Gene therapies offer new possibilities for the precise correction of monogenic disorders. Here, we present the first prime editing (PE)-based gene repair strategy for pathogenic COL17A1 variants that cause junctional epidermolysis bullosa (JEB). Type XVII collagen (C17), encoded by COL17A1, plays a critical role in skin aging, regeneration, and the maintenance of epidermal stem cell integrity. Treatment of primary human JEB keratinocytes with PE mRNAs resulted in COL17A1 editing efficiencies of up to 60% in bulk-treated cells, leading to the restoration of full-length, accurately shed C17. Chromosomal aberrations analysis by single targeted linker-mediated PCR sequencing analysis of gene-edited JEB keratinocytes confirmed the absence of unintended chromosomal rearrangements at potential off-target sites and only minimal on-target aberrations. Remarkably, in a xenograft model, in which C17+ cells represented only 55.9% of the input population, COL17A1-corrected cells populated 92.2% of the basal keratinocyte layer in the resulting skin grafts after 6 weeks. These observations highlight a potential selective advantage imparted by C17 restoration, in line with its canonical role in anchoring hemidesmosomes to the basement membrane and preserving the structural integrity of the interfollicular epidermal stem cell niche. Based on our results, we envision PE as an efficient and safe option to restore gene function in EB and other genodermatoses.

BACKGROUND:While most cutaneous squamous cell carcinomas (cSCCs) are treatable, certain high-risk cSCCs, such as those in recessive dystrophic epidermolysis bullosa (RDEB) patients, are particularly aggressive. Owing to repeated wounding, inflammation and unproductive healing, RDEB patients have a 68% cumulative risk of developing life-threatening cSCCs by the age of 35, and a 70% risk of death by the age of 45. Despite aggressive treatment, cSCC represents the leading cause of premature mortality in these patients, highlighting an unmet clinical need. Increasing evidence points to a role of altered metabolism in the initiation and maintenance of cSCC, making metabolism a potential therapeutic target.OBJECTIVES:We sought to determine the feasibility of targeting tumour cell energetics as a strategy to selectively hinder the growth advantage of aggressive cSCC.METHODS:We evaluated the cell energetics profiles of RDEB-SCC cells by analysing available gene expression data against multiple gene signatures and single-gene targets linked to metabolic reprogramming. Additionally, we employed real-time metabolic profiling to measure glycolysis and respiration in these cells. Furthermore, we investigated the anti-neoplastic properties of the metformin against human and murine high-risk cSCCs in vitro and in vivo.RESULTS:Gene expression analyses highlighted a divergence in cell energetics profiles between RDEB-SCC and non-malignant RDEB keratinocytes, with tumour cells demonstrating enhanced respiration and glycolysis scores. Real-time metabolic profiling supported these data and additionally highlighted a metabolic plasticity of RDEB-SCC cells. Against this background, metformin exerted an anti-neoplastic potential by hampering both respiration and glycolysis, and by inhibiting proliferation in vitro. Metformin treatment in an analogous model of fast-growing murine cSCC resulted in delayed tumour onset and slower tumour growth, translating to a 29% increase in median overall survival.CONCLUSIONS:Our data indicate that metformin exerts anti-neoplastic properties in aggressive cSCCs that exhibit high-risk features by interfering with respiration and glycolytic processes.

Antisense oligonucleotides (ASOs) represent an emerging therapeutic platform for targeting genetic diseases by influencing various aspects of (pre-)mRNA biology, such as splicing, stability, and translation. In this study, we investigated the potential of modulating the splicing pattern in recessive dystrophic epidermolysis bullosa (RDEB) patient cells carrying a frequent genomic variant (c.425A > G) that disrupts splicing in the COL7A1 gene by using short 2′-O-(2-Methoxyethyl) oligoribo-nucleotides (2′-MOE ASOs). COL7A1-encoded type VII collagen (C7) forms the anchoring fibrils within the skin that are essential for the attachment of the epidermis to the underlying dermis. As such, gene variants of COL7A1 leading to functionally impaired or absent C7 manifest in the form of extensive blistering and wounding. The severity of the disease pattern warrants the development of novel therapies for patients. The c.425A > G variant at the COL7A1 exon 3/intron 3 junction lowers the efficiency of splicing at this junction, resulting in non-functional C7 transcripts. However, we found that correct splicing still occurs, albeit at a very low level, highlighting an opportunity for intervention by modulating the splicing reaction. We therefore screened 2′-MOE ASOs that bind along the COL7A1 target region ranging from exon 3 to the intron 3/exon 4 junction for their ability to modulate splicing. We identified ASOs capable of increasing the relative levels of correctly spliced COL7A1 transcripts by RT-PCR, sqRT-PCR, and ddPCR. Furthermore, RDEB-derived skin equivalents treated with one of the most promising ASOs exhibited an increase in full-length C7 expression and its accurate deposition along the basement membrane zone (BMZ).

