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Technical Review Article | Open Access | Published 2 July 2026
Adapting a Monoclonal Antibody (mAb) Facility for Gene Therapy Production
Alfred Penfold | EJPPS | 312 (2026) https://doi.org/10.37521/ejpps31206
Introduction
Biopharmaceutical manufacturers are increasingly challenged to support a rapidly expanding therapeutic landscape where monoclonal antibodies (mAbs), viral vector gene therapies, and other advanced modalities must be produced with agility, regulatory compliance, and cost efficiency. Traditionally, manufacturers have built dedicated facilities for each modality due to differences in biosafety classification, process flow, contamination risks, and cleanroom requirements. However, this approach is no longer sustainable in a climate of increased development activities and economic pressure.
A detailed feasibility study was undertaken to examine whether an existing GMP compliant mAb Drug Substance facility could be successfully adapted for the manufacture of viral vector based gene therapies. The study considered technical, regulatory, biosafety, operational, and risk elements, and included engagement with the U.S. FDA to review the containment strategy, process flows, and facility layout.
The core finding is that mAb and gene therapy processes exhibit strikingly similar equipment, operational stages, and facility needs, allowing for significant reuse of existing infrastructure. The primary challenge, and the main differentiator, is the requirement for BSL 2, or BSL 2 Large Scale (LS), containment for gene therapy production, along with additional procedural controls and enhanced biosafety waste streams.
Upgrades, including targeted HVAC modifications, the installation of isolator technology for helper virus handling, improvements to waste treatment processes, and the implementation of comprehensive single use systems, were evaluated and found both feasible and efficient.
Ultimately, the feasibility study demonstrates that dual modality manufacturing of mAbs and gene therapy vectors within the same facility is indeed viable, compliant, and operationally efficient, provided that a comprehensive risk based, engineering led approach is applied.
Objective of Feasibility Study
Over the last decade, gene therapies have shifted from experimental pipelines to approved commercial reality. As more vector based therapeutics progress through clinical development, manufacturers are under pressure to expand capacity quickly while maintaining compliance with regulatory expectations and biosafety controls.
Many organizations have aging but functional mAb manufacturing facilities that could provide an immediate platform for gene therapy production if suitable modifications are identified and implemented. The global manufacturing landscape has made clear that retrofit and adaptation strategies are often faster, more cost effective, and more flexible than new builds.
The purpose of the feasibility study was threefold. Firstly, determine whether an existing GMP mAb Drug Substance facility can support the production of viral vector gene therapies. Secondly, identify the specific modifications needed to achieve compliance with NIH/BMBL BSL 2 and BSL 2 LS requirements. And thirdly, evaluate the facility, processes, biosafety strategy, and risk control measures in consultation with regulators.
Unlike many theoretical analyses, this study is grounded in real facility architecture, existing process flow paths, and operational practices. It covers upstream cell culture, downstream purification, biosafety considerations, risk mitigation, and operator requirements.
The overarching objective was to enable campaign based production of both mAbs and gene therapies without requiring physical reconfiguration between production runs, fully leveraging modern single use technologies to minimize risk and maximize efficiency
Overview of the Existing mAb Production Facility
The existing mAb facility evaluated in the study included the following core areas:
Inoculation and cell expansion rooms
Cell culture suites
Pre-viral filtration purification suites
Post-viral filtration purification suites
Wash room and autoclave
Waste treatment operations
Solution preparation areas
Freezing and storage facilities
The production facility, as illustrated in Diagram 1, contains rooms that were either CNC or with an area classification of Grade D or Grade C. The facility was constructed with an efficient layout and optimal flow in mind.
3.1 Centralized Solution Preparation
A central solution preparation suite can distribute media and buffers to any part of the production network, regardless of whether the destination is cell culture, pre-viral purification, or post-viral purification. This flexibility is crucial for multi-modality manufacturing.
3.2 Separation Between Pre-Viral and Post-Viral Purification Spaces
The physical separation and therefore segregation of pre and post viral purification is an architectural feature sometimes viewed as excessive for mAbs, but for gene therapy it becomes an asset by supporting the necessary containment philosophy and alignment with viral vector risk management.
3.3 Exclusive Use of Single Use, Product Contacting Surfaces
The product path is entirely single-use as follows:
Single use bioreactors
Disposable purification flow paths
Single use filtration assemblies
Pre-sterilized components and tubing sets
This design choice is arguably the single most enabling feature for the facility adaptation. It eliminates:
CIP/SIP system recovery time
Cleaning validation complexity
Cleaning agent residues
Shared equipment contamination risk
It also simplifies and accelerates the changeover time between mAb and gene therapy campaigns.
