Mechanism of action, potency and efficacy: considerations for cell therapies.

One of the most challenging aspects of developing advanced cell therapy products (CTPs) is defining the mechanism of action (MOA), potency and efficacy of the product. This perspective examines these concepts and presents helpful ways to think about them through the lens of metrology. A logical framework for thinking about MOA, potency and efficacy is presented that is consistent with the existing regulatory guidelines, but also accommodates what has been learned from the 27 US FDA-approved CTPs. Available information regarding MOA, potency and efficacy for the 27 FDA-approved CTPs is reviewed to provide background and perspective. Potency process and efficacy process charts are introduced to clarify and illustrate the relationships between six key concepts: MOA, potency, potency test, efficacy, efficacy endpoint and efficacy endpoint test. Careful consideration of the meaning of these terms makes it easier to discuss the challenges of correlating potency test results with clinical outcomes and to understand how the relationships between the concepts can be misunderstood during development and clinical trials. Examples of how a product can be "potent but not efficacious" or "not potent but efficacious" are presented. Two example applications of the framework compare how MOA is assessed in cell cultures, animal models and human clinical trials and reveals the challenge of establishing MOA in humans. Lastly, important considerations for the development of potency tests for a CTP are discussed. These perspectives can help product developers set appropriate expectations for understanding a product's MOA and potency, avoid unrealistic assumptions and improve communication among team members during the development of CTPs.

Recommendations on fit-for-purpose criteria to establish quality management for microphysiological systems and for monitoring their reproducibility.

Cell culture technology has evolved, moving from single-cell and monolayer methods to 3D models like reaggregates, spheroids, and organoids, improved with bioengineering like microfabrication and bioprinting. These advancements, termed microphysiological systems (MPSs), closely replicate tissue environments and human physiology, enhancing research and biomedical uses. However, MPS complexity introduces standardization challenges, impacting reproducibility and trust. We offer guidelines for quality management and control criteria specific to MPSs, facilitating reliable outcomes without stifling innovation. Our fit-for-purpose recommendations provide actionable advice for achieving consistent MPS performance.

Acceptance criteria for new approach methods in toxicology and human health-relevant life science research - part I.

Every test procedure, scientific and non-scientific, has inherent uncertainties, even when performed according to a standard operating procedure (SOP). In addition, it is prone to errors, defects, and mistakes introduced by operators, laboratory equipment, or materials used. Adherence to an SOP and comprehensive validation of the test method cannot guarantee that each test run produces data within the acceptable range of variability and with the precision and accuracy determined during the method validation. We illustrate here (part I) why controlling the validity of each test run is an important element of experimental design. The definition and application of acceptance criteria (AC) for the validity of test runs is important for the setup and use of test methods, particularly for the use of new approach methods (NAM) in toxicity testing. AC can be used for decision rules on how to handle data, e.g., to accept the data for further use (AC fulfilled) or to reject the data (AC not fulfilled). The adherence to AC has important requirements and consequences that may seem surprising at first sight: (i) AC depend on a test method's objectives, e.g., on the types/concentrations of chemicals tested, the regulatory context, the desired throughput; (ii) AC are applied and documented at each test run, while validation of a method (including the definition of AC) is only performed once; (iii) if AC are altered, then the set of data produced by a method can change. AC, if missing, are the blind spot of quality assurance: Test results may not be reliable and comparable. The establishment and uses of AC will be further detailed in part II of this series.

ISSCR standards for the use of human stem cells in basic research.

The laboratory culture of human stem cells seeks to capture a cellular state as an in vitro surrogate of a biological system. For the results and outputs from this research to be accurate, meaningful, and durable, standards that ensure reproducibility and reliability of the data should be applied. Although such standards have been previously proposed for repositories and distribution centers, no widely accepted best practices exist for laboratory research with human pluripotent and tissue stem cells. To fill that void, the International Society for Stem Cell Research has developed a set of recommendations, including reporting criteria, for scientists in basic research laboratories. These criteria are designed to be technically and financially feasible and, when implemented, enhance the reproducibility and rigor of stem cell research.