Staphylococcus aureus (S. aureus) typically colonizes human skin without clinical manifestations, but establishes a pathogenic infection when normal tissue function is compromised. Adaptation of S. aureus to the host niche requires a network of regulators and virulence factors, with long-term infection potentially contributing to wound chronification and skin cancer development. Given the observation of reduced microbial diversity in the wounds of patients suffering from recessive dystrophic epidermolysis bullosa (RDEB) with an increased abundance of S. aureus species, we aimed to characterize S. aureus isolates established from two different patients (SA2a and SA6) and assess their impact on keratinocytes. Based on RNAseq analysis we observed differences in the expression profile of virulence genes, such as enterotoxins, leukocidins and serine proteases, between the two isolates. In this context, we also found that the two S. aureus isolates also showed different impact on host cells, with SA6 exhibiting significantly higher infection potential and increased toxicity towards patient-derived keratinocytes compared to SA2a. Notably, changes to host cell transcriptome upon live infection with SA6 were associated with pathways involved in immune response and cell death, whereas those with SA2a were not. Taken together, our results highlight differences in the expression of distinct virulence factors between patient-derived S. aureus isolates that can account for differences in host cell responses, in turn potentially impacting clinical outcomes.

Conventional anti-cancer therapies based on chemo- and/or radiotherapy represent highly effective means to kill cancer cells but lack tumor specificity and, therefore, result in a wide range of iatrogenic effects. A promising approach to overcome this obstacle is spliceosome-mediated RNA trans-splicing (SMaRT), which can be leveraged to target tumor cells while leaving normal cells unharmed. Notably, a previously established RNA trans-splicing molecule (RTM44) showed efficacy and specificity in exchanging the coding sequence of a cancer target gene (Ct-SLCO1B3) with the suicide gene HSV1-thymidine kinase in a colorectal cancer model, thereby rendering tumor cells sensitive to the prodrug ganciclovir (GCV). In the present work, we expand the application of this approach, using the same RTM44 in aggressive skin cancer arising in the rare genetic skin disease recessive dystrophic epidermolysis bullosa (RDEB). Stable expression of RTM44, but not a splicing-deficient control (NC), in RDEB-SCC cells resulted in expression of the expected fusion product at the mRNA and protein level. Importantly, systemic GCV treatment of mice bearing RTM44-expressing cancer cells resulted in a significant reduction in tumor volume and weight compared with controls. Thus, our results demonstrate the applicability of RTM44-mediated targeting of the cancer gene Ct-SLCO1B3 in a different malignancy.

Viral antigens are among the strongest elicitors of immune responses. A significant proportion of the human population already carries pre-existing immunity against several childhood viruses, which could potentially be leveraged to fight cancer. We sought to provide proof of concept in mouse models that a pre-existing measles virus (MeV) immunity can be redirected to inhibit tumor growth by directly forcing expression of cognate antigens in the tumor. To this end, we designed DNA vaccines against known MeV cytotoxic and helper T epitopes, and administered these intradermally to mice that were subsequently challenged with syngeneic squamous cancer cells engineered to either express the cognate antigens or not. Alternatively, established wild-type tumors in vaccinated animals were treated intratumorally with in vitro transcribed mRNA encoding the cognate epitopes. Vaccination generated MeV cytotoxic T lymphocyte (CTL) immunity in mice as demonstrated by enhanced interferon gamma production, antigen-specific T cell proliferation, and CTL-mediated specific killing of antigen-pulsed target cells. When challenged with syngeneic tumor cells engineered to express the cognate antigens, 77% of MeV-vaccinated mice rejected the tumor versus 21% in control cohorts. Antitumor responses were largely dependent on the presence of CD8+ cells. Significant protection was observed even when only 25% of the tumor bulk expressed cognate antigens. We therefore tested the strategy therapeutically, allowing tumors to develop in vaccinated mice before intratumoral injection with Viromer nanoparticles complexed with mRNA encoding the cognate antigens. Treatment significantly enhanced overall survival compared with controls, including complete tumor regression in 25% of mice. Our results indicate that redirecting pre-existing viral immunity to fight cancer is a viable alternative that could meaningfully complement current cancer immune therapies such as personalized cancer vaccines and checkpoint inhibitor blockade.

Recessive dystrophic epidermolysis bullosa (RDEB) is a severe genetic skin blistering disease caused by defects in type VII collagen, required for the functional integrity of the dermo-epidermal junction. Owing to repeated cycles of wounding and infection/inflammation, RDEB patients have a high risk of developing aggressive squamous cell carcinoma (RDEB-SCC), which is the primary cause of premature mortality in these patients. The near-certainty of cancer development in these patients warrants the development of strategies to treat and prevent SCC development. Metformin is an anti-diabetic drug whose use has been associated with reduced risk of cancer development and improvement in overall cancer survival rates. As such, several clinical studies are underway to investigate its potential in cancer prevention. Here we investigate the use of metformin against the growth of human and murine SCC both in vitro and in vivo. Metformin inhibited the size of tumor colonies in clonogenicity assays and further demonstrated anti-proliferative effects against several human RDEB-SCC lines and the murine SCC VII line in vitro. In vivo, treatment with metformin resulted in a small yet significant delay in the time to development of visible tumors, as well as in a reduced growth rate of the tumors, leading to a significant increase in overall survival. Taken together further investigation into pathways impacted by metformin in SCC are indicated in order to evaluate the efficacy of this strategy against RDEB-SCC.