A "Particular" Problem For Cell Therapy Products, Part 1: Extrinsic And Intrinsic Particles

By Andreas M. Beckhaus and Drew N. Kelner, ProDeMaCon LLC Consulting

As most cell therapy products are administered intravenously, they need to comply with the compendial requirements for particulate matter. USP<1>¹ requires that each final container shall be inspected to the extent possible for the presence of observable foreign and particulate matter and that the limits for subvisible particulate matter set forth in USP <788>² are met. In a recently published FDA-483 follow-up letter,³ the agency cited Novartis for the sampling plan and test procedure for Kymriah’s primary container cryobags that “are not appropriate to assure that cryobags are “free of…particulate matter” as required by your acceptance criteria”.

Particulate matter in cell therapy products can be generated from a variety of sources within the manufacturing and production processes, as with traditional biotech and pharmaceutical manufacturing. But what is particular about cell therapy products?

1. The cell therapy drug product consists of “particles” itself, namely cells, making its appearance cloudy such that it is very difficult to detect visible particles.
2. It is practically impossible to routinely determine subvisible particles with compendial methods in the presence of cells.
3. There is no final filtration step as with most other drugs for parenteral administration.

Background

Particulates in pharmaceutical products are either classified as visible or subvisible particles. Visible particles are defined as those visible to the human eye and are typically greater than about 100 μm, whereas subvisible particles are smaller and separated into two groups (&GT10 μm and &GT25 µm). Particles can be of three different origins: inherent, intrinsic, or extrinsic:⁴

• Intrinsic types are related to the manufacturing, formulation, packaging or assembly processes (e.g., glass, plastic, rubber, fibers from filters, etc.).
• Extrinsic types are foreign and unexpected, not part of the immediate manufacturing process (e.g., hair, non-process related fibers, paint, etc.).
• Inherent types are expected from the drug product itself and may — within limits — represent a generally accepted characteristic of the product (e.g., cell clumps, protein aggregates, etc.).

Part 1 of our publication focuses on intrinsic and extrinsic particles; inherent particles will be covered in part 2.

The USP states on its website:⁵ “With current manufacturing capabilities, it is not possible to manufacture injectable drug products that are completely free of particulates. Thus, minimizing their presence during the manufacturing process is a critical step in reducing their presence in the final drug product, which is a critical factor for the healthcare professional, the manufacturer, and the regulator — and ultimately, the patient”. Therefore, cell therapy manufacturers need to understand the potential origin and type of particles that may be present in their final drug product (FDP) as well as the potential process capabilities to reduce particles. A respective FDP control strategy needs to be put in place.

Safety Assessment

The medical literature is sparse with respect to case reports and experimental studies providing data to support the safety risk of particles (intrinsic or extrinsic) in humans.⁶ The medical assessment needs to consider that the patient populations that may be most at risk of particulate matter-related sequelae include patients with existing tissue damage, critically ill patients, and neonates.⁷ Particles can present both physiological and immunological risks to product safety; the physiological risks of intrinsic and extrinsic particles will be covered here, and the immunological risks specific to inherent particles will be discussed in part 2.

Depending on their size and origin, particles in intravenously administered products can impede and even block blood flow. Such particulates can become trapped in the pulmonary capillaries within the lungs, the diameter of which is approximately 12 μm to 15 μm, resulting in inflammation that can over time lead to vessel occlusion, thromboembolism, and other cardiovascular damage. The quality control requirements for particulates in pharmaceuticals and biopharmaceuticals are designed to reduce the likelihood of such damage. There is in principle no significant difference in the physiological behavior of intrinsic and extrinsic noncellular particulates between (bio)pharmaceutical drugs and cell therapies and, therefore, the regulatory requirements for these types of particulates in cell therapy drug products should in concept be comparable to those for pharmaceuticals and protein drug products.

Recommended Risk Mitigation Steps

The most conservative approach for a cell therapy manufacturer would be rejecting all containers with any visible particles and in addition testing all raw materials with direct or indirect cell contact for both visible and subvisible particles. However, that is not feasible in practice. For example, one individual batch of an autologous products often covers only a single dose and rejecting an FDP container could mean that the patient will not receive their urgently needed drug administration. A detailed risk/benefit assessment that considers the potential consequences of discarding the dose is needed in such cases.

As required in USP<1>¹ 100% control of each FDP container must be performed following the procedure outlined in USP<790>.⁸ Operators should be appropriately trained to identify intrinsic and extrinsic particles based on a proper defect library. This library should include representative examples of intrinsic particle materials such as glass, stainless steel, rubber (from stoppers), gasket material, fibers (e.g., from filters), plastic polymers (e.g., from single-use consumables), and proteinaceous aggregates. The library should also include representative examples of extrinsic particle materials such as hair, extrinsic fibers, paint, etc.

Performing a compendial visual inspection is not easy in light of the typically turbid appearance of a cell therapy product formulation. This limitation highlights the need for additional and frequent in-process controls for visible particles — covering the product stream, single use plastics, and other raw materials prior to use.

Furthermore, it is basically impossible to routinely test FDP samples for subvisible particles with methods described in USP<788>² due to the inherent presence of cells that are in the same size range as small subvisible particles. Thus, it is recommended to use alternative methods such as flow imaging microscopy for the characterization of subvisible particle contaminations in cell-based products (see below).

