Do we Still Need Human Embryonic Stem Cells for Stem Cell-Based Therapies? Epistemic and Ethical Aspects

Ethical Aspects of Human Induced Pluripotent Stem Cells and Alzheimer's Disease: Potentials and Challenges of a Seemingly Harmless Method

Dementia currently affects more than 55 million people worldwide, and scientists predict that this number will continue to rise. The most common form is Alzheimer's disease (AD), which is triggered, among other things, by dysfunctional cells in the human brain. Stem cell research attempts to counteract neurodegenerative processes, for example by replacing or treating diseased cells. In addition to human embryonic stem cells, since the successes of Takahashi and Yamanaka in 2006, there has been an increased focus on human induced pluripotent stem cells (hiPS cells). These cells avoid ethically challenging questions about the moral status of human embryos, but there are numerous problems, such as high production costs, side effects from the reprogramming process, or a potentially new moral status. These ethical issues will be examined primarily in relation to AD. The first part will be a discussion of hiPS cells and their importance for stem cell research, after which the focus turns to AD. Based on scientific studies, the relationship between hiPS cells and AD will be outlined as well as ethical implications presented. While potential limitations of hiPS cells have been discussed by numerous authors, an ethical perspective on the link between hiPS cells and AD seems to be neglected in the scientific community. The following risk analysis aims to identify a possible research agenda. In conclusion, the focus on individuals with AD may help to adopt an ethical stance that recognizes existing limitations and constructively engages with the possibilities of research.

The Ethical Implications of Tissue Engineering for Regenerative Purposes: A Systematic Review

Tissue Engineering (TE) is a branch of Regenerative Medicine (RM) that combines stem cells and biomaterial scaffolds to create living tissue constructs to restore patients' organs after injury or disease. Over the last decade, emerging technologies such as 3D bioprinting, biofabrication, supramolecular materials, induced pluripotent stem cells, and organoids have entered the field. While this rapidly evolving field is expected to have great therapeutic potential, its development from bench to bedside presents several ethical and societal challenges. To make sure TE will reach its ultimate goal of improving patient welfare, these challenges should be mapped out and evaluated. Therefore, we performed a systematic review of the ethical implications of the development and application of TE for regenerative purposes, as mentioned in the academic literature. A search query in PubMed, Embase, Scopus, and PhilPapers yielded 2451 unique articles. After systematic screening, 237 relevant ethical and biomedical articles published between 2008 and 2021 were included in our review. We identified a broad range of ethical implications that could be categorized under 10 themes. Seven themes trace the development from bench to bedside: (1) animal experimentation, (2) handling human tissue, (3) informed consent, (4) therapeutic potential, (5) risk and safety, (6) clinical translation, and (7) societal impact. Three themes represent ethical safeguards relevant to all developmental phases: (8) scientific integrity, (9) regulation, and (10) patient and public involvement. This review reveals that since 2008 a significant body of literature has emerged on how to design clinical trials for TE in a responsible manner. However, several topics remain in need of more attention. These include the acceptability of alternative translational pathways outside clinical trials, soft impacts on society and questions of ownership over engineered tissues. Overall, this overview of the ethical and societal implications of the field will help promote responsible development of new interventions in TE and RM. It can also serve as a valuable resource and educational tool for scientists, engineers, and clinicians in the field by providing an overview of the ethical considerations relevant to their work. Impact statement To our knowledge, this is the first time that the ethical implications of Tissue Engineering (TE) have been reviewed systematically. By gathering existing scholarly work and identifying knowledge gaps, this review facilitates further research into the ethical and societal implications of TE and Regenerative Medicine (RM) and other emerging biomedical technologies. Moreover, it will serve as a valuable resource and educational tool for scientists, engineers, and clinicians in the field by providing an overview of the ethical considerations relevant to their work. As such, our review may promote successful and responsible development of new strategies in TE and RM.

Myt1l induced direct reprogramming of pericytes into cholinergic neurons

OBJECTIVE

The cholinergic deficit is thought to underlie progressed cognitive decline in Alzheimer Disease. The lineage reprogramming of somatic cells into cholinergic neurons may provide strategies toward cell-based therapy of neurodegenerative diseases.

