Process development for cell-based products should begin in parallel with early R&D activities, once proof-of-concept data for the lead candidate is available (Figure 1). Initial efforts focus on process design and technology scouting to establish a foundational manufacturing process that supports preclinical development. This should also include an early evaluation of the GMP implementability of the process, covering the suitability of raw materials, the assessment of closed-system devices, and the design of critical manipulation steps to ensure they can be executed in a cleanroom environment.

Once a preliminary process is defined, comprehensive process characterization must be conducted to identify critical process parameters (CPPs) and critical material attributes (CMAs). During the transition to GMP manufacturing, manufacturing science and technology (MSAT) teams collaborate with process development teams to support key activities such as process optimization, technology transfer, troubleshooting, and final adaptations required for operating the process in a GMP-compliant environment.

Applying a Quality by Design (QbD) approach is essential in process and analytical development for cell-based products. Unlike conventional pharmaceuticals, cell therapies are highly process-dependent, and their safety and efficacy are intrinsically linked to the consistency of the manufacturing process. Due to the high complexity of living cells, it can be very challenging to establish how product quality is affected by the process. QbD provides a systematic framework to ensure quality is built into the product from the earliest stages of development, promoting better understanding, reduced variability, and robust control strategies.

Central to QbD is the generation of a quality target product profile (qTPP). The qTPP outlines the desired clinical attributes of the final product, including indications, dosage form, route of administration, and critical performance measures such as potency and safety. As outlined in the ICH Q8(R2) guideline, the qTPP is "a prospective summary of the quality characteristics of a drug product that ideally will be achieved to ensure the desired quality, taking into account safety and efficacy of the drug product”.

In the qTPP, critical quality attributes (CQAs) are defined. CQAs are the physical, chemical, biological, or microbiological properties of the product that must be controlled (through appropriate specifications) to ensure product quality and alignment with the qTPP. In cell-based therapies, CQAs may include cell identity, viability, purity, and potency. Early identification of CQAs typically involves literature reviews, expert input, prior knowledge, and early analytical studies.

Critical process parameters (CPPs) are process variables that have a direct impact on CQAs. Examples include culture temperature, media composition, or expansion time. These may be identified through designed experiments that correlate process parameters with product attributes. Similarly, critical material attributes (CMAs)—such as donor variability, raw material composition, and reagent quality—are identified through risk assessments and screening studies, as they can significantly influence CPPs and ultimately CQAs.

A risk-based approach, as advocated by ICH guidelines such as ICH Q8(R2), Q9, and Q10, underpins the QbD framework. ICH Q8(R2) outlines the principles of pharmaceutical development using QbD, Q9 focuses on quality risk management, and Q10 describes a model for a pharmaceutical quality system. Together, they guide developers in using science- and risk-based decision-making to focus efforts on where they matter most.

Early-phase process development for cell-based therapies involves a structured, stepwise approach to ensure that the product and process are suitable for clinical translation and future scalability. This approach includes:

1. Process design and scouting
   Development begins with process and analytical design, supported by technology scouting to identify GMP-compliant equipment and raw materials of appropriate quality. A key objective is to establish a GMP-compatible processing approach that minimizes contamination risk and is feasible for manual or semi-automated execution. Raw materials, such as growth media and reagents, must be sourced from suppliers with appropriate documentation and traceability. Initial feasibility studies confirm the suitability and reproducibility of the setup. This should also include support processes like medium preparation. In parallel, a scalability strategy—whether via scale-up or scale-out—should be outlined to support post-Phase 1 development, even if not immediately implemented.
2. Process characterization
   Once the baseline process is defined, systematic characterization studies are conducted to identify critical process parameters (CPPs) and critical material attributes (CMAs), determine their acceptable ranges, and assess the stability of intermediates during hold times. This involves systematic studies—such as risk assessments and designed experiments—that evaluate the impact of process and material variables on product quality. Applying Quality by Design (QbD) principles from the start ensures a science- and risk-based understanding of the process, enabling robust and reproducible manufacturing. These activities include confirmation studies to ensure consistency and reproducibility under defined conditions. 
3. Technology transfer
   The optimized process is then transferred to a GMP manufacturing environment, ensuring alignment with facility capabilities and regulatory requirements.
4. Scaling for future trials
   As clinical development progresses, the pre-defined scale-up or scale-out strategy is implemented. Notably, demonstrating comparability between manufacturing processes is particularly challenging for cell-based products due to their inherent variability and sensitivity, making early process standardization and control critical.

By generating an effective process and analytical feedback loop, the risk of failure should decrease as therapies progress towards GMP manufacturing. This reduced risk is achieved through several factors, such as the careful evaluation of robustness, the development of an effective control strategy, and the choice of suitable equipment for scale-up/scale-out. The feedback loop also allows for scaling down to each previous step as needed, to further improve the process and optimize the design. This continuous optimization of the process and analytical methods creates a robust and adaptable manufacturing process, de-risking and accelerating the development of innovative cell and gene therapies.

When developing cell and gene therapies, several manufacturing challenges are faced, including product variability, complex process control, raw material and reagent quality, and scalability. Below, we explain how each of these challenges arises, and how they can be mitigated through effective process and analytical development.