History and current status of clinical studies using human pluripotent stem cells.

The Human Pluripotent Stem Cell Registry established a database of clinical studies using human pluripotent stem cells (PSCs) as starting material for cell therapies. Since 2018, we have observed a switch toward human induced pluripotent stem cells (iPSCs) from human embryonic stem cells. However, rather than using iPSCs for personalized medicines, allogeneic approaches dominate. Most treatments target ophthalmopathies, and genetically modified iPSCs are used to generate tailored cells. We observe a lack of standardization and transparency about the PSCs lines used, characterization of the PSC-derived cells, and the preclinical models and assays applied to show efficacy and safety.

An HLA-homozygous haplobank resource to promote safer cell therapies.

The generation of donor-derived induced pluripotent stem cells (iPSCs) for allogeneic transplantation is a major challenge in regenerative medicine. Yoshida et al. now report on the establishment of an HLA-homozygous haplobank of iPSCs that covers approximately 40% of the Japanese population and describe quality and safety considerations for manufacturing.

The consequences of recurrent genetic and epigenetic variants in human pluripotent stem cells.

It is well established that human pluripotent stem cells (hPSCs) can acquire genetic and epigenetic changes during culture in vitro. Given the increasing use of hPSCs in research and therapy and the vast expansion in the number of hPSC lines available for researchers, the International Society for Stem Cell Research has recognized the need to reassess quality control standards for ensuring the genetic integrity of hPSCs. Here, we summarize current knowledge of the nature of recurrent genetic and epigenetic variants in hPSC culture, the methods for their detection, and what is known concerning their effects on cell behavior in vitro or in vivo. We argue that the potential consequences of low-level contamination of cell therapy products with cells bearing oncogenic variants are essentially unknown at present. We highlight the key challenges facing the field with particular reference to safety assessment of hPSC-derived cellular therapeutics.

Implications of a Catastrophic Refrigeration Failure on the Viability of Cryogenically Stored Samples.

Cryopreservation, the use of very low temperatures to preserve structurally intact living cells and tissues, is a key underpinning technology for life science research and medicine. It is employed to ensure the stability of critical biological resources including viruses, bacteria, protists, animal cell cultures, plants, reproductive materials and embryos. Fundamental to ensuring this stability is assuring stability of cryogenic storage temperatures. Here we report the occurrence of a failure in refrigeration in a cryostat holding > 600 strains of cyanobacteria and eukaryotic microalgae. A strategic approach was adopted to assess viability across a cross-section of the biodiversity held, both immediately after the potentially damaging temperature shift and 10 years later, on subsequent cryostorage in liquid-phase nitrogen (∼-196 °C). Furthermore, the event was replicated experimentally and the effects on the viability of cryo-tolerant and cryo-sensitive strains monitored. Our results have significant implications to all users of this storage method and parallels have been drawn with the ongoing development in other fields and in particular, human cell therapy. Based on our practical experience we have made a series of generic recommendations for emergency, remedial and ongoing preventative actions.

Manufacturing with pluripotent stem cells (PSConf 2021): Key issues for future research and development.

Human pluripotent stem cells (hPSC) have the capability to deliver novel cell-based medicines that could transform medical treatments for a wide range of diseases including age-related degenerative disorders and traumatic injury. In spite of significant investment in this area, due to the novel nature of these hPSC-based medicines, there are challenges in almost all aspects of their manufacturing including bioprocessing, characterization and delivery. The Chinese Academy of Sciences and the Chinese Society for Stem Cell Research have collaborated to create a new discussion forum called PSConf 2021 (Pluripotent Stem Cell Conference 2021), intended to promote exchanges in communication on cutting-edge developments and international coordination in hPSC manufacturing. The PSConf 2021 addressed crucial topics in stem cell-based manufacturing, including stem cell differentiation, culture scale-up, product formulation and release. This report summarizes the proceedings and conclusions from the discussion sessions, and it is accompanied by publication of individual papers from the speakers at the PSConf 2021. SIGNIFICANCE STATEMENT: The PSConf 2021 meeting has brought together speakers and delegates from more than 20 countries in an informal discussion forum focusing on the manufacture of cell-based medicines using hPSCs. The conference discussion sessions enabled an open exchange of information on the latest developments, ideas on key challenges and their potential solutions. It also captured the experiences and lessons learnt by professionals who had been in the field from the earliest applications of human embryonic stem cells, and presented a diverse range of new potential pluripotent stem cell-based medicines that are now under development, with some already in clinical trials.

