Safety and urgency

Cell and gene therapies (CGTs) are a class of therapeutic that is fundamentally different from traditional biopharmaceuticals. This is because they involve living cells and this makes them inherently more complex than simple chemical entities or recombinant proteins. Cells interact with their environment in ways that can be difficult to predict and control, so ensuring treatments are safe as well as effective can be a minefield. The cells that form the basis of CGTs must be strictly consistent in terms of their identity, potency and safety. Quality control must be stringent and uncompromising, yet must also be performed with urgency, as patients needing these therapies do not have time to waste. “Another important point to consider is the fact that CGTs are often produced in small batches, and each batch is unique in that it is related to one patient and is unique in terms of the starting materials,” remarks Félix Montero-Julian, healthcare scientific director at bioMérieux, a leader in the field of in vitro diagnostics.

The use of cell therapies comprising modified cells that are given to patients by infusion is growing fast, particularly autologous cell therapy (ACT), in which an individual's cells are cultured and expanded outside the body. CAR T, for example, is a highly complex and innovative immunotherapy that involves collecting and using the patients’ immune cells to create a chimeric antigen receptor (CAR) that can bind to specific proteins on cancer cells.

Large numbers of CAR T cells are grown in the laboratory and can be used to treat certain blood cancers, though studies are assessing their efficacy in the treatment of other types of cancer. Products currently on the market include Yescarta for treating two types of non-Hodgkin lymphoma, and Tecratus, which is a CAR T-cell therapy for the treatment of relapsed or refractory mantle cell lymphoma (MCL). Also advancing rapidly is gene therapy delivered using a viral vector as a drug to insert a gene into a group of cells. In this technique, a recombinant adeno-associated virus (rAAV) enables the insertion, deletion or substitution of DNA sequences into the genomes of live mammalian cells. Gene therapy product Kymrhia, for example, is a genetically modified autologous T cell immunotherapy delivered by viral vector and made from a patient’s own white blood cells before it’s used to treat relapsed or refractory follicular lymphoma. In the case of autologous therapies, the starting material is unique, which makes it challenging to establish a manufacturing process and some adjustments are needed to ensure that the final product meets the required quality control specifications for safety and efficacy. “Because they involve the manipulation of genetic material, it is extremely important to detect and monitor potential changes,” says Montero- Julian. “For example, in the case of CAR T cells, the vector copy number (VCN) – a measurement of the transgene copies within a CAR T cell product – is a product-specific characteristic and must be quantified prior to patient administration.” High VCN increases the risk of insertional mutagenesis – a phenomenon which can itself cause malignant cell transformation – which makes transgene integration in the drug product an important safety parameter to measure for CAR T-cell release. “CGTs also require specialised storage and handling conditions to preserve their stability and potency,” adds Montero-Julian. “Thus, quality control is more challenging, and the manufacturing process must be carefully monitored and controlled.”

Recognising risk factors

The development and delivery of CGTs bring their own unique risk profiles. With cell therapy, there is risk along the entire vein-to-vein journey, from when cells are taken from the patient, through the modification process and then in the phase where they are reintroduced to the body. Risks at every stage can be lowered as much as possible, but the process needs to be done fast, as these therapies are often made to order for patients in urgent need of treatment, and for whom other conventional treatments have failed. Time is of the essence in cell therapies, but speed must be balanced with quality control and safety. “Reducing manufacturing and lot disposition times is not as critical for viral vectorbased gene therapy manufacturing,” notes Mike Brewer, director of regulatory at Thermo Fisher Scientific. “Unlike cell-based therapies, where time to deliver the drug to the patient is critical, for an rAAV, the overarching concern in manufacturing is to create a high quality, high purity product.

“The challenge for a cell therapy is that the process is the product, especially if we are talking about ACT, so there is a smaller set of quality control release tests.” For both types of therapy, testing and safety protocols must be rigorous in order ensure compliance with regulatory standards and deliver a working therapy as quickly and efficiently as possible. These protocols must, however, address many challenges. As cell therapy products are manufactured at low volume and all of the product must be kept for the patient, analytical methods must be applicable to minimal volumes of sample to provide results. New analytical techniques are required to ensure accurate characterisation and to monitor the product’s consistency throughout its life cycle. “The short-shelf life of these products means traditional compendial analytical methods used in quality control testing may not be sufficient to fully characterise the complex nature of cell and gene therapies, or are not adapted at all to provide results faster,” says Montero-Julian. “Typically, sterility testing takes 14 days, but the use of new rapid microbiological methods has allowed us to release products in just seven days.”

The complexity of the raw materials involved makes the quality control more challenging, and as they are uniquely tied to one single patient, it is essential to ensure full traceability of the entire process and have the right IT and digital systems in place to guarantee data integrity for each batch. “Also, because one donor is one batch, the analytical methods used for the quality control should allow the scalability of the process and respond to the patient demands in terms of volume, throughput and automation,” Montero- Julian explains. “The manufacture of cell and gene therapies involves the use of living cells in culture with media, and these products are prone to contamination if they are not handled appropriately. So, it is important to implement measures to avoid contamination.”

Compliance, contamination and quality control

Regulatory standards tend to be conservative, though they are constantly developing to reflect the challenges of this innovative field of research. There are rigorous standards for sterility testing, and it is widely recognised that the current growth-based sterility test described in the United States Pharmacopeia (USP) and European Pharmacopoeia with an incubation period of at least 14 days is not suitable for products with a short shelf life such as CGTs.

To accelerate the testing and release of CGTs, the European Pharmacopoeia has published a new chapter on microbiological examination of cell-based preparations, and the USP is working on a similar approach to allow manufacturers to use automated growth-based methods that are more suitable for the release of cell therapy products after just seven days of incubation. Mycoplasma testing is a mandatory part of quality control for CGTs, as bacteria can contaminate cell cultures and impact the safety and efficacy of the final product. It can be performed using cell culture-based methods, which are extremely arduous, require high levels of technical expertise and need 28 days to get a result. “This is absolutely not compatible with the product-release schedule of a CGT,” says Montero-Julian.

“Alternatively, the indicator cell culture approach requires elevated technical expertise and even then it takes five to eight days, but the limit of detection of mycoplasma with this technique is extremely high. The nucleic acid testing is also considered an alternative method, but again requires high-level expertise and a specialised lab.” So far, the only two methods that can reach regulators’ sensitivity expectations are culture-based, which are too slow for cell therapies, or PCR methods, notes Brewer. “Other methods are limited on sensitivity and specificity,” he adds.

Risks in the manufacturing process can be addressed by automation, which delivers an improvement in consistency and a reduction in the risk of potential error, as multi-step manual processes tend to introduce the risk of deviation and inefficiency. The quality control process, however, remains challenging in terms of speed because of the nature of testing for mycoplasma and adventitious virus – which includes bacteria, fungi, viruses and other contaminants that can be inadvertently introduced into biological systems. “There is no rapid test for adventitious virus available yet,” says Brewer. “There are technologies with potential, but they are currently in the exploratory stage. Nevertheless, methods are being introduced to validate the sterility tests, and regulators understand the urgency to get patients infused. People have been trying to develop a sterility test that can be done in hours, but it is challenging with microorganisms, as the length of time they require to grow means validation by regulators is difficult.” As it stands, the emphasis in quality control is on rigour and risk reduction. It may be a long time before the process can be made significantly quicker, but patient safety and outcomes must always take precedence.