A number of gene therapies are in late-stage clinical trials and expected to reach the market in the next several years. Unlike traditional biologic drugs, gene therapy production can involve the manipulation of replication of viruses. Segregation of manufacturing operations involving viruses is a crucial consideration when designing processes and overall facilities.

Significant Market Potential

While the current market for gene therapies is small, with just seven drugs approved to date (four in China, two in Europe and one in the US), there are at least 12 additional candidates that have reached late-stage clinical trials, leading to expectations for significant growth in the coming years.1 Many large bio/pharmaceutical companies and a number of emerging and medium-sized biotech firms are developing gene therapies as treatments for cancer; hemophilia; neurological, ocular and cardiovascular diseases; and many other disorders that often have no existing cure or require repeated treatment with existing drugs. Roots Analysis identified 483 gene therapy molecules in the marketed and clinical pipelines in 2015.1

From January 2013 to April 2014, US companies raised $600 million to support their gene therapy development programs.1 Novartis recently received FDA approval for chimeric antigen receptor T (CAR-T) cell therapy Kymriah™, for the treatment of patients with B-cell precursor acute lymphoblastic leukemia (ALL). Kymriah, which uses a patient’s own T cells to fight cancer, is the first FDA-approved therapy based on gene transfer. FDA is expected to approve the second gene therapy for the US market in 2018, with the most likely candidate being Spark Therapeutics’ Luxterna, a treatment for Leber Congenital Amaurosis, a genetic eye disorder that leaves sufferers legally blind by the age of 21, which was granted priority review by FDA in late August 2017.2 A decision from the agency is expected in mid-January. Overall, Roots Analysis predicts the global gene therapy market to grow by 48.9% annually to reach a value of $11 billion by 2025.1

Minimizing Cross-Contamination Risk

Manufacturing processes that involve the replication of a virus present several challenges with respect to facility design and equipment selection. Virus particles are on the nanometer scale and can pass through standard 0.2 micron “sterile barrier” filters used in typical process systems. As a result, there is a higher risk of them being spread throughout areas in which they are used, thus presenting a potential risk for environmental contamination. This carries impacts for process operations and operator health and safety. Virus particles from one process could potentially cross-
contaminate other processes completed in a multiproduct facility. More controls are therefore required to segregate and contain these process streams from other parts of the manufacturing plant.

The biggest differentiating concern for production facilities using viruses is the risk of cross-contamination.

Environmental Segregation

The biggest differentiating concern for production facilities using viruses is the risk of cross-contamination. For any single product facility, it is necessary to prevent contamination of process steps by adventitious agents. For multiproduction facilities manufacturing two or more different gene therapy vectors, it is essential to prevent helper virus particles or the product vector from one process contaminating the other. In both cases, the processes must be environmentally segregated from the remainder of the facility. 

The Importance of Process Mapping

To create an appropriate design for a gene therapy manufacturing facility that provides the necessary level of environmental segregation, the design engineers must be familiar with all the specific process operations that will be performed. Constructing a process map for all of the intended processes in the facility from an operational perspective can be a key tool for communicating process requirements. Specific requirements for each process — equipment, material flows, personnel movements, etc. — must be considered. The level of desired operational flexibility within the facility should also be factored. A process equipment closure analysis — whether the process steps used with the selected equipment are performed open to the environment, briefly exposed, closed or functionally closed — should be performed and documented as part of the facility basis of design. The choice of stainless steel, disposable or hybrid systems may factor into these considerations. Understanding of requirements and regulatory guidance will determine which processes can be performed side by side in the same room, and which must be conducted in segregated areas of the facility. Space requirements will impact the environmental air handling schemes such as room classification and HVAC planning.

For most closed pharmaceutical processes (when the process is completely contained and separated from the production environment), introduction or removal of gases and fluids are through system boundary filtration. While these filters are typically sized to capture most environmental contaminants such as bacteria and particulates, viral particles (typically 20-100 nm) can pass through. Their diminutive size makes viral particles especially difficult to contain when producing and processing in large quantities. Therefore, the steps within a manufacturing process that involve the use of viruses are generally segregated completely from other process areas within the same facility. Similarly, it is important to map out the movement of all materials containing, or that may have come into contact with, virus particles. GMP flow diagrams depicting the movement of materials, people, equipment, waste and product are critical in challenging the design and ensuring that contamination and cross-contamination risks are understood and suitably mitigated. HVAC diagrams depicting air handler zoning, room classifications and room pressurization must also be reviewed to ensure that air systems do not transport contamination from one area to another.