METHODS AND RESULTS

Here, we found that a combination of neuronal transcription factors, including Ascl1, Myt1l, Brn2, Tlx3, and miR124 (5Fs) were capable of directly converting human brain vascular pericytes (HBVPs) into cholinergic neuronal cells. Intriguingly, the inducible effect screening of reprogramming factors showed that a single reprogramming factor, Myt1l, induced cells to exhibit similarly positive staining for Tuj1, MAP2, ChAT, and VAChT upon lentivirus infection with the 5Fs after 30 days. HBVP-converted neurons were rarely labeled even after long-term incubation with BrdU staining, suggesting that induced neurons were directly converted from HBVPs rather than passing through a proliferative state. In addition, the overexpression of Myt1l induced the elevation of Ascl1, Brn2, and Ngn2 levels that contributed to reprogramming.

CONCLUSIONS

Our findings provided proof of the principle that cholinergic neurons could be produced from HBVPs by reprogramming factor-mediated fate instruction. Myt1l was a critical mediator of induced neuron cell reprogramming. HBVPs represent another excellent alternative cell resource for cell-based therapy to treat neurodegenerative disease.

Neurotrophin Signaling and Stem Cells-Implications for Neurodegenerative Diseases and Stem Cell Therapy

Neurotrophins (NTs) are members of a neuronal growth factor protein family whose action is mediated by the tropomyosin receptor kinase (TRK) receptor family receptors and the p75 NT receptor (p75NTR), a member of the tumor necrosis factor (TNF) receptor family. Although NTs were first discovered in neurons, recent studies have suggested that NTs and their receptors are expressed in various types of stem cells mediating pivotal signaling events in stem cell biology. The concept of stem cell therapy has already attracted much attention as a potential strategy for the treatment of neurodegenerative diseases (NDs). Strikingly, NTs, proNTs, and their receptors are gaining interest as key regulators of stem cells differentiation, survival, self-renewal, plasticity, and migration. In this review, we elaborate the recent progress in understanding of NTs and their action on various stem cells. First, we provide current knowledge of NTs, proNTs, and their receptor isoforms and signaling pathways. Subsequently, we describe recent advances in the understanding of NT activities in various stem cells and their role in NDs, particularly Alzheimer's disease (AD) and Parkinson's disease (PD). Finally, we compile the implications of NTs and stem cells from a clinical perspective and discuss the challenges with regard to transplantation therapy for treatment of AD and PD.

Accelerating stem cell trials for Alzheimer's disease

At present, no effective cure or prophylaxis exists for Alzheimer's disease. Symptomatic treatments are modestly effective and offer only temporary benefit. Advances in induced pluripotent stem cell (iPSC) technology have the potential to enable development of so-called disease-in-a-dish personalised models to study disease mechanisms and reveal new therapeutic approaches, and large panels of iPSCs enable rapid screening of potential drug candidates. Different cell types can also be produced for therapeutic use. In 2015, the US Food and Drug Administration granted investigational new drug approval for the first phase 2A clinical trial of ischaemia-tolerant mesenchymal stem cells to treat Alzheimer's disease in the USA. Similar trials are either underway or being planned in Europe and Asia. Although safety and ethical concerns remain, we call for the acceleration of human stem cell-based translational research into the causes and potential treatments of Alzheimer's disease.

Ethical Issues for Clinical Studies That use Human Embryonic Stem Cells: The 2014 Revisions to the Japanese Guidelines

The use of human embryonic stem cells (hESCs) in clinical studies has been expanding in recent years. The application of hESCs in clinical studies raises ethical issues from a different standpoint compared with the use of other types of stem cells. In Japan, the Guidelines on the Derivation of Human Embryonic Stem Cells, and Guidelines on the Distribution and Utilization of Human Embryonic Stem Cells had been revised for clinical studies in 2014. In the revised guidelines, the method for protection of personal information was changed to offer the choice between unlinkable anonymization and linkable anonymization, to enable the use of information on diseases suffered by donors and the assurance of traceability for safety. Procedures for re-consent are generally prohibited out of consideration for donors' feelings. However, obtaining re-consent is permitted when consent for re-consent has been received in advance and approval has been given by an ethical review board, in which case the donors may be contacted. Incidental findings obtained from hESCs are not disclosed individually to donors, while the research results should be actively published for the common good. These guidelines have enabled the derivation, distribution, and use of hESCs for clinical studies.

