August 16, 2022
1: Can you give us an overview of the step-by-step gene therapy manufacturing process?
The manufacturing of gene therapy products is complex and time-consuming, entailing many sequential steps from the time a production process is started to the testing and release of the gene therapy material. At Myrtelle, to make our gene therapies we utilize a type of cell-based production system called the HEK293 Transient Transfection manufacturing process, and this is the process by which the majority of rAAV gene therapy medicines are manufactured with today. This is a biological manufacturing process whereby living cells and genetic material called plasmids are used to produce the intended gene therapy medicine. To describe the manufacturing process, let’s use the analogy of building a house. In this case, the living cells are our tradespeople. They’re efficient, and can create many different and complex things, however they need instructions to create the specific house we want. This is where the use of plasmids in our manufacturing process comes in. Plasmids are the blueprints for the house, and they tell the cells exactly what medicine we want to make. Once the house is finished being built, there’s usually some trash leftover, the landscaping is a mess, and you need a clean-up crew and landscapers to come in and make the house look pretty. This is where the purification part of the manufacturing process takes over, cleaning up and removing anything the cells made which is not our medicine, and nicely packaging the medicine for use. Finally, we need to have the house inspected to ensure that it is safe to move into. The home inspector is equivalent to the release testing we do on our medicine, ensuring that the medicine is safe for use prior to administration.
2: Can you explain cGMP and why that is important?
The term cGMP (or GMP) stands for “current Good Manufacturing Practices” and is a set of minimum standards which manufacturers of medicines must follow. For our house analogy, this would be equivalent to the building codes which builders must follow to ensure the house is properly and safely built. cGMP applies to all aspects of manufacturing and includes requirements for and use of rigorous documentation such as batch records and standard operating procedures (SOPS), appropriate quality raw materials, robust and proven operating procedures, detection and investigation of deviations which occur during the manufacturing process, reliable quality testing, and a strong quality management system which oversees it all (just to name a few). The “c” in cGMP, which stands for “current”, is then a reminder that these standards are always improving as we learn to do things better, and any manufacturer of medicines must stay up to date with the latest practices. Adherence to cGMP is then enforced by regulatory agencies throughout the world, such as FDA in the US or EMA in the EU, through inspections of the manufacturing facilities and as part of the regulatory clinical trial submission and licensure process.
cGMP is a critical component of a multi-tiered system which ensures safety and quality so that the medical product performs as intended. Use of and adherence to cGMP is important as it ensures when a patient receives treatment with a medicine that has met a minimum requirement for safety and quality. Adherence to cGMP also certifies that whatever information is written on the vial or in documents about that medicine is true and correctly reflects what is actually inside the vial and will be administered to the patient. Like the house, we can’t actually see what’s behind the walls of a room, but adherence to building codes gives us confidence that the house was built correctly and is safe to live in.
3: How long can the manufacturing process take and what are some of the hurdles?
Manufacturing of gene therapy products is complex and laborious, with a huge amount of detail. The manufacturing process itself, from thawing a vial of cells to having a vial of medicine in hand, can range from 2-3 months depending on the scale of manufacturing. The testing of the medicine once manufactured to release it for use can typically take another 3-4 months. If you also need to manufacture the plasmid starting materials, this would add an additional 6 months to the front end. So overall, to make and release a single batch of medicine could be a 6 to 12-month long process. Like building a house, this is not something you can order online and have shipped out to your home the next day.
One of the biggest hurdles right now is manufacturing capacity. The field of gene therapy has grown exponentially over the past decade, and there is a high degree of specialization and technical know-how needed to manufacture these medicines. It also takes a number of years to build, demo and get approval to run a new cGMP manufacturing plant. As such, there’s a large number of companies vying for the same, currently limited manufacturing capacity. We’re also an emerging field, literally defining the cutting edge of gene therapy every time we produce a batch. There is no one-size-fits-all roadmap we can follow; we’re literally creating it for each new gene therapy as we move forward. Because of this, there’s also a lot of development and training we need to do with our manufacturing and testing partners to ensure we’re reproducibly producing the highest quality of medicine we can. This then adds additional time and effort to get our medicine to patients.
