Optimizing Starting Material Quality for Cellular Therapeutics

When a company strives to make an excellent product, they start with the highest quality materials. Cell therapy is unique in that the building blocks for the “product” are living human cells; since each donor is unique, variability is inevitable. But variable or low-quality starting material complicates the manufacturing process by introducing a need for complex separation strategies or repeated manufacturing runs, leading to higher costs and resource requirements. Choosing optimal apheresis instrumentation and collection methods is one of the most important steps in ensuring high-quality starting material and giving cellular therapy products their best start.

“The quality of your precursor material to the overall development process is absolutely critical. Raw materials are everything, and I think the smart companies know that.” Dr. Fred Miesowicz, former COO, Argos Therapeutics

Optimized apheresis collection starts with the donor, and access to a reliable donor pool is a must. A large, diverse, and well-organized pool of recallable donors means there will be a stronger chance of finding just the right donor or donors within a satisfactory time frame.¹ But more than that is needed to guarantee superior quality starting material. The newly thriving clinical cell therapy market is leading to a greater demand for apheresis driven technologies. Cellular therapy most commonly focuses on the use of primary cells, stem cells, and various types of immune cells as the basis for treating a wide range of diseases, including cancer, autoimmune disease, and inflammatory disease.^2,3 Ensuring high-quality starting material means focusing on both optimizing therapeutic cell yield and maintaining peak therapeutic potency.

Choosing the Optimal Apheresis Machinery

The cells that form the basis of these treatments can be derived from different sources; cord blood, bone marrow, and peripheral blood are all used, and each tissue source has its pros and cons. Both cord blood and bone marrow contain a higher percentage of stem cells than peripheral blood, but bone marrow collection requires a surgical procedure that is uncomfortable to the patient, and with cord blood, there is no possibility of a repeat donation. Peripheral blood, in contrast, is an easily accessible source that is often preferred because collection is relatively easy on the patient and repeat donation is, therefore, more common. Though stem cell counts in peripheral blood are relatively low, yield can be significantly increased through mobilization techniques, during which the cells are stimulated to leave the bone marrow and enter the general circulation.

This is where apheresis comes in. Apheresis is done for a variety of reasons, both for blood component collection and as a therapy in and of itself. Different blood components are collected to treat different pathologies. For example, plasma is needed to treat severe liver disease or hemophilia, while platelets are often needed to treat leukemia patients. Manufacturing a cell therapy most often requires the collection of peripheral blood mononuclear cells, or PBMCs. These cells include stem cells, lineage-committed progenitor cells, and different types of immune cells that will form the basis of a given therapeutic.⁴ 

The downstream application for the cellular therapeutic dictates the instrumentation and methodologies that are optimal for a particular manufacturing pathway. For example, the practice of using peripheral blood mononuclear cells (PBMCs) as cell therapy starting material relies on a specialized type of apheresis known as leukapheresis, in which white blood cells are separated out from other blood components through centrifugal separation.

Leukapheresis systems are available with different capabilities,⁵ so the specific type of system a clinic uses will depend on a number of considerations, such as preferred flow rate and volume capacity, process flexibility, software capabilities, and the monetary resources of the clinic. Pediatric leukapheresis collection has unique requirements that differ from adult leukapheresis collection. Collecting sufficient volume is a challenge; line sizes are smaller, and collection times may need to be shorter, among other considerations. There may also be medication or mobilization strategy restrictions.

Aside from such patient-related considerations, there are monetary considerations. Leukapheresis instrument manufacturers are increasingly incorporating automated technology into the machine’s capability for online separation, to help minimize downstream handling. On the one hand, automation has the advantage of letting the operator carefully control collection volumes, track inventory and patient data, and minimize sample handling. On the other hand, automated instruments are generally costlier, and may require specially trained and experienced operators. Not all clinics or pharmaceutical manufacturers can afford the most complex equipment or data platforms.

Since different variables can play into the quality and quantity of cells that can be collected, standardization of both leukapheresis instrumentation and operator training across cell therapy starting material collection sites is important. In a best-case scenario, apheresis nurses will be highly trained and experienced, with excellent venipuncture skills and a good bedside manner to put donors at ease. Optimizing and standardizing equipment and training helps protect and enable the highest quality, consistency and potency of the downstream clinical product.

Cell Collection Methods Impact Therapeutic Quality

Collection methods also affect product consistency. The goal of any cell therapy collection method is to optimize the number of healthy therapeutic cells present in the starting material. This often means that collection protocols must reach an optimal balance of yield and purity.⁶ During the leukapheresis procedure, slower flow rates may result in lower yield volume, while faster flow rates can stress and damage cells, or result in poor quality separation of the targeted blood components. Various enrichment techniques may be incorporated into the collection protocol itself, so specific methods should be worked out in advance to obtain optimal results. During post-collection processing, the number of target cells in a particular leukapheresis unit will inevitably decrease with each step in the manufacturing process, as cells are lost to handling methods and environmental stress. Quality control criteria for leukapheresis units should set pre-determined values for acceptable collection volumes, cell counts, purity, and cell viability.

“The sector needs to better define cell identity, potency and purity, so that the active pharmaceutical ingredient becomes the majority of the fraction injected. The tools and technology already exist, we just need to develop more thoughtful and standardized characterization assays to ensure a potent product. That’s one of the concerns we have right now, and one of the things everyone is working on to address.” Dr Robert Tressler, VP of Laboratories for the San Diego Blood Bank

Tight coordination of cell collection sites and processing labs is required to preserve the viability and functionality of therapeutic cell types. Once the leukapheresis unit is collected, the therapeutic potency of the cells must be protected until the unit can reach the processing facility. In practical terms, this often means leukapheresis products are cryopreserved prior to their use. Cryopreservation can improve stability while reducing or alleviating highly coordinated logistics challenges. Robust, data validated cryopreservation methods and media will optimize cell viability and functionality. Quality control assays should be performed both prior to shipping and upon arrival to ensure that product integrity has been maintained.

Apheresis derived starting material will increasingly impact the practice of medicine, as cell-based therapies are validated and approved for the clinic. Using best practices when determining instrumentation and collection methods will ensure that these important therapies are given their best start. 

References

1. Juliano L, et al. The Importance of Collection, Processing and Biopreservation Best Practices in Determining CAR-T Starting Material Quality. Cell and Gene Therapy Insights. 327-336. 2018.
2. Forman SJ, and Nakamura R. Hematopoietic Cell Transplantation. Cancer Network. Nov 2015. http://www.cancernetwork.com/cancer-management/hematopoietic-cell-transplantation 
3. Hamers L. How to make CAR-T cell therapies for cancer safer and more effective. Science News. June 2018.
4. Wang X, and Riviere I. Clinical manufacturing of CAR T cells: foundation of a promising therapy. Molecular Therapy: Oncolytics; 3. 2016.
5. Kim J, et al. Comparison of Spectra Optia and COBE Spectra apheresis systems' performances for red blood cell exchange procedures. Transfusion and Apheresis Science. 55 (3) 368-370. December 2016.
6. Physicians Plasma Alliance. A Guide to Leukapheresis: Become an Expert https://www.physiciansplasma.com/leukapheresis-guide-ebook/leukapheresis-machine/