For some products, it may be advisable to consider a revision to the typical bedside patient administration by providing an IV administration set with each FDP vial that includes an appropriately sized in-line filter (e.g., 50 µm or 100 µm mesh size); such a filter has the potential to eliminate visible particles prior to administration. Prior to introduction of such in-line filters, different filters should be studied with FDP vials containing cell clumps to examine if the administration line could be clogged by cell clumps. To our knowledge, Carvykti is the only licensed cell therapy product using an in-line non-leukocyte depleting filter.

Recommended Studies

The importance of a solid, phase-appropriate raw material qualification program for all raw materials with direct or indirect cell contact is often overlooked. Every batch of raw material used in formulation and fill/finish, such as excipients, primary containers, bags for formulated drug product, and filling equipment with drug product contact, should be tested for visible and subvisible particles as part of the release process. After appropriate material qualification, this can be done by the material manufacturer or as part of incoming testing and release.

In order to finalize the testing and release strategy for other raw materials used in earlier process phases, it is essential to understand actual process capabilities and perform particle characterization studies. Such process capability studies could be done by running the full-scale process in the absence of cells (“sham runs”) and characterizing the results with respect to particle load at various stages. Data can be obtained on the potential particulate contribution of the raw materials and the process capability of clearing these in the wash and supernatant removal steps. The data obtained can be used to develop a science-based particle control strategy for all raw materials used in GMP production (excipients, reagents, single-use plastics, and other process aids) upstream or downstream of the potential clearance steps.

We typically recommend that these cell-free sham runs be conducted using the process and equipment that is representative of GMP production conditions, for example, as follows:

1. a “process run” that includes all excipients, reagents, single use plastics, and other process consumables,
2. a “water run” with particulate-free water, all single-use plastics, and other process aids in the absence of any excipients and reagents, and
3. a “spiked run” with particulate-free water, all single-use plastics, and other process aids without any excipients and reagents but spiked with commercially available particle standards at predefined process stages.

All particles found in the sham runs should be isolated and analyzed in order to assign their origin to specific materials or at least certain types of materials wherever possible. For subvisible particle load characterization, a flow imaging microscopy study⁹ with various FDP samples can be helpful for a process assessment related to minimizing potential particulate contamination and support the overall particle control strategy.

Conclusions

Cell therapy manufacturers need to develop a sound particulate control strategy as soon as they move into clinical trials. This is of high importance for patient safety and is becoming more of a focus for regulatory authorities. In addition, raw materials used in the manufacture of ATMPs need to be of the highest quality, especially, but not limited to, the presence of particulates, and need to be controlled in line with current regulatory guidance and specifications. Manufacturers should establish a comprehensive, phase-appropriate raw material program and consider the studies outlined in this article.

References:

1. USP<1> Injections
2. USP<788> Visible Particulates in Injections
3. https://www.fda.gov/media/174213/download
4. Clarke D, Stanton J, Powers D, Karnieli O, Nahum S, Abraham E, et al. Managing particulates in cell therapy: Guidance for best practice. Cytotherapy 2016;18:1063–76
5. https://qualitymatters.usp.org/controlling-particulate-matter-injectable-drug-products
6. Bukofzer S, Ayres J, Chavez A, Devera M, Miller J, Ross D, Shabushnig J, Vargo S, Watson H, Watson R. Industry Perspective on the Medical Risk of Visible Particles in Injectable Drug Products. PDA J Pharm Sci and Tech January 2015, 69 (1) 123-139.
7. Langille SE. Particulate Matter in Injectable Drug Products. PDA J Pharm Sci and Tech 2013, 67 186-200.
8. USP<790> Visible Particulates in Injections
9. Cui L, Kinnunen, K, Boltze J, Nystedt, J and Jolkkonen, J. Clumping and Viability of Bone Marrow Derived Mesenchymal Stromal Cells under Different Preparation Procedures: A Flow Cytometry-Based In Vitro Study. Stem Cells Int. 2016: 1764938.

About The Authors:

Andreas M. Beckhaus, Ph.D., is the president of ProDeMaCon LLC. He started his international career in the regulatory affairs department of Bayer Healthcare and in the following 17 years worked in several different functions (project management, life cycle management, portfolio management, and marketing) with increasing responsibility, focusing on biotech products and rare diseases. He further broadened his scope into medical devices at KCI Inc., a global wound-healing company. In 2014, Beckhaus started ProDeMaCon as an independent consulting business. Over the last several years, he worked with several clients in the CGT space (small and large pharmaceutical companies and CDMOs), with a focus on raw material qualification and particulate control strategies. He has a background in pharmacy and a Ph.D. in toxicology.

Drew N. Kelner, Ph.D., is president of Shenandoah Biotechnology Consulting, LLC and a principal consultant at ProDeMaCon LLC. In a 37-year career in the biotechnology industry, he has participated in the development of monoclonal antibodies and other biopharmaceutical products from both bacterial and mammalian cell sources as well as oncolytic viruses and CAR-T therapies. He retired from Amgen in 2015 from his position as executive director of global analytical Sciences. Kelner is the author of Taming Cancer: 21^st Century Biology and the Future of Cancer Medicine. With a background in protein biochemistry and molecular immunology, he received a B.S. in chemistry from Haverford College and a Ph.D. in biochemistry from Duke University.