Loss of tumorigenic potential upon transdifferentiation from keratinocytic into melanocytic lineage

Bioengineering strategies for regeneration of skin integrity: A literature review

Objective

The skin is a complex organ that includes various stem cell populations. Current approaches for non-healing skin defects are sometimes inadequate and many attempts have been made to regenerate skin integrity. The aim of this review is to bridge the gap between basic research and clinical application of skin integrity regeneration.

Methods

A literature search was carried out in PubMed using combinations of the keywords "skin integrity", "tissue-engineered skin", "bioengineered skin", and "skin regeneration". Articles published from 1968 to 2023 reporting evidence from in vivo and in vitro skin regeneration experiments were included.

Results

These articles showed that stem cells can be differentiated into normal skin cells, including keratinocytes, and are a significant source of skin organoids, which are useful for investigating skin biology; and that emerging direct reprogramming methods have great potential to regenerate skin from the wounded skin surface.

Conclusion

Recent advances in skin regeneration will facilitate further advancement of both basic and clinical research in skin biology.

Therapeutic approaches of cell therapy based on stem cells and terminally differentiated cells: Potential and effectiveness

Cell-based therapy, as a promising regenerative medicine approach, has been a promising and effective strategy to treat or even cure various kinds of diseases and conditions. Generally, two types of cells are used in cell therapy, the first is the stem cell, and the other is a fully differentiated cell. Initially, all cells in the body are derived from stem cells. Based on the capacity, potency and differentiation potential of stem cells, there are four types: totipotent (produces all somatic cells plus perinatal tissues), pluripotent (produces all somatic cells), multipotent (produces many types of cells), and unipotent (produces a particular type of cells). All non-totipotent stem cells can be used for cell therapy, depending on their potency and/or disease state/conditions. Adult fully differentiated cell is another cell type for cell therapy that is isolated from adult tissues or obtained following the differentiation of stem cells. The cells can then be transplanted back into the patient to replace damaged or malfunctioning cells, promote tissue repair, or enhance the targeted organ's overall function. With increasing science and knowledge in biology and medicine, different types of techniques have been developed to obtain efficient cells to use for therapeutic approaches. In this study, the potential and opportunity of use of all cell types, both stem cells and fully differentiated cells, are reviewed.

Limitations and challenges of direct cell reprogramming in vitro and in vivo

Direct reprogramming, whether in vitro or in vivo, has attracted great attention because of its advantages of convenience, short-term conversion, direct targets, no immune rejection, and potential clinical applications. In addition, due to its independence from the pluripotent state, direct programming minimizes some safety concerns associated with the use of human pluripotent stem cells. However, the significant limitations of reprogrammed cells, such as poor proliferative ability, low efficiency, and immature function, need to be addressed before the clinical application potential can be expanded. Here, we review the recent achievements of direct reprogramming in 2D and 3D systems in vitro and in vivo, covering cells derived from the three germ layers from stem/progenitor cells to terminal cells, such as hepatocytes, pancreatic β cells, cardiomyocytes, endothelial cells, osteoblasts, chondrocytes, neurons, and melanocytes. Combining our lab experiences with current work, we summarize the practical and potential issues that need to be solved and the prospects of strategies for addressing the current dilemmas. Through comprehensive analyses, it is concluded that the directions for dealing with efficiency and functionality issues could be the optimization of transcription factors, the upgradation for delivery systems, the regulation of epigenetic factors and pathways, and the improvement of cellular maintenance conditions. Besides, converting cells into the progenitor state firstly and then differentiating them into the desired cell types with chemical compounds may provide an approach to obtaining functional and safe converted cells in batches with a better proliferative ability. With the emergence of more and more direct reprogramming techniques and approaches with both safety and effectiveness, it is bound to bring a new dawn for mechanism research and therapeutic applications for relevant diseases in the future.