Process Comparison Between mAbs and Gene Therapy
One of the foundational elements of the feasibility study was a thorough comparison of the upstream and downstream processes for both modalities. The analysis confirmed that although gene therapy requires enhanced biological containment and introduces helper virus operations, the unit operations, equipment families, and process flow pattern are remarkably similar.
4.1 Upstream Processing Comparison
4.1.1 Cell Banking and Thawing
Both processes start with:
Frozen vial storage
Controlled thaw
Expansion in shake flasks and small bioreactors
4.1.2 N-1 Bioreactor Stage
For mAbs:
Typical N-1 bioreactor volume: 200 L
For gene therapy:
Perfusion-based N-1 bioreactor at 250 L
Both require:
Single use bioreactors
Closed sampling systems
Controlled temperature and agitation profiles
4.1.3 Production Bioreactor
mAbs:
2,000 L production bioreactor
Gene therapy:
Also 2,000 L, but includes a helper virus infection, which triggers BSL 2 containment needs. The similarity in scale and physical equipment requirements was a key finding.
4.2 Downstream Processing Comparison
4.2.1 Harvest and Clarification
Both processes use:
Depth filtration
Clarification systems
TFF-based volume reduction
4.2.2 Chromatography
Differences include:
mAbs:
Protein A
Viral inactivation
Polishing steps (AEX, CEX)
Gene therapy:
Membrane adsorber chromatography
Affinity purification steps optimized for viral vectors
Viral filtration (high retention)
Despite differences in resin selection or membrane characteristics, the equipment used is often identical.
4.2.3 Drug Substance Formulation and Storage
Both processes end with:
Filtration
Drug Substance freezing
Storage at low temperatures (for example, -70°C)
The remarkably similar workflows provide strong justification for shared facility operations.
The need for dedicated equipment was limited to the LN2 Cryovessels and Drug Substance Freezers (-70°C). The Isolator was also dedicated but unique to the gene therapy process when handling the helper virus.
Key Findings From Process Comparison
The feasibility study identified several foundational insights. For example, there is a strong alignment in scale and process flow. Most upstream and downstream steps use similar bioreactors, filtration systems, and chromatography architectures. The main challenge is regarding the need to comply with the BSL 2 and BSL 2 LS requirements when introducing the gene therapy.
The introduction of a gene therapy into the production facility requires enhanced biosafety measures to accommodate the helper virus and a higher viral risk classification. The additional requirements impact the HVAC strategy, existing pressure cascades, waste handling and operator protection.
5.1 Single Use Technology is a Major Risk Mitigation Advantage
The facility’s design ensures all product-contacting surfaces are single use, providing benefits such as:
Reduced cross contamination risk
Faster changeover
Minimized cleaning validation
Simplified procedural controls
Risk Framework: Viral and Microbial Classification
It is helpful to develop a risk profile for different modalities to establish some key segregation principles. The risk profile should also be based on regulations, industry best practices, and the company’s own risk profile and practices. The two separate risk profiles typically developed are for chemical potency and toxicity risk, and biological (viral and microbial) risk1. For the mAb and gene therapy operation the biological (viral and microbial) risk is more relevant when considering the risk profile.
In both cases, the category of risk ranges from low to very high. Each risk profile category contains a definition with examples. Profiles can also form the basis for the proposed segregation principles in the feasibility study. ‘Very high’ risk profiles align with clear regulatory expectations for dedicated manufacturing facilities.
A science and risk-based approach from first principles is recommended to assess the biological risk. QRM tools commonly used in the biopharma industry should provide good guidance on what is acceptable and were indeed used when conducting the feasibility study. Table 1 captures the types of modalities that relate more specifically to viral and microbial organisms with respect to risk profile, and provides an approximate risk ranking of viral and microbial risks. It can be used as an initial guide until the actual level of risk is determined by a more comprehensive risk assessment. A site biosafety committee will be required to help categorize the risk grouping of hazardous organisms
Table 1 – Viral / Microbial Risk Profile
Viral and microbial products have been classified into the following broad categories (excluding very high risks that are not in scope): low, medium, and high risk. Low risk includes mAb processes where characterized murine cell banks are used, BSL-1 bioprocesses, and fill finish of traditional therapeutic proteins. These are low-risk processes because the presence of viral material is low and if it is present, it is likely to be of animal origin and are not known to propagate in humans.
