Revertant Mosaicism in Genodermatoses: Natural Gene Therapy Right before Your Eyes

Epithelial competition determines gene therapy potential to suppress Fanconi Anemia oral cancer risk

Fanconi Anemia (FA) is a heritable syndrome characterized by DNA damage repair deficits, frequent malformations and a significantly elevated risk of bone marrow failure, leukemia, and mucosal head and neck squamous cell carcinomas (HNSCC). Hematopoietic stem cell gene therapy can prevent marrow failure and lower leukemia risk, but mucosal gene therapy to lower HNSCC risk remains untested. Major knowledge gaps include an incomplete understanding of how rapidly gene-corrected cellular lineages could spread through the oral epithelium, and which delivery parameters are critical for ensuring efficient gene correction. To answer these questions, we extended an agent-based model of the oral epithelium to include the delivery of gene correction in situ to FA cells and the competitive dynamics between cellular lineages with and without gene correction. We found that only gene-corrected lineages with substantial proliferative advantages (probability of resisting displacement out of the basal layer ≥ 0.1) could spread on clinically relevant timelines, and that these lineages were initially at high risk of loss in the generations following correction. Delivering gene correction to many cells minimizes the risk of loss, while delivery to many distinct locations within a tissue maximizes the rate of spread. To determine the impact of mucosal gene therapy in preventing the clonal expansion of pre-cancerous mutations, we compared the expected burden of T P 53 mutations in simulated tissue sections with and without gene correction. We found that when FA cells have elevated genome instability or a T P 53 -dependent proliferative advantage, gene correction can substantially reduce the accumulation of pro-tumorigenic mutations. This model illustrates the power of computational frameworks to identify critical determinants of therapeutic success to enable experimental optimization and support novel and effective gene therapy applications.

Treatment of Epidermolysis Bullosa and Future Directions: A Review

Epidermolysis bullosa (EB) comprises rare genetic disorders characterized by skin and mucosal membrane blistering induced by mechanical trauma. Molecularly, pathogenic variants affect genes encoding proteins crucial for epidermal-dermal adhesion and stability. Management of severe EB is multidisciplinary, focusing on wound healing support, ensuring that patients thrive, and complication treatment. Despite extensive research over 30 years, novel therapeutic approaches face challenges. Gene therapy and protein therapy struggle with efficacy, while regenerative cell-based therapies show limited effects. Drug repurposing to target various pathogenic mechanisms has gained attention, as has in vivo gene therapy with drugs for dystrophic and junctional EB that were recently approved by the US Food and Drug Administration (FDA) and European Medicines Agency (EMA). However, their high cost limits global accessibility. This review examines therapeutic advancements made over the past 5 years, exploiting a systematic literature review and clinical trial data.

Tissue mosaicism following stem cell aging: blood as an exemplar

Loss of stem cell regenerative potential underlies aging of all tissues. Somatic mosaicism, the emergence of cellular patchworks within tissues, increases with age and has been observed in every organ yet examined. In the hematopoietic system, as in most tissues, stem cell aging through a variety of mechanisms occurs in lockstep with the emergence of somatic mosaicism. Here, we draw on insights from aging hematopoiesis to illustrate fundamental principles of stem cell aging and somatic mosaicism. We describe the generalizable changes intrinsic to aged stem cells and their milieu that provide the backdrop for somatic mosaicism to emerge. We discuss genetic and nongenetic mechanisms that can result in tissue somatic mosaicism and existing methodologies to detect such clonal outgrowths. Finally, we propose potential avenues to modify mosaicism during aging, with the ultimate aim of increasing tissue resiliency.

Emerging Gene Therapeutics for Epidermolysis Bullosa under Development

The monogenetic disease epidermolysis bullosa (EB) is characterised by the formation of extended blisters and lesions on the patient's skin upon minimal mechanical stress. Causal for this severe condition are genetic mutations in genes, leading to the functional impairment, reduction, or absence of the encoded protein within the skin's basement membrane zone connecting the epidermis to the underlying dermis. The major burden of affected families justifies the development of long-lasting and curative therapies operating at the genomic level. The landscape of causal therapies for EB is steadily expanding due to recent breakthroughs in the gene therapy field, providing promising outcomes for patients suffering from this severe disease. Currently, two gene therapeutic approaches show promise for EB. The clinically more advanced gene replacement strategy was successfully applied in severe EB forms, leading to a ground-breaking in vivo gene therapy product named beremagene geperpavec (B-VEC) recently approved from the US Food and Drug Administration (FDA). In addition, the continuous innovations in both designer nucleases and gene editing technologies enable the efficient and potentially safe repair of mutations in EB in a potentially permanent manner, inspiring researchers in the field to define and reach new milestones in the therapy of EB.

