Main Text
Cell therapies are taking center stage in medicine spanning cancer immunotherapy, stem cell engineering, and regenerative medicine. Recently, the first ex vivo hematopoietic stem cell (HSC) gene therapy for the treatment of adenosine deaminase deficiency-severe combined immunodeficiency (ADA-SCID) received marketing approval.1 By now, the majority of the 150 plus patients who have received HSC gene therapy to treat monogenic diseases have demonstrated clinical benefits.2 Promising clinical outcomes in phase I/II trials based on T cells engineered to express T cell chimeric antigen receptors (CARs)3 against hematological malignancies have also spurred unprecedented interest from pharmaceutical and biotechnology companies. As a result, CD19-targeted CAR T cells may soon receive marketing approval.4
As living drugs, cell therapies pose unique commercialization challenges in terms of manufacturing, standardization, and distribution.4, 5, 6 Automated, robust, and cost-effective production platforms compliant with current good manufacturing practices (cGMP) coupled with robust analytics, which ensure reproducible cell quality, are needed to broaden the availability and realize the commercialization potential of these complex, predominantly personalized, therapeutic modalities.
HSC and CAR-T cell engineering processes commonly start from an autologous or donor apheresis. The inter-institution and inter-patient variability that are inherent to apheresis collection and composition, the paucity of well-defined and quantifiable critical quality attributes (CQAs), and the requirement for cGMP-grade culture media components and ancillary genetic modifiers, such as viral vectors and CRISPR/Cas9 components, add to the complexity of these therapeutic modalities.5, 6, 7
To decrease the production scale and shorten the time in culture, cell subsets known to provide optimal therapeutic effects and limited toxicities may be selected to initiate manufacturing8, 9 or may be selectively expanded/differentiated during manufacturing. Unfortunately, for most cell therapies, these biological attributes are not yet well characterized and are likely to depend upon not only the cell type and source, but also the specific disease condition and patient profile.
Biological Barriers
To establish robust and reproducible manufacturing processes, it is advisable to follow quality-by-design (QbD) principles.10 Quantifiable molecular and cellular characteristics that ensure product safety, efficacy, and potency should enable and drive the manufacturing processes from starting material to final product. This approach is contingent first upon understanding how the specific cells function in vivo in the context of a particular disease and second upon inclusion of CQAs that underlie the therapeutic benefits independently of patient variables. The scarcity of functional CQAs and consequently of early indicators of quality or batch failures poses a high risk for industry. For example, there is a need for better understanding of cell biophysics and how the microenvironment affects cell function.
Technological Barriers
Besides a few metabolites and culture conditions, such as pH or oxygen content, most manufacturing platforms do not support integrated analytical tools to measure cell properties related to potency, safety, and contamination. Process analytical technologies (PATs), including non-destructive, integrated, and image-based sensors, that can provide feedback on cell quality in real time need to be developed.11 Human-like safety and potency assays (e.g., tissue-on-chip or related organoid models) as well as induced pluripotent stem cell (iPSC)-derived disease models may help broaden the spectrum of available biological assays. The concept of critical process parameters (CPPs) to control cell quality, how they affect cell quality, and how to control them is important in order to achieve robust manufacturing processes. These are dependent upon identification of the CQAs through deep characterization and biological studies enabled by informatics, machine learning, and big data analytics.
Automation
To mitigate costly cGMP operations, laborious manual procedures, and their inherent reproducibility issues, as well as to reduce risk of contamination, closed automated systems that integrate bioreactors and robotics are required. Beyond automation, the inherent variability of source cells, especially autologous cells, necessitates the inclusion of flexible built-in process automation that can be adjusted based on CQA measurements and on feedback from real-time analytics.5, 6, 12 Novel cell separation technologies, such as acoustic waves, microfluidic separation platforms,13 and phase-change hydrogel substrates,14 may be integrated into these systems. Further enrichment of specific cell subsets may be promoted by cytokines or small molecules whose biological activities need to be defined against established standards.6
Standards
The biological activities of raw materials (e.g., cytokines and small molecules) can significantly alter the potency and safety profile of cell products. Very few reference and measurement standards are yet available across the field. Various groups are using different material sources, assays, equipment, and techniques of data analysis. In the absence of standards, this multiplicity of approaches confounds comparability and cross validation of data. Consensus best practices and measurement assurance guidelines must be developed along with eventual standards. Standardized analytical tools to assess relevant CQAs are direly needed.
Formulation and Distribution
Reliance on cryopreservation requires that we better understand how freezing and thawing affect cell function and safety. It also limits wide distribution owing to constraints in storage and transportation.6 Future research should explore improved and alternative methods for live cell transportation that integrate measurements of product quality.
Workforce
The lack of a biomanufacturing workforce that is well trained in cGMP procedures and analytics and that could populate clinical and industrial manufacturing settings is seriously hampering the progress and translation of cell therapies. Significant investment in developing such a workforce—both at the level of 2-year community or technical colleges or standard 4-year universities—is critically needed.
Prospective Solutions
Robust investment in basic science and human-like disease models are crucial to elucidate how complex cell-based products function. Understanding how donor/patient variability effects source cell properties and consequently manufacturing and how recipient pathophysiology affects treatment outcome is also critical. Ensuing CQAs derived from such analyses will guide the design of combined manufacturing and analytic platforms.
National Institute of Standards and Technology (NIST), the Food and Drug Administration (FDA), the Alliance for Regenerative Medicine (https://alliancerm.org/press/alliance-regenerative-medicine-launches-standards-coordinating-body-advance-development-and) and other stakeholders are coordinating task forces to develop standards and plan on publishing white papers that will help develop guidelines (https://www.nist.gov/news-events/events/2017/04/nist-fda-cell-counting-workshop-sharing-practices-cell-counting). Recently, a Standards Coordinating Body was established with public-private partnerships to facilitate standards development in this space (http://www.regenmedscb.org/). In 2016, a US national roadmap on cell therapy manufacturing was established upon a unique collaboration between companies, academic institutions, and government agencies to accelerate the path to commercialization (http://cellmanufacturingusa.org/road-map). The rise of cell therapies has spurred the development of consortia, such as CCRM (http://ccrm.ca), NIIMBL (http://www.niimbl.us), MC3M (http://www.cellmanufacturing.gatech.edu), Catapult (https://ct.catapult.org.uk), and ARMI (https://www.defense.gov/News/News-Releases/News-Release-View/Article/1035759/dod-announces-award-of-new-advanced-tissue-biofabrication-manufacturing-innovat), and the recent involvement of biotech and pharmaceutical companies. In addition, the US National Academies have established a forum on Regenerative Medicine (http://nationalacademies.org/hmd/Activities/Research/RegenerativeMedicine.aspx) in which manufacturing is a major focus. These major efforts will not only enable the production of optimal cellular components with increased safety, efficacy, robustness, and reproducibility profiles, but will also decrease cost and increase access to these potent cell therapies.
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