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

At NecstGen, scientists are focussing on bridging the gap between induced pluripotent stem cell (iPSC) research and clinical application. We spoke with Catalina Gomez-Puerto, Senior Scientist at NecstGen, about her journey in this field and the company’s strategic role in enabling iPSC-based innovations.

Catalina’s Background and Expertise

What inspired your interest in iPSCs, and what motivated your move to NecstGen?

I’m originally from Colombia, and when I started my undergraduate studies, Cellular Biology wasn’t offered as a standalone program. The main options were Medicine or Microbiology. I chose Microbiology because I was fascinated by how the human body responds to pathogens and wanted to explore that through research, rather than clinical practice.

Later, I received two scholarships to pursue a Master’s in Molecular and Cellular Life Sciences in the Netherlands. During my internship at the Hubrecht Institute, I worked with induced pluripotent stem cells (iPSCs) for the first time, and it was a turning point. The fact that these cells can become any cell type in the body is incredible! It opened my eyes to the possibilities of regenerative medicine.

During my PhD at UMC Utrecht, I focused on how hematopoietic and mesenchymal stromal cells maintain their stemness and avoid differentiating into mature cells like white blood cells or osteoblasts. That work deepened my interest in stem cell biology. For my postdoc, I wanted to move closer to clinical application, so I joined Leiden University Medical Center (LUMC) to study the molecular mechanisms behind Pulmonary Arterial Hypertension. Later, at Cambridge University, I returned to iPSCs, this time using them to model the disease in a patient-specific way.

Eventually, I moved into industry, where I focused on developing iPSC differentiation protocols, particularly for neurodegenerative applications. What really motivated my move to NecstGen was the opportunity to be one step closer to the patient. Here, I’m working on translating iPSC protocols into scalable, GMP-compliant processes for clinical manufacturing helping turn promising science into real therapies that can make a difference in people’s lives.

NecstGen’s Work with iPSCs

What makes NecstGen’s approach to iPSCs different? 

What sets NecstGen apart is that we are a mission driven, non-profit organisation focused entirely on enabling the field of Cell & Gene Therapy to move forward. Our mission is to make advanced therapies accessible, and that means working alongside both academic groups and industry partners to translate iPSC research into clinical reality.

Being wholly owned by Leiden University Medical Center gives us a unique position. LUMC brings extensive expertise in pluripotent stem cell research and ongoing iPSC-based clinical activities, and that knowledge base is directly connected to our work. It allows us to combine scientific depth with the infrastructure and mindset required for GMP manufacturing.

We are development-focused, not just production-focused. That means we invest time in helping our partners design robust processes, analytical methods, and strategies that are reliable and reproducible at clinical scale. Our team of experts is actively engaged in this journey, rather than simply providing a service.

Current iPSC Projects and Challenges

What kind of iPSC-related projects are you working on? 

We are supporting partners and clients with iPSC cell line generation, cell banking, process development, analytics, and GMP manufacturing.

For example, we are collaborating with Leiden University Medical Center (LUMC) on the RegMedXB U(iP)Scale project, which is part of the RegMed XB Diabetes Moonshot. The goal is to use iPSCs to develop regenerative therapies for Type 1 diabetes. Today, managing the disease means lifelong insulin administration using injections or pumps, along with constant glucose monitoring. iPSC-derived treatments could potentially restore the body’s ability to produce insulin, offering a real chance to cure the disease rather than just manage it.

In this project, NecstGen’s role is to demonstrate reliable scale up of stem cell-derived islets. Using bioreactors, we aim to facilitate scalable manufacturing. Technology transfer has been undertaken from LUMC into NecstGen’s process development laboratories, where our team is now collaborating with LUMC towards a cost-efficient, scalable manufacturing process.

What are the biggest challenges in iPSC differentiation, and how is NecstGen handling them? 

One of the main challenges is ensuring that iPSCs develop into the right cell type for a specific therapy. For example, treating Parkinson’s disease requires generating dopaminergic neurons. We focus on making differentiation methods clinically viable, safe, and consistent so they can be used in treatments.

To achieve this, we optimise protocols through systematic process development, using a Design of Experiments (DoE) approach to identify and fine-tune the key parameters that influence differentiation outcomes efficiently. These can include cell seeding density, media composition, timing and concentration of growth factors, oxygen levels, and the type of culture surface or microcarrier system used.

Differentiation is highly sensitive to small variations, which is why it requires skilled personnel. Interpreting cell morphology, adjusting protocols based on subtle shifts in behaviour, and troubleshooting unexpected outcomes all demand deep stem cell expertise. Our team has hands-on experience with both adherent and suspension cultures across a range of iPSC-derived lines. By combining this expertise with robust experimental design and a quality-by-design mindset, we help our clients move from research protocols to GMP-ready differentiation processes with confidence.

NecstGen’s Expertise and Capabilities

What should potential clients know about NecstGen’s iPSC expertise? 

At NecstGen we take a very different approach compared to many CDMOs that allows us to be truly collaborative and development oriented.

