Translating cell therapy processes into GMP is rarely derailed by one large mistake. It slows down through accumulated small ones.

About Melissa van Pel
Melissa van Pel is Head of Cell Therapy at NecstGen. She holds a PhD in immunology and haematology and spent roughly 22 years in academia, including leading a cell therapy manufacturing team producing clinical trial material. At NecstGen, she is responsible for cell therapy process development and clinical manufacturing.

When Processes Move, the Small Things Break First

When therapy developers come to NecstGen, they already have a process in place. Sometimes it is still very close to how it was run in the R&D lab; sometimes it is more established. In both cases, the transfer begins with documentation review, rewriting procedures to our format, and training our operators on the specific process. The most challenging part is rarely the headline steps.

“The devil is always in the details,” Melissa explains. The problem is not missing protocols, but missing habits. The small actions operators perform without thinking rarely make it into written procedures. Once a process changes hands, those gaps become visible. If that tacit knowledge is not transferred, running the process at another facility will not lead to the same results. GMP manufacturing depends on the ability to execute a robust production process through a procedure that is well described and well documented.

GMP Readiness Is More Than People Expect

One of the biggest surprises for developers entering a GMP environment is the volume of documentation and process control required to develop and execute a clinical production process. Many underestimate how much compliance actually demands.

“What we often see is that people tend to underestimate the work that GMP and working in a cleanroom puts on you,” Melissa notes. This gap often surfaces when developers feel their process is already GMP-ready. In practice, we frequently identify missing data, fragile steps, or materials that are not suitable for clinical use. A process must consistently produce a safe product that meets pre-defined specifications, not just work once under ideal conditions.

Knowing When to Stop Optimising

Many therapy developers struggle with a different problem: not when to start improving a process, but when to stop. Scientists are trained to keep refining yield, efficiency, and understanding, but that instinct can delay clinical translation.

“As a therapy developer, you know that a process can always be improved. Therefore, it’s very tempting to keep on further developing your process and never say: this is the process, this is where I stop, and now I’m going to bring it to the clinic.”

That decision needs to be made deliberately. When designing a process, you need to keep the end in mind and define what good enough looks like for that stage, including the right level of quality, consistency, and risk. Continuing to refine is valuable research, essential for understanding mechanisms of disease and mechanisms of action. But it is not the same as moving toward an actual therapy for patients.

Building Teams That Can Bridge Development and GMP

Building a team capable of spanning both worlds is itself a challenge. Early on, it was not always easy to find people with both deep GMP experience and strong development skills. Some came with long GMP backgrounds but limited exposure to development work. Others were strong scientists without cleanroom or regulatory experience.

By training teams in-house, NecstGen has built a group that can develop robust, consistent, and GMP-compliant manufacturing processes while understanding the practical demands of working in a cleanroom environment. “I do feel now we have a great team where we have both the subject matter expertise across a very broad range of cell therapies and processes, as well as the GMP knowledge,” Melissa says.

A Position Between Academia and Industry

NecstGen is fully owned by Leiden University Medical Center and operates on a mission-based, not-for-profit model. Working with academia, SMEs, and larger pharmaceutical companies, it sits naturally between those two worlds, inspected and functioning as industry, while remaining close enough to academic thinking to help developers adjust their expectations earlier.

“Given the people who work at NecstGen and their backgrounds and experience both in academia and industry, we can talk to both worlds.” That ability to translate between R&D and regulated manufacturing shapes how projects move forward.

“In the end, you need a production process that is predictable, robust, and reproducible, time after time.” — Melissa van Pel