The safety of human pluripotent stem cells in clinical treatment

Human pluripotent stem cells (hPSCs) have practically unlimited proliferation potential and a capability to differentiate into any cell type in the human body. Since the first derivation in 1998, they have been an attractive source of cells for regenerative medicine. Numerous ethical, technological, and regulatory complications have been hampering hPSC use in clinical applications. Human embryonic stem cells (ESCs), parthenogenetic human ESCs, human nuclear transfer ESCs, and induced pluripotent stem cells are four types of hPSCs that are different in many clinically relevant features such as propensity to epigenetic abnormalities, generation methods, and ability for development of autologous cell lines. Propensity to genetic mutations and tumorigenicity are common features of all pluripotent cells that complicate hPSC-based therapies. Several recent advances in methods of derivation, culturing, and monitoring of hPSCs have addressed many ethical concerns and technological challenges in development of clinical-grade hPSC lines. Generation of banks of such lines may be useful to minimize immune rejection of hPSC-derived allografts. In this review, we discuss different sources of hPSCs available at the moment, various safety risks associated with them, and possible solutions for successful use of hPSCs in the clinic. We also discuss ongoing clinical trials of hPSC-based treatments.

Reawakening atlas: chemical approaches to repair or replace dysfunctional musculature

Muscle diseases are major health concerns. For example, ischemic heart disease is the third most common cause of death. Cell therapy is an attractive approach for treating muscle diseases, although this is hampered by the need to generate large numbers of functional muscle cells. Small molecules have become established as attractive tools for modulating cell behavior and, in this review, we discuss the recent, rapid research advances made in the development of small molecule methods to facilitate the production of functional cardiac, skeletal, and smooth muscle cells. We also describe how new developments in small molecule strategies for muscle disease aim to induce repair and remodelling of the damaged tissues in situ. Recent progress has been made in developing small molecule cocktails that induce skeletal muscle regeneration, and these are discussed in a broader context, because a similar phenomenon occurs in the early stages of salamander appendage regeneration. Although formidable technical hurdles still remain, these new advances in small molecule-based methodologies should provide hope that cell therapies for patients suffering from muscle disease can be developed in the near future.

Autologous stem cells for personalised medicine

Increasing understanding of stem cell biology, the ability to reprogramme differentiated cells to a pluripotent state and evidence of multipotency in certain adult somatic stem cells has opened the door to exciting therapeutic advances as well as a great deal of regulatory and ethical issues. Benefits will come from the possibility of modelling human diseases and develop individualised therapies, and from their use in transplantation and bioengineering. The use of autologous stem cells is highly desirable, as it avoids the problem of tissue rejection, and also reduces ethical and regulatory issues. Identification of the most appropriate cell sources for different potential applications, development of appropriate clinical grade methodologies and large scale well controlled clinical trials will be essential to assess safety and value of cell based therapies, which have been generating much hope, but are by and large not yet close to becoming standard clinical practice. We briefly discuss stem cells in the context of tissue repair and regenerative medicine, with a focus on individualised clinical approaches, and give examples of sources of autologous cells with potential for clinical intervention.

Cardiac cell therapy: pre-conditioning effects in cell-delivery strategies

Stem-cell therapy holds great promise for the treatment of ischemic heart disease. However, the benefit of cardiac cell therapy has not yet been proven in long-term clinical trials. Poor engraftment and survival of transplanted cells is one of the major concerns for the successful application of stem cells in cardiac cell therapy. Cell and cardiac pre-conditioning are now being explored as new approaches to support cell survival and enhance the therapeutic efficacy. In this paper, we summarize the state-of-the-art methods of cell delivery and cell survival post-delivery, with a focus on the pre-conditioning approaches that have been attempted to support the survival of transplanted cells.