Cell Fate Reprogramming in the Era of Cancer Immunotherapy

Advances in understanding how cancer cells interact with the immune system allowed the development of immunotherapeutic strategies, harnessing patients' immune system to fight cancer. Dendritic cell-based vaccines are being explored to reactivate anti-tumor adaptive immunity. Immune checkpoint inhibitors and chimeric antigen receptor T-cells (CAR T) were however the main approaches that catapulted the therapeutic success of immunotherapy. Despite their success across a broad range of human cancers, many challenges remain for basic understanding and clinical progress as only a minority of patients benefit from immunotherapy. In addition, cellular immunotherapies face important limitations imposed by the availability and quality of immune cells isolated from donors. Cell fate reprogramming is offering interesting alternatives to meet these challenges. Induced pluripotent stem cell (iPSC) technology not only enables studying immune cell specification but also serves as a platform for the differentiation of a myriad of clinically useful immune cells including T-cells, NK cells, or monocytes at scale. Moreover, the utilization of iPSCs allows introduction of genetic modifications and generation of T/NK cells with enhanced anti-tumor properties. Immune cells, such as macrophages and dendritic cells, can also be generated by direct cellular reprogramming employing lineage-specific master regulators bypassing the pluripotent stage. Thus, the cellular reprogramming toolbox is now providing the means to address the potential of patient-tailored immune cell types for cancer immunotherapy. In parallel, development of viral vectors for gene delivery has opened the door for in vivo reprogramming in regenerative medicine, an elegant strategy circumventing the current limitations of in vitro cell manipulation. An analogous paradigm has been recently developed in cancer immunotherapy by the generation of CAR T-cells in vivo. These new ideas on endogenous reprogramming, cross-fertilized from the fields of regenerative medicine and gene therapy, are opening exciting avenues for direct modulation of immune or tumor cells in situ, widening our strategies to remove cancer immunotherapy roadblocks. Here, we review current strategies for cancer immunotherapy, summarize technologies for generation of immune cells by cell fate reprogramming as well as highlight the future potential of inducing these unique cell identities in vivo, providing new and exciting tools for the fast-paced field of cancer immunotherapy.

Therapeutic Potential of Patient iPSC-Derived iMelanocytes in Autologous Transplantation

Induced pluripotent stem cells (iPSCs) are a promising melanocyte source as they propagate indefinitely and can be established from patients. However, the in vivo functions of human iPSC-derived melanocytes (hiMels) remain unknown. Here, we generated hiMels from vitiligo patients using a three-dimensional system with enhanced differentiation efficiency, which showed characteristics of human epidermal melanocytes with high sequence similarity and involved in multiple vitiligo-associated signaling pathways. A modified hair follicle reconstitution assay in vivo showed that MITF+PAX3+TYRP1+ hiMels were localized in the mouse hair bulb and epidermis and produced melanin up to 7 weeks after transplantation, whereas MITF+PAX3+TYRP1- hiMelanocyte stem cells integrated into the bulge-subbulge regions. Overall, these data demonstrate the long-term functions of hiMels in vivo to reconstitute pigmented hair follicles and to integrate into normal regions for both mature melanocytes and melanocyte stem cells, providing an alternative source of personalized cellular therapy for depigmentation.

Melanoma-Derived iPCCs Show Differential Tumorigenicity and Therapy Response

A point mutation in the BRAF gene, leading to a constitutively active form of the protein, is present in 45%–60% of patients and acts as a key driver in melanoma. Shortly after therapy induction, resistance to MAPK pathway-specific inhibitors develops, indicating that pathway inhibition is circumvented by epigenetic mechanisms. Here, we mimicked epigenetic modifications in melanoma cells by reprogramming them into metastable induced pluripotent cancer cells (iPCCs) with the ability to terminally differentiate into non-tumorigenic lineages. iPCCs and their differentiated progeny were characterized by an increased resistance against targeted therapies, although the cells harbor the same oncogenic mutations and signaling activity as the parental melanoma cells. Furthermore, induction of a pluripotent state allowed the melanoma-derived cells to acquire a non-tumorigenic cell fate, further suggesting that tumorigenicity is influenced by the cell state.

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Human melanoma cells reprogrammed toward an iPSC-like state (iPCCs)

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iPCCs differentiated into neurons and fibroblasts

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iPCC-derived fibroblasts show no tumorigenic potential

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iPCCs and iPCC-derived fibroblasts lose oncogene addiction