Single-cell transcriptomics reveals the cell fate transitions of human dopaminergic progenitors derived from hESCs.

BACKGROUND: Midbrain dopaminergic (DA) progenitors derived from human pluripotent stem cells are considered to be a promising treatment for Parkinson's disease (PD). However, the differentiation process produces undesired cell types, which influence the in vivo evaluation of DA cells. In this paper, we analyze the cell fate choice during differentiation and provide valuable information on cell preparation. METHODS: Human embryonic stem cells were differentiated into DA progenitors. We applied single-cell RNA sequencing (scRNA-seq) of the differentiation cells at different time points and investigated the gene expression profiles. Based on the differentially expressed genes between DA and non-DA cells, we investigated the impact of LGI1 (DA enriched) overexpression on DA differentiation and the enrichment effect of CD99 (non-DA enriched) sorting. RESULTS: Transcriptome analyses revealed the DA differentiation trajectory as well as non-DA populations and three key lineage branch points. Using genetic gain- and loss-of-function approaches, we found that overexpression of LGI1, which is specific to EN1+ early DA progenitors, can promote the generation of TH+ neurons. We also found that choroid plexus epithelial cells and DA progenitors are major components of the final product (day 25), and CD99 was a specific surface marker of choroid plexus epithelial cells. Sorting of CD99- cells eliminated major contaminant cells and improved the purity of DA progenitors. CONCLUSIONS: Our study provides the single-cell transcriptional landscape of in vitro DA differentiation, which can guide future improvements in DA preparation and quality control for PD cell therapy.

Quality criteria for in vitro human pluripotent stem cell-derived models of tissue-based cells.

The advent of the technology to isolate or generate human pluripotent stem cells provided the potential to develop a wide range of human models that could enhance understanding of mechanisms underlying human development and disease. These systems are now beginning to mature and provide the basis for the development of in vitro assays suitable to understand the biological processes involved in the multi-organ systems of the human body, and will improve strategies for diagnosis, prevention, therapies and precision medicine. Induced pluripotent stem cell lines are prone to phenotypic and genotypic changes and donor/clone dependent variability, which means that it is important to identify the most appropriate characterization markers and quality control measures when sourcing new cell lines and assessing differentiated cell and tissue culture preparations for experimental work. This paper considers those core quality control measures for human pluripotent stem cell lines and evaluates the state of play in the development of key functional markers for their differentiated cell derivatives to promote assurance of reproducibility of scientific data derived from pluripotent stem cell-based systems.

Biobanking of human pluripotent stem cells in China.

In recent years, significant progress has been made internationally in the development of human pluripotent stem cell (hPSC)-derived products for serious and widespread disorders. Biobanking of the cellular starting materials is a crucial component in the delivery of safe and regulatory compliant cell therapies. In China, key players in these developments have been the recently launched National Stem Cell Resource Center (NSCRC) and its partner organizations in Guangzhou and Shanghai who together, have more than 600 hPSC lines formally recorded in the Chinese Ministry of Science and Technology's stem cell registry. In addition, 47 of these hPSCs have also been registered with the hPSCreg project which means they are independently certified for use in European Commission funded research projects. The NSCRC are currently using their own cell lines to manufacture eight different cell types qualified for clinical use, that are being used in nine clinical studies for different indications. The Institute of Zoology at the Chinese Academy of Sciences (IOZ-CAS) has worked with NSCRC to establish Chinese and international standards in stem cell research. IOZ-CAS was also a founding partner in the International Stem Cell Banking Initiative which brings together key stem cell banks to agree minimum standards for the provision of pluripotent stem cells for research and clinical use. Here, we describe recent developments in China in the establishment of hPSCs for use in the manufacture of cell therapies and the significant national and international coordination which has now been established to promote the translation of Chinese hPSC-based products into clinical use according to national and international standards.