1. Product variability
   Cell-based products are composed of living cells, which inherently exhibit biological variability. This variability may stem from donor-to-donor differences (especially in autologous therapies), intrinsic heterogeneity of the cell population, or sensitivity to environmental conditions such as cytokine concentrations, oxygen tension, or shear stress during processing. These factors can affect critical quality attributes (CQAs) such as potency, identity, and purity.
   To manage this variability, it is essential to implement a standardized and well-characterized manufacturing process as early as possible during development. Applying Quality by Design (QbD) principles facilitates the development of robust control strategies and reduces the risk of out-of-specification batches during clinical and commercial production. 
2. Complex process control
   The manufacturing workflow for cell-based therapies typically includes multiple complex steps (e.g. cell enrichment, expansion, differentiation, formulation, and cryopreservation), each of which must be tightly controlled to maintain cell integrity and functionality. Many of these steps are still performed manually or with minimal automation, increasing the risk of operator error and contamination. Moving toward closed, automated, and scalable systems can substantially improve process control and consistency. However, implementing these technologies requires significant early investment and technical validation. Early alignment of the process design with available automation platforms and facility capabilities is key to long-term success. In addition, robust in-process analytics are necessary to monitor CQAs in real time and adjust process parameters when needed.
3. Raw material and reagent quality
   Many raw materials used in cell therapy manufacturing (e.g. human serum, cytokines, and growth factors) are biologically derived and can vary from lot to lot. Furthermore, GMP-grade or fully characterized versions of these materials may not be available. Raw materials must be critically assessed early in process development for their suitability under GMP conditions, with attention to source, quality certification, viral safety, and consistency of supply. Whenever possible, developers should use materials intended for future clinical manufacturing during development studies to ensure that material-related variability is properly captured and understood. Establishing strong supplier relationships and qualification processes is also crucial to ensure consistent raw material performance over time.
4. Scalability
   Scaling a cell therapy process from research laboratory to clinical or commercial production is inherently difficult. Unlike small molecules or biologics, the product is often sensitive to minor changes in processing conditions, equipment, or environment. Scale-up (increasing batch size) can affect critical process parameters (CPPs) such as nutrient gradients and oxygen levels, potentially altering cell behavior. Scale-out (replicating smaller batches in parallel) may offer a lower-risk approach, especially for autologous products, but comes with increased operational complexity.

As described, process and analytical development are key components of the cell and gene therapy product lifecycle. However, for early-stage developers, the challenge lies in translating these principles into practice. Here are our top recommendations for implementing effective process and analytical development strategies, to ensure a streamlined and de-risked route to market:

• Starting with the end in mind – When developing the process for a cell or gene therapy, clinical and commercial goals should be in mind from the start. This forward-thinking strategy ensures that quality, scalability, GMP compliance, and cost-effectiveness are built into every stage of the process, accelerating the transition to GMP manufacturing and beyond.
• Adopting a QbD approach – Incorporating QbD principles into process development aids in predicting and addressing potential weaknesses. This ensures consistent product quality and GMP compliance, while providing the appropriate level of flexibility to foster innovation and continuous improvement.
• Supply chain design – As many cell and gene therapy components are highly specialized, raw material reliability, quality, and availability should be prioritized. To ensure a long-term supply of key reagents, developing strong relationships with suppliers and designing a risk-controlled supply chain early in development is essential. This will ultimately facilitate scalable and cost-effective manufacturing, preventing any potential delays and batch failures.
• Early engagement with regulatory authorities – Engaging with regulatory authorities early in the development process provides invaluable guidance, ensuring the proper evolution and harmonization of the regulatory framework. This proactive approach helps streamline the approval process and address potential regulatory challenges early on, paving the way for successful manufacturing and commercialization.
• Effective cross-departmental communication – There are several departments involved in cell and gene therapy development, including process development, quality control, quality assurance, manufacturing, and regulatory affairs. Regular communication between these departments is essential for ensuring alignment across all functions. Having a dedicated team of project managers can help facilitate this coordination and optimize all aspects of the process, ultimately leading to more effective and efficient production.

To develop ground-breaking cell and gene therapies, a strategic approach to process and analytical development is needed. This requires the consideration of several components, including the integration of QbD and continuous feedback, supply chain security, cross-departmental collaboration, and regulatory compliance. Partnering with an expert in cell therapy development and manufacturing, such as Evotec, can greatly assist with this.

Evotec is shaping the future of cell therapies with its broad therapeutic expertise, combined with industry-leading capabilities for iPSC-based, autologous, allogeneic, and donor-derived therapies. We provide a one-stop solution for cell therapies, streamlining and simplifying the journey from early R&D through to IND submission, clinical development, and GMP manufacturing.

When partnering with Evotec, developers can count on us for comprehensive regulatory support, avant-garde technologies, flexible and scalable equipment, and state-of-the-art cleanroom facilities. Our combined expertise and capabilities allow early-stage developers to streamline and standardize the process, while ensuring GMP compliance, sterility, and cost-effectiveness from the beginning. With this comprehensive support, our partners are accelerating the development of life-changing cell therapies.