The specifications, QC and release testing of cell therapy products can make the difference between success and failure

Stefanos Theoharis, Suncana Kern and Christine Guenther, apceth GmbH & Co. KG. All manufactured products require measurable parameters, called specifications, which confirm each manufacturing run has met the specifications. Quality Control (QC) is the process of establishing and testing them. The more complex and sophisticated the product, the more parameters must be tested and cell therapy products are among the most complex. Cells are living organisms with multiple features determining their therapeutic function. Product specifications must reflect those critical features, and QC tests must be developed for the starting material, the process-related parameters and the end product, characterized by these mandatory criteria:

Identity: The identity of product is established using unique distinguishing characteristics, usually cell-surface proteins. For example, all haematopoietic stem cells express CD34 and all T-cells CD3. Mesenchymal stem cells (MSCs), a very common cell type in clinical trials, must be positive for CD73, CD105, CD90 and negative for CD45 and CD34. Other markers may also be tested for absence (e.g. CD14/CD11b, CD79alpha/CD19 and HLA-DR). They are also able to differentiate to osteoblasts, adipocytes and chondrocytes. So, for MSC products a panel of at least 5 surface molecules and 3 differentiation tests are common practice. Engineered cells, like the genetically modified MSCs developed by apceth (e.g. Agenmestencel-T currently in Phase II clinical trial), also feature a new gene and its gene product. It’s therefore necessary to test for this with appropriate thresholds to ensure therapeutic efficacy and safety.

Purity: It’s impossible to ensure that the final cell population will be 100% homogenous, since the starting material is human material and the manufacturing process involves multiple steps which affect cells differently. A cut-off for minimum purity must be decided based on the mode of action of the cell product. Likewise, there should be a cut-off for cell viability, post-production or post-thawing, and for all other cellular components.

Sterility/mycoplasma/endotoxin: All pharmaceutical products are manufactured under aseptic conditions to ensure sterility and are tested for bacterial, fungal, mycoplasma and endotoxin contamination. These tests are standardized and straightforward, but must be validated for each product. Allogeneic cell products are based on donor-derived cells, expanded to yield multiple doses (off-the-shelf product). This is possible without any modifications for MSCs and has multiple advantages concerning the quality and reproducibility, cost, logistics and product availability. Allogeneic products additionally involve donor testing for transmissible diseases (similar to cord blood donations).

Potency: This category refers to tests that predict the product will exhibit the necessary functionality for therapeutic efficacy, every time. They may include expression of relevant proteins, the genomic signature of cells or an in vitro functional assay. It’s best to keep these very simple, with clear readouts. A reference standard may be useful.

Stability/ genetic stability: The in-use stability is critical for delivering reproducible results of cell products (freshly applied or frozen) influencing significantly the product quality. Genetic stability refers to the expanded cultivation process of some cell types which might influence the product quality and safety. In conclusion, the specifications of cell therapy products are complex and QC is cumbersome. Automation is likely to reduce the workload and cost of QC and manufacturing, but the prime consideration must always be to ensure high standards that translate to therapeutic benefit for patients in need.