Medium-risk processes include those that use viral vectors, human cell lines where an adventitious human virus will replicate, or animal tissue that may have viruses but those that are not known to propagate in humans.
High-risk processes are typically those where human viruses may be present. These include human-donated material and culturing of live human viruses.
The Gene therapy processes fall under medium risk, reflecting the use of BSL 2 organisms, a higher likelihood of viral propagation and associated regulatory guidance. Some steps, particularly above the 10 L threshold, must follow BSL 2 LS regulations.
The medium risk classification for a gene therapy guides the decision making when considering the facility zoning, PPE requirements, level of Engineering controls and the waste treatment strategies.
Biosafety Requirements and Facility Modifications
The existing mAb facility required targeted upgrades to support gene therapy safely and compliantly. In summary, and guided by the requirement to meet either BSL 2 or BSL 2 LS, they included:
A closed processing philosophy
Biosafety cabinets for all open manipulations
Negative pressure environments (BSL-2 & BSL-2 LS zoning)
Dedicated AHUs for segregated zones
Enhanced decontamination systems
Isolator technology for helper virus handling
Validated heat treatment for liquid waste
Controlled removal of solid waste
The HVAC modifications needed for the gene therapy operation required the introduction of ‘sink’ airlocks to enable the level of containment needed when complying with BSL-2 and BLS-2 LS. Air handlers needed to be fully segregated and were facilitated by the existing HVAC zoning. For example, having separate pre and post viral suites with their own HVAC units.
The gene therapy liquid waste requires a validated thermal inactivation before discharge, and the solid waste requires enhanced PPE and bagging procedures with temporal segregation such as dedicated removal times when there is no production.
Facility Upgrade Plan
The existing mAbs facility needed to be upgraded to accommodate a ‘medium risk’ viral vector based product manufacturing process designed to allow the processing of biohazardous materials, as defined by the NIH/BMBL containment guidelines. The proposed upgrade is illustrated in Diagram 2.
The modified facility therefore needed to accommodate BSL-2 engineering containment measures wherever viable organisms are present. Due to the scale of the operation sometimes exceeding the 10L threshold, BSL-2 LS (Large Scale) needed to be applied at scales over 10L.
The Biosafety Philosophy was based on closed processing with open handling operations limited to small scales that would be conducted within a Biosafety cabinet; with one noticeable exception being the ‘helper’ virus which would be handled in an Isolator in the Cell Culture room.
The BSL-2 zones were designed to operate at a negative pressure in relation to the surrounding areas. The HVAC design needed to employ dedicated air handlers for the respective segregated product zones.
Finally, all biologically contaminated solid waste would need to be collected for decontamination, and all biologically contaminated liquid waste would need to be decontaminated by a validated heat treatment system before discharge to the site waste.
The study detailed how each room would need to be modified by either further Engineering controls, by enhanced procedural controls, or a combination of both. In summary, Table 2 below highlights the final BSL-2 and BSL-2 LS designated zones.
Table 2 – Biosafety Area Classifications for the Gene Therapy
Production Area | BSL-2 Zone |
Inoculation & Cell Expansion | BSL-2 (<10L) |
Cell Culture | BSL-2 Large Scale (>10L) |
Pre-Viral Filtration | BSL-2 Large Scale (>10L) |
Post-Viral Filtration | BSL-2 Large Scale (>10L) |
Wash Room | BSL-2 (<10L) |
Waste Treatment | BSL-2 Large Scale (>10L) |
These modifications were minimal relative to a full facility rebuild.
Risk Mitigation Measures
An early-stage FMEA risk assessment was conducted to highlight potential high-level risks and was focused on the impact of having two different product modalities within the same facility.
It was identified that additional procedural controls are inevitable when manufacturing a Gene Therapy, but these have been minimized by the introduction of various facility modifications and engineering controls to reduce the risk of cross-contamination.
The majority of risks were mitigated by the single use nature of the facility, i.e. all wetted / product contact parts were single use preventing the need for cleaning validation of the single use elements.
The single corridor increases the risk of cross-contamination for viral vector manufacturing and would need to be managed closely with temporal segregation controls to minimize the risk. The Biowaste System would also need to be upgraded to BSL-2.
The existing drainage could not be used for viral vector production and an “above ground” solution for collecting waste would need to be designed and then risk assessed. For example, the existing drainage did not have double-walled pipework to meet the BSL-2 requirements in the event of a leak.