Translating stem cell research into development of cellular drugs-a perspective from manufacture of stem cell products and CMC considerations.

The development of human pluripotent stem cell (PSC)-derived medicinal products has been gathering steam in recent years, but the translation of research protocols into GMP production remains a daunting task. The challenges not only reside with the nature of cellular therapeutics but are also rooted in the general inexperience in industry-scale production of stem cell products. Manufacturers of PSC-derived products should be aware of the technical nuances and take a holistic approach toward early planning and engagement with their academic partners. While not all issues will be readily resolved soon, the collective knowledge and consensus by the manufacturers and key stakeholders will help to guide rapid progression of the field.

Human retinal pigment epithelial cells.

'Human retinal pigment epithelial cells' is the first set of guidelines on human retinal pigment epithelial cells in China, jointly drafted and agreed upon by experts from the Chinese Society for Stem Cell Research. This standard specifies technical requirements, test methods, inspection rules, instructions for usage, labelling requirements, packaging requirements, storage requirements and transportation requirements and waste disposal requirements for human retinal pigment epithelial cells, which is applicable to quality control during the process of manufacturing and testing of human retinal pigment epithelial cells. It was originally released by the Chinese Society for Cell Biology on 9 January 2021. We hope that publication of these guidelines will promote institutional establishment, acceptance and execution of proper protocols and accelerate the international standardization of human retinal pigment epithelial cells for applications.

Guidance document on Good Cell and Tissue Culture Practice 2.0 (GCCP 2.0).

Good Cell and Tissue Culture Practice (GCCP) 2.0 is an updated guidance document from GCCP 1.0 (published by ECVAM in 2005), which was developed for practical use in the laboratory to assure the reproducibility of in vitro (cell-based) work. The update in the guidance was essential as cell models have advanced dramatically to more complex culture systems and need more comprehensive quality management to ensure reproducibility and high-quality scientific data. This document describes six main principles to consider when performing cell culture including characterization and maintenance of essential characteristics, quality management, documentation and reporting, safety, education and training, and ethics. The document does not intend to impose detailed procedures but to describe potential quality issues. It is foreseen that the document will require further updates as the science and technologies evolve over time.

Neuronal cell-based medicines from pluripotent stem cells: Development, production, and preclinical assessment.

Brain degeneration and damage is difficult to cure due to the limited endogenous repair capability of the central nervous system. Furthermore, drug development for treatment of diseases of the central nervous system remains a major challenge. However, it now appears that using human pluripotent stem cell-derived neural cells to replace degenerating cells provides a promising cell-based medicine for rejuvenation of brain function. Accordingly, a large number of studies have carried out preclinical assessments, which have involved different neural cell types in several neurological diseases. Recent advances in animal models identify the transplantation of neural derivatives from pluripotent stem cells as a promising path toward the clinical application of cell therapies [Stem Cells Transl Med 2019;8:681-693; Drug Discov Today 2019;24:992-999; Nat Med 2019;25:1045-1053]. Some groups are moving toward clinical testing in humans. However, the difficulty in selection of valuable critical quality criteria for cell products and the lack of functional assays that could indicate suitability for clinical effect continue to hinder neural cell-based medicine development [Biologicals 2019;59:68-71]. In this review, we summarize the current status of preclinical studies progress in this area and outline the biological characteristics of neural cells that have been used in new developing clinical studies. We also discuss the requirements for translation of stem cell-derived neural cells in examples of stem cell-based clinical therapy.