While these are significant hurdles which Myrtelle, and the gene therapy field as a whole, are dealing with today, there’s a lot of smart and highly motivated people working on advancing the field. We are definitely on the path to better understanding these medicines and how to manufacture them faster and more efficiently, and I’m highly optimistic we’ll see that improvement in the coming years.
4: When a batch of gene therapy medicine is made, what determines the yield of that batch and why some batches yield more than others?
Prior to manufacturing the first batch of any gene therapy medicine we first need to develop the process, usually on the benchtop in a lab. As stated previously, we’re defining the cutting edge of gene therapy today with every batch we make, so this development process can take a large amount of time. The amount of time we spend on development must be balanced with the aspiration to get to the clinic and meet the needs of patients. In order to achieve this timing balance, it is common for early-stage clinical material to be first manufactured using a developed, but not necessarily fully optimized, manufacturing process. As we continue to produce additional batches, gain experience manufacturing at that scale, and further continue our process optimization efforts, we better understand the parameters that influence productivity, we optimize the many and various steps in the production process, and we can then better predict the yield each batch will produce while also reducing variability. Going back to the house building analogy, the first house or two a team builds will take longer and most likely require a bit of reworking here and there. However, by the time they’ve built 10+ houses of the same model, they’re experienced, highly efficient experts on how to build that particular house.
Regarding what determines the yield for each batch, there are two primary levers we can pull, those being scale (how big is the manufacturing and how many batches we produce) and productivity (how much medicine do the cells make and how much do we lose in the purification process). Scale is often the easier lever to pull, i.e. you simply make things bigger; however, we can only scale the manufacturing up so much, and as mentioned earlier manufacturing capacity in the field is limited so we can only produce so many batches each year. The cost associated with scaling up can also become prohibitive, both to the company and the patient. The productivity lever increases the amount of medicine we get out of each batch, and thus can reduce the needed scale of manufacturing. However, productivity increases take time to develop, and this development time must be weighed against delays to treating patients. Ultimately, it becomes a fine-tuned balance between manufacturing scale, productivity, and meeting the patient community need which determines the final batch yield.
5: How is the safety & quality of the gene therapy product controlled?
Safety for the patient and patient communities we are treating is of the utmost importance for those of us at Myrtelle and others in the field. Multiple pages would be needed to go over all we do to ensure safety and quality of our gene therapy products, however at a high level there are four major categories: 1) the quality of materials going in, 2) manufacturing under cGMP, 3) the purification process, and 4) release testing. All raw and starting materials which go into or are used in the manufacturing process are tightly controlled and thoroughly tested for safety and quality. The highest-grade materials are used, cell lines are controlled through use of master banks (from which all vials are identical and highly tested for safety) and plasmids are thoroughly tested prior to use (with new testing techniques being developed and added to the testing panel all the time to increase safety and quality). The purification process is specifically designed to remove contaminants and impurities which may be present or inadvertently enter the manufacturing process. This includes removal of adventitious agents (such as live pathogens or infectious viruses), cell line related impurities (such as host cell protein and DNA) and product related impurities (such as empty capsids), to name a few. A large panel of release tests is then conducted to ensure that the medicine is safe and of high enough quality for use, and if it is not, the batch is rejected and will not be used for treating patients. This is why it takes 3-4 months to conduct the release testing, as there are so many tests being run to ensure safety and quality prior to use. Finally, all manufacturing of our medicines is done under a cGMP environment, as mentioned earlier.
To go back to our house analogy, only the finest quality and certified materials are used to build the house (materials going in), our clean-up crew and landscapers are highly experienced and thoroughly trained (purification process), and all construction work is done with the necessary permitting and inspections completed prior to the move in date (release testing).