In summary, the main risks were identified as follows:
Single corridor increasing movement based contamination risk
Incompatibility of the existing drainage for viral waste
Helper virus handling risks
Potential cross contamination between campaigns
Operator exposure risks
The mitigation strategies were developed as follows:
Temporal segregation between product types
Above ground waste collection systems
Isolator for helper virus steps
Enhanced gowning (coveralls, overshoes, Tyvek sleeves)
Dedicated waste streams
Closed single use product paths
Gowning Philosophy
Driven by the BSL-2 requirements, operators would be required to don an additional disposable coverall, gloves and overshoes in the entrance vestibules when entering either the Grade D Cell Culture Room, or Grade D Purification Room. A set of Tyvek sleeves would also be required when working in a Biosafety cabinet. The additional gowning provisions for BSL-2 areas ensures both product protection and operator safety.
FDA Engagement
Due to the risk of supplying clinical and launch material for both mAbs and viral vectors from the same facility, a Type B meeting was requested with the FDA to review the proposed plans. The gene therapy under evaluation had received RMAT status by the FDA (Regenerative Medicine Advanced Therapy2), and the reason for holding a Typer B meeting rather than a more typical Type C meeting. The gene therapy approval was being accelerated by the FDA in part because it was addressing an unmet medical need.
The FDA thought the proposed plan “appeared acceptable” based on the floor plan, equipment layout, room classifications, containment features and use of single-use technology.
However, the FDA did request that the Isolator handling the helper virus is VHP decontaminated.
The bidirectional personnel and waste flow was not considered ideal, and the FDA agreed that there was a need for temporal segregation, waste decontamination and dedicated equipment where single use might not be possible.
In summary, the feedback from the FDA Type B meeting was as follows:
• Facility layout and flow strategies ‘appeared acceptable’
• Use of single use technology was viewed favorably
• Temporal segregation was necessary and appropriate
• The helper virus isolator must undergo full VHP decontamination
• Dedicated equipment is required where single use is not feasible
The feedback helped validate the design and risk mitigation approach.
Conclusion
The feasibility study demonstrates that with focused engineering modifications, a robust biosafety strategy, and strong reliance on single use technologies, a mAb Drug Substance facility can be successfully adapted to support viral vector gene therapy manufacturing.
Key outcomes:
mAb and gene therapy unit operations can align closely
Single use systems minimize contamination risk
BSL 2 and BSL 2 LS requirements are achievable within the existing mAb facility footprint
Operator and environmental safety can be maintained
Regulatory bodies view the approach as acceptable when well justified
Campaign-based dual modality production can be practical and efficient
This adaptive strategy provides manufacturers with a faster, more economical pathway to support the growing pipeline of gene therapy products without the need for extensive new construction. Retrofitting a gene therapy operation for a mAb product would have been a lot simpler with the BSL-2 requirements already captured in the design of the facility.
The feasibility study did not progress any further but may have continued had there not been an alternative gene therapy facility subsequently acquired by the company.
References
1. “Accommodating Multiple Modalities in the Same Facility”, by Tom Bannon and Alf Penfold, ISPE Pharmaceutical Engineering, November-December, 2022. https://ispe.org/pharmaceutical-engineering/november-december-2022/accommodating-multiple-modalities-same-facility.
2. US Food and Drug Administration. “Regenerative Medicine Advanced Therapy Designation.” Published November, 2025. https://www.fda.gov/vaccines-blood-biologics/cellular-gene-therapy-products/regenerative-medicine-advanced-therapy-designation.
Author Information
Author:
Alfred Penfold, Technical Director - GMP / Regulatory Compliance
PM Group
Alfred Penfold has more than 35 years of experience in the pharmaceutical and biotechnology industry working for GSK, Catalent, Pfizer and PM Group. At Pfizer, he held multiple positions, including Engineering Lead for all manufacturing operations in the US and Canada. Alf has held similar roles in Latin America, Europe, and Asia. He was later responsible for all serialization deployments within Pfizer and has advised the FDA on serialization. Alf now works for PM Group as their Technical Director for GMP / Regulatory Compliance and has performed GMP design reviews, quality risk assessments and prepared agency review meetings, such as FDA Type C meetings, for clients in Europe, the US, and Asia. He is a member of the ISPE Regulatory Quality Harmonisation Committee’s EMEA Regional Focus Group’s steering committee, a member of the ISPE Europe Leadership Team and an elected member of the PHSS Management Committee.
Corresponding Author: alfred.penfold@pmgroup-global.com
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