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Current Bottlenecks in CAR-T Therapies
The Growing Pains of Transient Transfection
Want to Get Ahead of the Curve?
Advanced therapies continue to push the boundaries of modern medicine. At the forefront, Chimeric Antigen Receptor-modified T-cell therapies (CAR-Ts) have demonstrated remarkable efficacy in several hematological cancer indications. And, the momentum is growing. Recent advancements in the field show promising results in treating autoimmune diseases and solid tumors, significantly expanding the patient population that could benefit from CAR-T therapies beyond hematological cancers.
However, as these therapies move from niche indications to broader patient populations, the demands placed on manufacturing platforms are evolving – and becoming more and more urgent.
Current Bottlenecks in CAR-T Therapies
Despite their therapeutic potential, CAR-T therapies face several key bottlenecks that continue to limit their broader application:
- Manufacturing Complexity & Scalability
- High Cost of Goods & Reimbursement Barriers
- Regulatory & Quality Challenges
These bottlenecks don´t just represent operational challenges, but they carry strategic risks that impact longterm success. Complexity of manufacturing drives up costs, which in turn affects pricing and reimbursement. Reimbursement barriers can significantly restrict patient access, especially in healthcare system under cost pressure. Scalability issues can delay timelines, limit patient access and can potentially render these groundbreaking therapies commercially unsustainable. In addition to that, regulatory compliance becomes increasingly difficult to maintain in a consistent manner due to the variability inherent in current manufacturing processes.
The consequences of these dynamics and challenges are already apparent. Many of the approved therapies are struggling to meet demand and a significant number of patients who could benefit from CAR-T therapy lack access. Even more concerning, several approved therapies have been withdrawn from the market – not due to lack of efficacy, but because their production and reimbursement models could not support long-term commercial viability. Not only do these barriers impact patients and providers, but also dampen confidence of investors slowing down the flow of capital into the field.
In this context, the choice of manufacturing platform isn´t just a technical decision – it is a core part of the therapy´s business case. One of the main cost drivers are lentiviral vectors (LVVs) which are necessary to deliver the CAR to the T-cell during manufacturing. LVVs alone make up approximately 30-50% of the total production costs of a CAR-T therapy. So let´s dive deeper into why LVV manufacturing, especially via transient transfection, is so complex and cost-intensive.
The Growing Pains of Transient Transfection
Most of the current therapies in clinical and commercial phase rely on transient transfection for LVV production. This process typically involves co-transfection of 3-4 plasmids - Gag/Pol, Rev, Envelope (often VSV-G) and the gene of interest (GOI)–into HEK293 cells, which then start producing the LVVs.
While this system allows for relatively fast and cost-effective early development, it also introduces a range of technical and economic challenges once projects require larger scales. Here are the major pain points that highlight why transient transfection remains a critical challenge:
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High Plasmid Costs:
Each plasmid needs to be produced under Good Manufacturing Practice (GMP) conditions at the right concentration and purity. Lead times for GMP plasmids can be long and they are rather expensive—accounting for roughly 30-50% of the total cost of goods of LVV production. -
Variability of Transfection:
Transfection is a sensitive process which is highly dependent on plasmid quality, ratios and mixing conditions as the plasmids need to be mixed in the correct ratios to ensure a consistent process. Even minor inconsistencies or deviations can affect efficiency of the process and therefore vector yield – and can even lead to full batch failures. This also increases the burden on QA/ QC as ensuring quality parameters like functional viral titer and empty/full ratio becomes more resource intensive. -
Scalability limitations:
At larger volumes, efficient mixing represents a major challenge. For example, transfection efficiency drops significantly in larger bioreactor volumes needed for late-stage or commercial-scale production, which limits scalability of this production system. -
Narrow Production Window:
Post-transfection, there is only a narrow production window of 48-72 hours. If efficiency of transfection is low, there is no mechanism for real-time correction. This in turn increases the risk of batch failure.
Platform Inflexibility
For therapy developers with multiple programs in their pipeline, transient transfection might represent a cost-effective and flexible solution – especially in early-stage development. In reality, using a new gene of interest soemtimes requires re-optimization of plasmid ratios and transfection conditions. This limits the ability to reuse process platforms across the development pipeline and can result in duplicated development efforts and additional regulatory submissions. Moreover, a potential tech transfer between internal teams and external stakeholders like manufacturers can become more error-prone, less predictable and slower, thus more expensive. Taking everything into account, what starts as a flexible, fast and cost-efficient solution can quickly become a bottleneck for broader commercialization.
The Case for Change
Transient transfection has enabled the current success of CAR-T and has served the field well by offering fast entry into clinic and flexibility in development with relatively small upfront investment. But this comes at the price of several disadvantages: multiple variable inputs, low batch consistency, high costs per batch, reduced platform reuse and severely limited scalability.
As advanced therapies move toward broader populations, one question remains:
Is transient transfection still a sustainable foundation for viral vector production?
It's Time to Evolve
While transient transfection enabled the first generation of CAR-T therapies and will continue to play a role in development pipelines, the industry needs to look ahead to enable production of the next generation of CAR-Ts. Forward-thinking biotech teams are already exploring smarter, more robust and scalable alternatives to minimize production risk, reduce costs, enable broader patient access and secure long-term viability.
As a CDMO committed to scalable innovation, it is our mission at ProBioGen to empower our partners to transcend the limitations of today´s platforms – as we build the manufacturing platforms of tomorrow.
In our next blog post, we’ll explore potential solutions to overcome current limitations of transient transfection-based production systems. Together, we will dive into which scalable alternatives could reshape the viral vector landscape and how they can address current bottlenecks.
Want to Get Ahead of the Curve?
Join us for our upcoming webinar on June 30 where our experts will discuss practical strategies for future-proof vector production – and how to leave the limitations of transient transfection behind.