As the gene therapy field matures, adeno-associated virus (AAV) manufacturing faces a turning point. For years, our industry has focused on rare and often lethal diseases: conditions where even imperfect processes were acceptable because no alternatives existed. But today, we’re seeing a shift (Fig 1). AAV therapeutics are advancing toward non-rare indications such as Parkinson’s, Alzheimer’s, certain cancers, diabetic conditions with genetic origins, and more. These diseases represent huge patient populations, and with that shift comes new scrutiny on cost, safety, and scalability.
Fig 1. A comparison of diseases targeted by AAV therapeutics in use and in development. Approximately 60% of these therapeutics are for non-rare diseases. Source: Global Data 2026
From conversations with manufacturers, panel discussions, and direct experience in AAV development, three pain points rise to the top: yield, quality, and cost. These are not new challenges. But the scale of the need has changed dramatically. As we push toward more accessible AAV therapeutics, we must rethink our approach, starting with upstream processing.
Why non-rare AAV changes everything
Unlike rare disease applications, non-rare indications require therapies that are:
- Manufacturable at very large scale (500 to 2000 L batches or more)
- Extremely safe, because patients aren’t facing imminent life-threatening outcomes
- Cost-effective, not only for therapy developers but for entire health systems
In rare diseases, a gene therapy dose may cost $1M to $3.5M. For non-rare diseases, that cost simply isn’t viable. To expand access, we need to reduce the cost per dose by 10- to 100-fold. Probably closer to 100-fold range. Manufacturing contributes to this reduction, but it’s only a fraction of the total cost. One of the largest contributors to high therapy cost is the need to “depreciate” the development of all the failed or discontinued drug candidates over the few that make it to market.
But even with these broader economic factors at play, manufacturing remains foundational. It’s the part we can control. And it starts upstream.
The upstream problem: yield and quality still limit what’s possible
When I ask teams about their biggest manufacturing challenges, the answer is almost universal: yields and quality. These two parameters—how much vector you make and how good it is—dictate your entire downstream strategy. And they dictate your costs.
A common misconception is that downstream can fix everything. It can’t.
I often use a cooking analogy: You can have the world’s best chef, tools, and plating… but if the ingredients aren’t good, the dish won’t be either. Downstream processing is the chef. Upstream results are your ingredients.
If upstream AAV production delivers low titer, poor full-to-empty capsid ratio, inconsistent potency, and/or high impurity burden, then downstream becomes a bottleneck and a cost driver. It’s not a magical tool that can turn empties into full particles or improve potency. In fact, low full-to-empty ratio is one of the biggest sources of waste: you may end up capturing and purifying 80% empty particles, consuming hardware, buffers, and time for material that will be discarded later.
That’s why improving upstream AAV productivity and quality matters so much; it fundamentally changes the economics of the entire process.
How we improve: cell lines, media, process optimization, and boosters
Full-to-empty ratio, productivity, and scalability require multiparametric optimization. Teams typically work on:
- Improving producer cell lines
- Media optimization
- Culture strategies (batch, fed-batch, perfusion)
- Upstream additives like enhancers or boosters
- High-quality plasmid DNA, which is critical for yield
No bioreactor can compensate for poor pDNA quality or subpar upstream conditions. This is where cell culture boosters can have a significant role. Boosters increase the productivity of your cell line. Although boosters are not the only upstream tool available, they are simple to implement and can be highly impactful for teams trying to maximize output at their current scale. A good booster is also compatible across platforms and may be used with a variety of cell lines and media.
Imagine a booster that can double productivity in upstream AAV manufacturing. That two-fold increase doesn't double your batch cost—far from it. Instead, it increases the amount of product you can generate without proportionally increasing consumables, labor, or time. Doubling upstream yield is not the sole answer, but it’s a meaningful step toward making non-rare AAV economically viable.
A cell booster aims to replenish key nutrients that are critical to viral production, which get rapidly consumed once viral production is triggered. This replenishment leads to an increase of virus productivity per cell. On the other hand, enhancers change the cell biology kinetics to shift away from proliferation metabolism to production pathways. Thus, the benefits you may see from using an enhancer or booster may include higher yield, more consistent results, and easier scale-up. Any of these improvements will also move you toward economic viability. Boosters and enhancers are often used in combination because they likely will have different mechanisms of action.
Beyond transient: why producer cell lines matter for non-rare AAV
As we scale toward treating larger populations, variability becomes our enemy. Transient transfection workflows rely on multiple plasmids entering a cell with the right stoichiometry. It’s inherently probabilistic and expensive.
Producer cell lines remove this variability by embedding the necessary components directly into the cell line. This combination brings several advantages:
- No more plasmid supply constraints or costs
- Dramatically increased robustness
- Streamlined scale-up
- Predictable output batch after batch
For non-rare diseases, producer cell lines are not just an efficiency improvement. They are a requirement for long-term manufacturing sustainability.
A call to developers: start with the end in mind
If I could give one piece of advice to teams working on AAV today, it would be this:
Design your process based on the scale and requirements of your final clinical application not your current research need.
Too many teams build processes just good enough to raise money, only to encounter delays and high costs when CDMOs must later rework the process for scalability and robustness.
Other strategic moves to implement are:
- Optimize upstream early with a clear focus on yield and full-to-empty ratio
- Adopt scalable technologies (media, supplements, fed batch or perfusion processes when applicable, producer cell lines)
- Invest in high-quality pDNA and well-designed constructs
Starting with the end in mind saves time, reduces risk, and avoids costly redevelopment later.
Final thoughts: accessibility depends on developers
As we move toward non-rare AAV therapeutics, the conversation shifts from “How do we treat a few hundred patients?” to “How do we treat hundreds of thousands?”
Non-rare AAV therapies have exciting potential. But this potential leads to enormous responsibility. We must build manufacturing processes that scale efficiently, reduce costs, guarantee safety, and enable broad global accessibility.
Upstream innovation, including productivity boosters and enhancers, robust producer cell lines, and optimized processes, is key to meeting the accessibility challenge.
We’re on the brink of transforming how many people gene therapy can reach. To make that promise real, we need to rethink AAV manufacturing from the top down starting with yield, quality, and smart upstream design.