the Rep and Cap genes for viral replication and capsid proteins, another providing adenoviral helper functions, and a third containing the therapeutic transgene flanked by inverted terminal repeats (ITRs). This system has been the gold standard of AAV research for years, but when it comes to clinical and commercial manufacturing, using pDNA introduces limitations.
Limited scalability
pDNA is produced in E. coli through bacterial fermentation, a process that is slow, expensive, resource-intensive and difficult to scale. Producing GMP-grade pDNA can take 10-12 months, as complex fermentation, purification and quality control steps all add time. With demand for AAV vectors rising rapidly, this lengthy production cycle is a serious bottleneck for the gene therapy field.
Poor fidelity
ITRs form cruciform secondary structures that are difficult to maintain in E. coli. During plasmid propagation, this structural instability can lead to deletions or rearrangements within the ITR regions, generating heterogeneous plasmid preparations. Compromised ITR integrity reduces the efficiency of viral rescue and packaging, resulting in lower and less consistent AAV yields.
Risk of antibiotic resistance
Because plasmids rely on antibiotic resistance markers for selection in bacterial systems, transfected plasmids can contain backbone sequences encoding antibiotic resistance genes. Plasmid-derived bacterial sequences are known to be inadvertently packaged into AAV capsids at frequencies ranging from 1-5%, and in some cases as high as 26%. This poses obvious safety concerns, as it risks transferring resistance traits. It also raises serious regulatory red flags, creating more hurdles for developers trying to move studies forward.
High manufacturing costs
On top of these issues, plasmid production in E. coli is expensive – most of the cost comes from time in GMP suites, specialist equipment, and the labour of highly trained staff. This reliance on resource-heavy facilities makes it difficult to expand capacity and to meet the growing demand for AAV vectors.
The solution: dbDNA™
At Touchlight, we’ve developed an advanced cell-free DNA technology platform that addresses the bottlenecks of plasmid-based AAV production. Our process is entirely in vitro and produces high-fidelity, covalently closed, linear DNA constructs, known as dbDNA.
Unlike pDNA, dbDNA is generated without bacteria and relies solely on enzymes. The process begins with a circular, double-stranded DNA molecule containing the sequence of interest, flanked by short protelomerase recognition sites. This template is amplified by Phi29 DNA polymerase through rolling circle amplification, producing concatemeric repeats of the construct with high fidelity. A protelomerase then cleaves and covalently closes the ends to generate monomeric, linear dbDNA. Residual bacterial backbone is removed by restriction digest and exonuclease, leaving only the dbDNA sequence of interest.
The resulting dbDNA offers several advantages for AAV production.
Superior purity and safety
dbDNA contains no bacterial backbone, meaning no antibiotic resistance genes and no risk of them being carried into AAV particles. The result is a high-purity DNA construct, free from unwanted genetic sequences that raise regulatory concerns and delay clinical development.
Faster timelines and scalable manufacturing
Because dbDNA is made entirely in vitro, it does not require large fermentation facilities or complex bacterial processes, which makes scaling simpler and less expensive. And with GMP-quality dbDNA produced in 2 weeks instead of the 10–12 months often needed for plasmids, it offers a faster, more economical way to meet growing demand.
Stable and consistent
dbDNA can amplify complex sequences with high fidelity, ensuring that ITRs remain stable. This eliminates the heterogeneity often seen in plasmid preparations, and stable ITRs in turn support more efficient replication and reliable packaging into viral particles.
Greater efficiency
dbDNA requires significantly less starting material to achieve equivalent or greater AAV titres compared with plasmids. In fact, dbDNA uses around 40% less DNA per transfection while delivering a more than two-fold increase in the proportion of full capsids. This “copy advantage” reduces input costs while supporting higher overall efficiency in vector production.
Summary
As gene therapy continues to advance, the limitations of plasmid-based AAV production threaten to slow progress and restrict patient access to life-changing treatments. Our dbDNA offers a way forward. By providing a faster, safer and more scalable source of DNA, dbDNA has the potential to resolve many of the major challenges facing AAV manufacturing. For the field of genetic medicine, this technology has the potential to transform how therapies are made and bring life-changing treatments to patients sooner.
Ready to bring your therapy to patients faster? Download our whitepaper and see how dbDNA AAV production streamlines your journey to the clinic.
