Decreased cytotoxic T cells and TCR clonality in organ transplant recipients with squamous cell carcinoma

Unraveling the landscape of non-melanoma skin cancer through single-cell RNA sequencing technology

Non-melanoma skin cancer (NMSC) mainly includes basal cell carcinoma, cutaneous squamous cell carcinoma, and Merkel cell carcinoma, showing a low mortality rate but the highest incidence worldwide. In recent decades, research has focused on understanding the pathogenesis and clinical treatments of NMSC, leading to significant advances in our knowledge of these diseases and the development of novel therapies, including immunotherapy. Nevertheless, the low to moderate objective response rate, high recurrence, and therapeutic resistance remain persistent challenges, which are partly attributable to the intratumoral heterogeneity. This heterogeneity indicates that tumor cells, immune cells, and stromal cells in the tumor microenvironment can be reshaped to a series of phenotypic and transcriptional cell states that vary in invasiveness and treatment responsiveness. The advent of single-cell RNA sequencing (scRNA-seq) has enabled the comprehensive profiling of gene expression heterogeneity at the single-cell level, which has been applied to NMSC to quantify cell compositions, define states, understand tumor evolution, and discern drug resistance. In this review, we highlight the key findings, with a focus on intratumoral heterogeneity and the mechanism of drug resistance in NMSC, as revealed by scRNA-seq. Furthermore, we propose potential avenues for future research in NMSC using scRNA-seq.

Immune Checkpoints and Cellular Landscape of the Tumor Microenvironment in Non-Melanoma Skin Cancer (NMSC)

Non-melanoma skin cancer (NMSC) is primarily categorized into basal cell carcinoma (BCC), the most prevalent form of skin cancer, and cutaneous squamous cell carcinoma (cSCC), the second most common type. Both BCC and cSCC represent a significant health burden, particularly in immunocompromised individuals and the elderly. The immune system plays a pivotal role in the development and progression of NMSC, making it a critical focus for therapeutic interventions. This review highlights key immunological targets in BCC and cSCC, with a focus on immune checkpoint molecules such as PD-1/PD-L1 and CTLA-4, which regulate T cell activity and contribute to immune evasion. This review also highlights anti-tumor immune cell subsets within the tumor microenvironment (TME), such as tumor-infiltrating lymphocytes (TILs) and dendritic cells. Additionally, it examines the immunosuppressive elements of the TME, including regulatory T cells (Tregs), myeloid-derived suppressor cells (MDSCs), tumor-associated macrophages (TAMs), and cancer-associated fibroblasts (CAFs), as well as their roles in NMSC progression and resistance to therapy. Emerging strategies targeting these immune elements, such as monoclonal antibodies, are also discussed for their potential to enhance anti-tumor immune responses and improve clinical outcomes. By elucidating the immunological landscape of BCC and cSCC and drawing comparisons to melanoma, this review highlights the transformative potential of immunotherapy in treating these malignancies.

Current Advances and Challenges in the Management of Cutaneous Squamous Cell Carcinoma in Immunosuppressed Patients

Cutaneous squamous cell carcinoma (cSCC) is the second most common skin malignancy and poses a significant risk to immunosuppressed patients, such as solid organ transplant recipients and those with hematopoietic malignancies, who are up to 100 times more likely to develop cSCC compared with the general population. This review summarizes the current state of treatment for cSCC in immunosuppressed patients, focusing on prevention, prophylaxis, surgical and non-surgical treatments, and emerging therapies. Preventative measures, including high-SPF sunscreen and prophylactic retinoids, are crucial for reducing cSCC incidence in these patients. Adjusting immunosuppressive regimens, particularly favoring mTOR inhibitors over calcineurin inhibitors, has been shown to lower cSCC risk. Surgical excision and Mohs micrographic surgery remain the primary treatments, with adjuvant radiation therapy recommended for high-risk cases. Traditional chemotherapy and targeted therapies like EGFR inhibitors have been utilized, though their efficacy varies. Immunotherapy, particularly with agents like cemiplimab and pembrolizumab, has shown promise, but its use in immunosuppressed patients requires further investigation due to potential risks of organ rejection and exacerbation of underlying conditions. Treatment of cSCC in immunosuppressed patients is multifaceted, involving preventive strategies, tailored surgical approaches, and cautious use of systemic therapies. While immunotherapy has emerged as a promising option, its application in immunosuppressed populations necessitates further research to optimize safety and efficacy. Future studies should focus on the integration of personalized medicine and combination therapies to improve outcomes for this vulnerable patient group.