Effects of TP63 mutations on keratinocyte adhesion and migration

The goal of this study was to investigate the molecular mechanisms responsible for the formation of skin erosions in patients affected by Ankyloblepharon-ectodermal defects-cleft lip/palate syndrome (AEC). This ectodermal dysplasia is caused by mutations in the TP63 gene, which encodes several transcription factors that control epidermal development and homeostasis. We generated induced pluripotent stem cells (iPSC) from AEC patients and corrected the TP63 mutations using genome editing tools. Three pairs of the resulting conisogenic iPSC lines were differentiated into keratinocytes (iPSC-K). We identified a significant downregulation of key components of hemidesmosomes and focal adhesions in AEC iPSC-K compared to their gene-corrected counterparts. Further, we demonstrated reduced AEC iPSC-K migration, suggesting the possibility that a process critical for cutaneous wound healing might be impaired in AEC patients. Next, we generated chimeric mice expressing a TP63-AEC transgene and confirmed a downregulation of these genes in transgene-expressing cells in vivo. Finally, we also observed these abnormalities in AEC patient skin. Our findings suggest that integrin defects in AEC patients might weaken the adhesion of keratinocytes to the basement membrane. We propose that reduced expression of extracellular matrix adhesion receptors, potentially in conjunction with previously identified desmosomal protein defects, contribute to skin erosions in AEC.

Effects of TP63 Mutations on Keratinocyte Adhesion and Migration

The goal of this study was to investigate the molecular mechanisms responsible for the formation of skin erosions in patients affected by Ankyloblepharon-ectodermal defects-cleft lip/palate syndrome (AEC). This ectodermal dysplasia is caused by mutations in the TP63 gene, which encodes several transcription factors that control epidermal development and homeostasis. We generated induced pluripotent stem cells (iPSC) from AEC patients and corrected the TP63 mutations using genome editing tools. Three pairs of the resulting conisogenic iPSC lines were differentiated into keratinocytes (iPSC-K). We identified a significant downregulation of key components of hemidesmosomes and focal adhesions in AEC iPSC-K compared to their gene-corrected counterparts. Further, we demonstrated reduced iPSC-K migration, suggesting the possibility that a process critical for cutaneous wound healing might be impaired in AEC patients. Next, we generated chimeric mice expressing a TP63-AEC transgene and confirmed a downregulation of these genes in transgene-expressing cells in vivo. Finally, we also observed these abnormalities in AEC patient skin. Our findings suggest that integrin defects in AEC patients might weaken the adhesion of keratinocytes to the basement membrane. We propose that reduced expression of extracellular matrix adhesion receptors, potentially in conjunction with previously identified desmosomal protein defects, contribute to skin erosions in AEC.

Inherited Reticulate Pigmentary Disorders

Reticulate pigmentary disorders (RPDs) are a group of inherited and acquired skin conditions characterized by hyperpigmented and/or hypopigmented macules. Inherited RPDs include dyschromatosis symmetrica hereditaria (DSH), dyschromatosis universalis hereditaria (DUH), reticulate acropigmentation of Kitamura (RAK), Dowling-Degos disease (DDD), dyskeratosis congenita (DKC), Naegeli-Franceschetti-Jadassohn syndrome (NFJS), dermatopathia pigmentosa reticularis (DPR), and X-linked reticulate pigmentary disorder. Although reticulate pattern of pigmentation is a common characteristic of this spectrum of disorders, the distribution of pigmentation varies among these disorders, and there may be clinical manifestations beyond pigmentation. DSH, DUH, and RAK are mostly reported in East Asian ethnicities. DDD is more common in Caucasians, although it is also reported in Asian countries. Other RPDs show no racial predilection. This article reviews the clinical, histological, and genetic variations of inherited RPDs.