Within the Cell Therapy team, I work alongside Melissa van Pel, our Head of Cell Therapy, who sets the strategy and ensures that projects are designed with clinical translation in mind, and Óscar Bártulos, our Lead Scientist, who brings almost two decades of experience in pluripotent stem cells. Together, we integrate process development, analytical testing, and manufacturing expertise into a single, joined-up pathway.

My own focus is on process development for iPSC-derived therapies. That means helping partners design and optimise methods for iPSC expansion and differentiation—whether in adherent or suspension systems, with manual steps or in bioreactors. We make sure those protocols are robust, reproducible, and can be smoothly transferred into GMP cleanroom production.

Because we have purpose-built GMP cleanrooms, development labs, and in-house QC capabilities, we can support partners all the way from early-stage concepts through to GMP manufacturing. Our goal is always the same: to ensure the therapies developed with us are scientifically robust, technically feasible, and manufacturable under clinical conditions—ready to move into the clinic and, ultimately, to patients.

The Future of iPSC Therapies

Where do you see iPSC research heading, and what role will NecstGen play? 

IPSCs are incredibly versatile, they can be used not just for cell replacement therapies, but also for disease modelling, drug discovery, and personalised medicine. Starting from a single donor sample, we can generate a virtually unlimited supply of therapeutic cells, which could truly transform how we treat disease.

Of course, there are still challenges. There is a need for more consistent and reproducible differentiation methods across laboratories and scales. Transitioning to GMP manufacturing can introduce hurdles regarding cost and scalability. And before these therapies can become standard practice, safety, long-term engraftment, and regulatory approval need to be addressed.

One exciting direction is creating iPSC lines that are less likely to trigger an immune response. This could make off-the-shelf therapies possible, using the same cells to treat many patients. If it works, it could be a game-changer, making treatments more accessible and moving beyond the need for patient-specific approaches.

Working at NecstGen

What do you enjoy most about your work? 

Being part of a growing company means having the chance to shape processes and build something new. The team here is also very collaborative, everyone is working toward the same goal of making these therapies a reality.

Final Thoughts 

Catalina and the NecstGen team are focused on moving iPSC-based therapies closer to the clinic. By combining scientific expertise with clinical manufacturing, NecstGen supports the translation of iPSCs from research to therapies.

We explore the field of Cell Therapy with an expert from NecstGen, a Non-Profit Contract Development and Manufacturing Organisation (CDMO) for Cell and Gene Therapies. While examining the complex and innovative work that characterises the company’s activities, we also gain insights into what makes working at NecstGen an exceptional experience in cellular medicine. We spoke with Marten Visser, Cell Therapy Specialist, about his work at NecstGen.

Cell Therapy Specialist

Marten Visser joined the company two years ago and has played a significant role ever since. He has extensive experience in T-cell therapy development and manufacture to treat melanoma and ovarian carcinoma. He specialises in cleanroom operation and translational development to create treatments and deepen the field’s understanding.

“I have experience in all parts of the process, from isolating T-cells from patient material to final formulation all under GMP procedures. Because of my expertise, I can contribute to customer projects in many ways.” –  Marten Visser, Cell Therapy Specialist at NecstGen.

When Marten was ready for a new challenge, NecstGen crossed his path. From the beginning, Marten witnessed and contributed to the company’s growth in multiple ways. His role at NecstGen proved the ideal opportunity to apply his knowledge in a broader context. So, in addition to his work in the NecstGen development laboratories, he was also closely involved in setting-up general GMP procedures and processes.

“I felt I was ready for something new. I wanted to use the knowledge I have gained in my previous role, and when I saw the available position at NecstGen, there was a good match. At that time the cleanrooms were being constructed. There were cables and construction workers everywhere. When I started, they had just begun contouring the cleanrooms on the third floor. Everything had to be built from scratch, and I had the opportunity to actively contribute to this.” – Marten Visser, Cell Therapy Specialist at NecstGen.

A dynamic workday

A workday at NecstGen is dynamic and open. Being a smaller company there are diverse responsibilities offering scope for growth and development in new areas. For example, when the cleanrooms were still under construction, many workdays revolved around creating processes, procedures and the corresponding documentation. Customer projects are more prominent now, resulting in many days of conducting experiments and working hands-on in the laboratory. Of course, there is also plenty of time dedicated to data analysis, discussion, and learning. On some days, meetings take precedence over other routine tasks. The diverse functions at NecstGen offer many opportunities for growth and learning.

“At NecstGen everyone is aligned with our mission to translate research programs into life-saving treatments. As a company, we are flexible and have the expertise and the commitment to assist customers in translating their processes into GMP procedures and clinical production.” Marten Visser, Cell Therapy Specialist at NecstGen.

All in all, working as a Cell Therapy Specialist at NecstGen comes with many opportunities. Each day may be different, from working in the laboratories to writing GMP documentation. Close collaboration with colleagues and customers is crucial to their and NecstGen’s success. Working at NecstGen enables us to develop as professionals in many ways, all while making a difference to the world by contributing to novel Cell- and Gene Therapies.