Preparation, Production and Purification

Manufacturing of gene therapies involves many different process steps and operations, including weighing and dispensing of raw materials (including powders and liquids), solution formulation, growing and infecting host cells, and numerous downstream purification steps. 

Weigh and dispense activities are typically handled in a separate room. Media powders are by design growth promoting, and present a higher risk of containing contaminating viruses. Dust containment exhaust systems or closed powder addition systems are used to enable containment of raw materials during open handling. If raw materials are weighed and dispensed into functionally closed powder addition systems, solution formulation can be performed in the same space as the process that is being prepared for. However, it may nonetheless be desirable from an operations standpoint to group all solution preparation into a central segregated solution preparation suite.

Cell-culture initiation and expansion operations prior to infection can be conducted just as cell-culture processes for the production of monoclonal antibodies (mAbs) and therapeutic proteins. The industry has accepted that the functionally closed upstream production trains for therapeutic proteins, but not viral operations, can be deployed using an open ballroom approach. The ballroom approach features a large open operational space where closed processing equipment can be co-located in the same space. Examples include mAb seed trains and production bioreactors operating side by side. To mitigate the risks of cross-contamination, all of these activities should be segregated from steps that involve the use of viruses.

Processes involving host cell infection, viral production, purification and product formulation should be spatially segregated in a separate room in order to contain vector particles within a specified zone in the facility. For HVAC, these spaces should utilize dedicated air handling units or single pass air flow to minimize contamination risks. Here, too, as long as each process is performed in a functionally closed equipment train, the process steps may be conducted in the same room. For multiproduct facilities, processing of multiple gene vectors should be performed either on a temporally segregated campaign basis (with sanitization between) or in parallel but in completely segregated viral production spaces for each product campaign produced.

Vector drug product filling is a low-volume, low-speed operation, and is typically performed using isolator filling systems. As with other filling operations, these have higher room classification requirements and their own dedicated spaces. Unlike mAbs or therapeutic proteins, however, these filling systems must be decontaminated to inactivate any residual vector presence within the filling isolator prior to equipment opening and changeover.

Stainless, Disposable and Hybrid Equipment Solutions

Selection of the equipment used for gene therapy manufacturing can have a significant impact on the level of effort and cost required to segregate production steps from the surrounding environment. The pharmaceutical equipment industry has well-developed solutions for the production of mAbs and other therapeutic proteins, and similar solutions are used for these steps within the overall gene therapy manufacturing process. There are stainless steel or disposable equipment solutions available and well-
developed methods for selecting the best options based on specific process and throughput requirements.

For the viral vector processing steps, because it is necessary to demonstrate complete removal of all virus particles between campaigns, single-use systems are attractive. These come pre-sterilized and eliminate the need for cleaning and cleaning validation, thus reducing the risk of cross-contamination, while also reducing downtime and cleaning costs. The use of disposable technologies may significantly simplify the overall production facility due to reductions (or eliminations) of utility systems and simplification of automation. Construction, validation and start-up of facilities utilizing disposable equipment are typically much faster and less expensive than their stainless steel counterparts. Complete disposable pre-sterilized systems may also be easier to close for processing, which in turn can enable for lower room classifications that require less extensive mechanical equipment (e.g., airlocks, air handling systems) and can lead to smaller production spaces and lower facility costs. Even so, the performance of a cost analysis is recommended to confirm that disposable technologies are advantageous. The cost of goods with these systems can be highly impacted by run rates and other factors, and in some cases, hybrid solutions using both stainless steel and disposable systems may be more appropriate.

Bespoke Design Is The Best Solution 

Given the challenges associated with gene therapy vector manufacturing, at CRB we take a client-focused approach to facility design, drilling down through each process to consider all relevant factors. One of our goals is to reduce the need for equipment movement and the number of necessary rooms, and thus the production-area footprint, while still providing appropriate safety and environmental controls, logical flows of materials and personnel, and better equipment usability for operators. This bespoke design process allows for greater facility flexibility while ensuring efficient production processes and operator safety. 


  1. Gene Therapy Market, 2015 – 2025. Roots Analysis. Feb. 2015. Web.
  2. Lovell, Ethan “Opinion: How investors should play gene-therapy Stocks,” Marketwatch.com. 6 Sept. 2017. Web.