Cutaneous Squamous Cell Carcinoma in Patients with Solid-Organ-Transplant-Associated Immunosuppression

The management of advanced cutaneous squamous cell carcinoma (CSCC) has been revolutionized by the introduction of immunotherapy. Yet, successful treatment with immunotherapy relies on an adequate antitumor immune response. Patients who are solid-organ transplant recipients (SOTRs) have a higher incidence of CSCC compared to the general population. This review discusses the current knowledge of epidemiology, pathophysiology, and management of patients with CSCC who are immunocompromised because of their chronic exposure to immunosuppressive medications to prevent allograft rejection. First, we discuss the prognostic impact of immunosuppression in patients with CSCC. Next, we review the risk of CSCC development in immunosuppressed patients due to SOT. In addition, we provide an overview of the biological immune disruption present in transplanted immunosuppressed CSCC patients. We discuss the available evidence on the use of immunotherapy and provide a framework for the management approach with SOTRs with CSCC. Finally, we discuss potential novel approaches that are being investigated for the management of immunosuppressed patients with CSCC.

The Mutational and Microenvironmental Landscape of Cutaneous Squamous Cell Carcinoma: A Review

Cutaneous squamous cell carcinoma (cSCC) manifests through the complex interactions of UV-induced DNA damage, genetic mutations, and alterations in the tumor microenvironment. A high mutational burden is present in cSCC, as well as both cSCC precursors and normal skin, making driver genes difficult to differentiate. Despite this, several key driver genes have been identified, including TP53, the NOTCH family, CDKN2A, PIK3CA, and EGFR. In addition to mutations, the tumor microenvironment and the manipulation and evasion of the immune system play a critical role in cSCC progression. Novel therapeutic approaches, such as immunotherapy and EGFR inhibitors, have been used to target these dysregulations, and have shown promise in treating advanced cSCC cases, emphasizing the need for targeted interventions considering both genetic and microenvironmental factors for improved patient outcomes.

How Can Spatial Transcriptomic Profiling Advance Our Understanding of Skin Diseases?

Spatial transcriptomic (ST) profiling is the mapping of gene expression within cell populations with preservation of positional context and represents an exciting new approach to develop our understanding of local and regional influences upon skin biology in health and disease. With the ability to probe from a few hundred transcripts to the entire transcriptome, multiple ST approaches are now widely available. In this paper, we review the ST field and discuss its application to dermatology. Its potential to advance our understanding of skin biology in health and disease is highlighted through the illustrative examples of 3 research areas: cutaneous aging, tumorigenesis, and psoriasis.

Single-Cell RNA Sequencing in Organ and Cell Transplantation

Single-cell RNA sequencing is a high-throughput novel method that provides transcriptional profiling of individual cells within biological samples. This method typically uses microfluidics systems to uncover the complex intercellular communication networks and biological pathways buried within highly heterogeneous cell populations in tissues. One important application of this technology sits in the fields of organ and stem cell transplantation, where complications such as graft rejection and other post-transplantation life-threatening issues may occur. In this review, we first focus on research in which single-cell RNA sequencing is used to study the transcriptional profile of transplanted tissues. This technology enables the analysis of the donor and recipient cells and identifies cell types and states associated with transplant complications and pathologies. We also review the use of single-cell RNA sequencing in stem cell implantation. This method enables studying the heterogeneity of normal and pathological stem cells and the heterogeneity in cell populations. With their remarkably rapid pace, the single-cell RNA sequencing methodologies will potentially result in breakthroughs in clinical transplantation in the coming years.

Skin cancer prevention - Recent advances and unmet challenges

Cutaneous squamous cell carcinoma (cSCC) is the second most common malignancy in the world. Among many identified risk factors, immunosuppression is a major factor that contributes to cSCC development. Organ transplant recipients (OTRs) are at markedly increased risk of developing multiple cSCCs with a propensity for advanced metastatic disease, leading to significant morbidity and mortality. The severity of the cSCC phenotype in OTRs highlights the urgent need to identify effective preventive modalities in this population. Despite recent advances in skin cancer prevention (e.g., nicotinamide) and treatment (e.g., immune checkpoint blockade), these modalities have limited utility in OTRs due to the lack of efficacy or significant side effect. Topical treatments against precancerous skin lesions, actinic keratosis (AK), remain the primary strategy to prevent cSCC in OTRs, which also have significant deficiencies in this population. Herein, we review the epidemiology, risk factors, and current cSCC prevention strategies. We highlight the gaps and future clinical strategies to address cSCC risk in high-risk populations.

Functional heterogeneity of human skin-resident memory T cells in health and disease

The human skin is populated by a diverse pool of memory T cells, which can act rapidly in response to pathogens and cancer antigens. Tissue-resident memory T cells (TRM ) have been implicated in range of allergic, autoimmune and inflammatory skin diseases. Clonal expansion of cells with TRM properties is also known to contribute to cutaneous T-cell lymphoma. Here, we review the heterogeneous phenotypes, transcriptional programs, and effector functions of skin TRM . We summarize recent studies on TRM formation, longevity, plasticity, and retrograde migration and contextualize the findings to skin TRM and their role in maintaining skin homeostasis and altered functions in skin disease.

