行业分析：所审阅的 FDA 完整回复函中约 75% 涉及 CMC 关切，CGT 制造能力成共性主题

By Sidharth Ananthanarayan, clinical research and quality professional

A common thread links many of the complete response letters (CRLs) that the FDA recently released, they illustrate how insufficient manufacturing capabilities can hobble even the most promising scientific advances, such as cell and gene therapies (CGTs). Whether a drug or biological product works or fails often comes down to engineering, execution, and rigorous quality standards.

The challenges begin at the very first step, when the starting materials are derived from human donations. These materials must be processed and then used in manufacturing activities. For example, blood or bone marrow donations for certain CGTs require a complex logistical setup that must be rigorously tested to withstand any logistical challenges and ensure timely delivery for further processing. Furthermore, rigorous aseptic manufacturing requirements and patient-specific chains of custody add to the complexity, creating a reality where strict controls and compliance are essential to prevent errors and ensure patients receive the treatments that could save their lives.

To characterize the thread, I downloaded and analyzed the openFDA CRL dataset to identify the records that reflect issues related to chemistry, manufacturing, and controls (CMC).¹ I reviewed all 426 complete response letters, and since there is no active categorization of CMC-related decisions, I used keyword search methodology seeking CMC-related concerns. Based on my analysis, about 75% of the CRLs flagged some form of CMC-related concerns. Although this is an estimate, the direction helps to understand the gaps in the CMC data presented to the agency as part of submissions.

The CRL Trend Analysis Shows The Following Recurring CMC Themes

• Inspection readiness: In a few CRLs, the agency highlighted unresolved CMC issues identified during pre-license inspection, which impacted the submission.
• Data/documentation completeness: The agency informed the biotech companies that their submissions did not consist of all the necessary data or documentation related to change controls and other unresolved issues from pre-license inspection.
• Manufacturing process control: The agency questioned certain manufacturing process controls related to donor screening, testing, and eligibility requirements followed for CGT manufacturing; these questions further stressed the impact on the final product quality.
• Process validation and sterility: The agency emphasized on concerns about a sterility test method’s process validation and sterility testing procedures.
• Release testing: In one instance, the agency expressed concerns about the proposed assay and its applicability for validating the process used for release testing.
• Stability and specifications: In certain CRLs, the agency also highlighted concerns about the product stability and specifications provided in the submissions.

Across products, many submissions struggle because the evidence package cannot extensively support that the product can be made, controlled, tested, released, and inspected with confidence. Each CRL and its underlying case study is unique, but it outlines the multidimensional risk of manufacturing CGT products due to its complexity of manufacturing and logistics. A product’s viability can be challenged by inspectional observations, an immature potency assay, incomplete donor documentation, sterility method gaps, insufficient change-control evidence, or an underdeveloped comparability strategy. The recurring problem must be addressed as early as possible, and companies must demonstrate control across the product lifecycle.

So, What Does Better CMC Readiness Look Like For CGTs?

The solution is not to wait until the BLA submission process is initiated but to document and assemble a compliance story proactively. CGT sponsors need a life cycle CMC strategy that matures as the product goes through manufacturing and clinical trials.^2,3,4

First

Define the controls as early as possible to identify critical attributes, process parameters, donor material sourcing, in-process controls, validation, release testing, stability attributes, and product attributes. The definition should evolve to accommodate the additional requirements as the product reaches the final stages of submissions.

Second

Ensure all the validation, sterility, and comparability mechanisms used or planned to be used have a clear development and validation path. The respective partners and vendors in consideration for these activities should also have appropriate mechanisms in place to ensure compliance with the regulatory standards. Common pitfalls, such as contamination controls, sample volumes, method suitability, and process changes, should be addressed with robust and disciplined processes.

Third

Have a 21 CFR-compliant and validated digital trail of the chain-of-identity, batch records, donor eligibility records, manufacturing records, testing equipment records, shipping records, and any other clinical information pertaining to the product. The information should be accessible, dated, and have appropriate audit trails, backups, and periodic reviews to ensure the records are consistent and tell the complete story of the CGT product.

Fourth

Inculcate a continuous inspection readiness discipline. This is a challenge but plays an important role if implemented early in the development process. Any observations while becoming inspection ready should be addressed with appropriate quality procedures and corrective and preventive actions with effectiveness; these steps would ensure the gaps in the process are addressed and tested before the submission.

Fifth

Be adaptable and ready to tailor the contents based on the regulatory agency’s requirements. If the product is being submitted for authorization in different regions, the contents must be tailored and submitted based on the evolving requirements of the agencies. The adaptability ensures that all the appropriate data are included in the order required by the reviewing authority and ensures readiness to share more details if requested.

In the end, the CGT products require both innovation and manufacturing discipline with regulatory flexibility to help patients with high unmet medical need. The CRL trends highlight that manufacturing problems are not secondary to the science; they are often the reason the science cannot yet be delivered. For CGT, the major risks are variable starting material, immature potency assays, sterility and microbiological method gaps, limited comparability evidence, inspection readiness problems, and fragmented data systems.

The solution is to build CMC readiness as part of development, not as a submission rescue effort. Define the control strategy, mature the assays, and validate the systems. Document the process to prove comparability and ensure audit trails for all the activities performed. Connect every critical manufacturing decision to patient safety and product quality and show that corrective actions work. In CGTs, manufacturing is the journey from biological possibility to clinical reality.

References:

1. U.S. Food and Drug Administration. (n.d.). Complete response letters. openFDA. Retrieved May 25, 2026,  from https://open.fda.gov/apis/transparency/completeresponseletters/
2. FDA, Flexible Requirements for Cell and Gene Therapies to Advance Innovation:
3. FDA, Considerations for the Development of Chimeric Antigen Receptor (CAR) T Cell Products, January 2024: https://www.fda.gov/regulatory-information/search-fda-guidance-documents/considerations-development-chimeric-antigen-receptor-car-t-cell-products
4. HHS/FDA, Potency Assurance for Cellular and Gene Therapy Products, December 2023: https://www.hhs.gov/guidance/document/potency-assurance-cellular-and-gene-therapy-products

About The Author:

Sidharth Ananthanarayan is a clinical research and quality professional with a doctoral degree in business administration. He has contributed to multiple clinical development programs, supporting cell therapy products for oncology, autoimmune, and neurological indications, and has worked in operations, computer system validation, regulatory compliance, AI quality strategy, and cross-functional collaboration in regulated environments. Sidharth has also contributed to initiatives focused on improving operational processes and supporting quality-driven decision making throughout the clinical research lifecycle. In addition, he engages with the professional community through networking, knowledge sharing, and research-related activities.