The promise of in vivo CAR T is easy to understand. Instead of removing a patient's cells, engineering them in a manufacturing facility, and returning them to the body, developers are working toward delivering the machinery needed to create CAR T cells directly inside the patient.
If successful, the approach could remove some of the most difficult steps in conventional cell therapy manufacturing. It could potentially make therapies faster to produce, less expensive, and easier to deliver, making cell and gene therapies more accessible to a broader patient population.
That potential has generated significant excitement around in vivo approaches. But what does this mean for ex vivo CAR T?
For all the attention surrounding in vivo approaches, ex vivo CAR T has a much stronger clinical track record, with multiple commercial products approved by the FDA since 2017 to treat blood cancers. Additionally, the very features that make ex vivo manufacturing complex can also give developers something that is difficult to replicate when engineering cells inside the body — control.
The question facing the field is not whether in vivo will replace ex vivo, but where each approach makes the most sense and how far ex vivo manufacturing can be improved in the meantime.
“Both kind of approaches will coexist, and what is important is to identify which is the one to be used for every specific therapeutic. So, it’s not that much in vivo versus ex vivo, it’s more like having the right technology for the right therapy,” Natalia Elizalde, Chief Business Development Officer at VIVEbiotech, told DDN.
Where ex vivo still has an advantage
The strongest argument for ex vivo is that developers can control the cells before putting them into the patient. For example, CAR T products contain different T cell populations with different functions. CD8+ T cells are important for directly killing target cells, while CD4+ T cells can provide helper functions that influence T cell health and expansion.
With an ex vivo process, developers can select and manipulate these populations and control the conditions under which they are engineered and expanded. That creates opportunities to optimize the composition and characteristics of the final product.
“If you look at the approved products and some of the late-stage trials, you can see that you can achieve 90-plus percent efficacy, which is very, very difficult to achieve with other modalities, precisely because ex vivo CAR T has such rigid control of the manufacturing process,” Sophie He, Cell Therapy Leader at Bracco, told DDN.
He also emphasized that in vivo CAR T is still an emerging technology. “There are a lot of strategies being developed to address some very challenging questions, such as where the material ends up. Does it go to the liver, or is it delivered where you want it to be? Is the transfection sufficient and effective in the human body compared with what you observed in vitro or in animal models? And can you control the safety in the human body, where patients are very different from healthy volunteers?”
The ability to control the cells is a major advantage, but it also creates the central manufacturing challenge for ex vivo CAR T. Every additional step performed outside the body adds time, cost, and opportunities for variability.
Making ex vivo faster and more reproducible
Manufacturers are still trying to address almost every part of the workflow that makes ex vivo CAR T difficult, including cost, manufacturing time, variability, labor requirements, contamination risk, and the difficulty of scaling personalized production.
“The reason why CAR T takes so much time and costs so much is because a lot of the commercialized products are still produced largely manually or semi-manually,” said He. Even when parts of the manufacturing workflow are contained within closed systems, operators may still need to intervene to transfer materials between devices. This adds cleanroom, labor, and training requirements while increasing the potential for process variability and contamination.
Jerry Huang, APAC Marketing Manager, Cell Therapy Technologies for Terumo Blood and Cell Technologies, told DDN that reducing the transfers and manual interventions between steps could be one of the biggest opportunities for optimization. “If you break down the CAR T manufacturing process, there are a dozen or more individual steps in the whole manufacturing process, but functionally, I think they can be grouped into four major manufacturing modules,” he said.
Huang suggested that the CAR T manufacturing workflow could be divided into four functional modules: cell collection, T cell isolation, cell engineering, and fill-finish. Terumo BCT is already working towards this. In 2025, they published a protocol developed with Eureka Biotechnology that integrated three cell engineering steps including T cell activation, viral transduction, and expansion into one closed workflow. Using this system, they produced more than 12 billion CAR T cells in seven to eight days, while achieving a two-fold increase in transduction efficiency compared with manual culture.
The reason why CAR T takes so much time and costs so much is because a lot of the commercialized products are still produced largely manually or semi-manually.
—Sophie He, Bracco
This is just one example of the many advances being made to improve ex vivo CAR T across the entire manufacturing workflow. “The other innovation that most people are very excited about in terms of automation is rapid-release quality control,” said He. “At the end, to satisfy regulatory requirements, we still have to demonstrate that the final product has been properly characterized and is free from contamination. The final product release can take two to four weeks. If you can do that faster, that can definitely help in terms of the vein-to-vein process.”
But automation can only solve part of the problem. The process also depends on the quality of the cells collected from each patient.
Better cells, better processes
Unlike healthy donor cells used during process development, cells collected from patients can vary considerably in quality and quantity. If there are not enough healthy T cells at the beginning of the process, it can become difficult to generate sufficient numbers of functional CAR T cells for treatment.
“For patients, the starting cell number is very important. One of the reasons why some products start the manufacturing process but don’t end up being administered is simply that there aren’t enough starting cells to produce enough good, transfected T cells,” said He.
It’s not that much in vivo versus ex vivo, it’s more like having the right technology for the right therapy.
—Natalia Elizalde, VIVEbiotech
Therefore, improving cell collection and selection could have a significant impact downstream. Bracco is developing a buoyancy-based cell selection technology designed to isolate specific cell populations more gently than conventional magnetic approaches. “Because the process is gentler, we can preserve more healthy cells for the next stage of manufacturing,” explained He.
The technology uses microbubbles that attach to specific cells, causing them to float to the surface, where they can be collected. The microbubbles can be designed to recognize different cell surface markers, allowing the technology to select different cell types, and even harvest different cells sequentially.
Innovative technologies like this help manufacturers make the most of what each patient can provide, preserving more viable cells at the outset and giving developers greater control over the material that moves through the rest of the process.
And the toolkit is only continuing to expand. As in vivo approaches mature alongside improvements in ex vivo manufacturing, developers will only gain more options for how and where therapeutic cells can be generated, engineered, and controlled — both outside and inside the body.
A growing cell therapy toolbox
VIVEbiotech works across both ex vivo and in vivo programs, and Elizalde has seen technologies developed for one approach begin to influence the other. “One of the benefits of working across both areas is seeing how innovations developed for one application could also be applied for the other,” she said.
Advances in areas such as vector targeting, biodistribution, purity, and characterization in in vivo systems could ultimately improve ex vivo manufacturing and vector performance. At the same time, decades of experience with ex vivo therapies in process development, quality control, and large-scale manufacturing are helping to inform the emerging in vivo field.
In other words, the technologies may be different, but the problems they are trying to solve do overlap. Both approaches need to deliver the right cells, to the right place, at the right time, with enough control to produce a safe and effective therapy.
In the end, these technologies are complementary rather than competitive. Some patients and diseases will benefit from the precision of engineering cells outside the body, while others could benefit from the speed, scalability, and potentially broader accessibility of generating them inside it.
For now, the excitement around in vivo CAR T is less a sign that ex vivo has reached the end of its road than a sign that the field has more ways to approach the same fundamental challenge: getting therapeutic cells to the patient safely, effectively, and at a scale that makes cell therapy accessible to more people.