Immunosenescence and Skin: A State of Art of Its Etiopathogenetic Role and Crucial Watershed for Systemic Implications

Immunosenescence is a complex multifactorial phenomenon consisting of wide-ranging remodeling of the immune system during the life span, resulting in an age-related qualitative-quantitative decline of immune cells and cytokines. A growing body of evidence in the international literature is highlighting the etiopathogenetic role of skin immunosenescence in the onset of various dermatologic conditions. Skin immunosenescence also serves as an interesting watershed for the onset of system-wide conditions in the context of allergic inflammation. Moreover, in recent years, an increasingly emerging and fascinating etiopathogenetic parallelism has been observed between some mechanisms of immunosenescence, both at cutaneous and systemic sites. This would help to explain the occurrence of apparently unconnected comorbidities. Throughout our review, we aim to shed light on emerging immunosenescent mechanisms shared between dermatologic disorders and other organ-specific diseases in the context of a more extensive discussion on the etiopathogenetic role of skin immunosenescence. A promising future perspective would be to focus on better understanding the mutual influence between skin and host immunity, as well as the influence of high inter-individual variability on immunosenescence/inflammaging. This can lead to a more comprehensive "immunobiographic" definition of each individual.

LINE-1 retrotransposon expression in cancerous, epithelial and neuronal cells revealed by 5' single-cell RNA-Seq

LINE-1 retrotransposons are sequences capable of copying themselves to new genomic loci via an RNA intermediate. New studies implicate LINE-1 in a range of diseases, especially in the context of aging, but without an accurate understanding of where and when LINE-1 is expressed, a full accounting of its role in health and disease is not possible. We therefore developed a method-5' scL1seq-that makes use of a widely available library preparation method (10x Genomics 5' single cell RNA-seq) to measure LINE-1 expression in tens of thousands of single cells. We recapitulated the known pattern of LINE-1 expression in tumors-present in cancer cells, absent from immune cells-and identified hitherto undescribed LINE-1 expression in human epithelial cells and mouse hippocampal neurons. In both cases, we saw a modest increase with age, supporting recent research connecting LINE-1 to age related diseases.

Molecular Alterations in Cutaneous Squamous Cell Carcinoma in Immunocompetent and Immunosuppressed Hosts-A Systematic Review

The characterization of cutaneous squamous cell carcinoma (cSCC) at the molecular level is lacking in the current literature due to the high mutational burden of this disease. Immunosuppressed patients afflicted with cSCC experience considerable morbidity and mortality. In this article, we review the molecular profile of cSCC among the immunosuppressed and immunocompetent populations at the genetic, epigenetic, transcriptomic, and proteometabolomic levels, as well as describing key differences in the tumor immune microenvironment between these two populations. We feature novel biomarkers from the recent literature which may serve as potential targets for therapy.

Human Regulatory T Cells: Understanding the Role of Tregs in Select Autoimmune Skin Diseases and Post-Transplant Nonmelanoma Skin Cancers

Regulatory T cells (Tregs) play an important role in maintaining immune tolerance and homeostasis by modulating how the immune system is activated. Several studies have documented the critical role of Tregs in suppressing the functions of effector T cells and antigen-presenting cells. Under certain conditions, Tregs can lose their suppressive capability, leading to a compromised immune system. For example, mutations in the Treg transcription factor, Forkhead box P3 (FOXP3), can drive the development of autoimmune diseases in multiple organs within the body. Furthermore, mutations leading to a reduction in the numbers of Tregs or a change in their function facilitate autoimmunity, whereas an overabundance can inhibit anti-tumor and anti-pathogen immunity. This review discusses the characteristics of Tregs and their mechanism of action in select autoimmune skin diseases, transplantation, and skin cancer. We also examine the potential of Tregs-based cellular therapies in autoimmunity.

The Tumor Immune Microenvironment in Cutaneous Squamous Cell Carcinoma Arising in Organ Transplant Recipients

Cutaneous squamous cell carcinoma (cSCC) is the most common malignancy in immune-suppressed organ transplant recipients (OTRs). Whilst rates of other malignancies (both cutaneous and non-cutaneous) are elevated in this population, the increase is far less striking. This suggests that cSCC must be a highly immunogenic tumor. The tumor immune microenvironment is altered in cSCC from OTRs. It has reduced anti-tumor properties and instead provides an environment that facilitates tumor growth and survival. Understanding the composition and function of the tumor immune microenvironment in cSCC from OTRs is useful for prognostication and therapeutic decisions.

Understanding the squamous cell carcinoma immune microenvironment

Primary cutaneous squamous cell carcinoma (cSCC) is the second most common human cancer with a rising incidence of about 1.8 million in the United States annually. Primary cSCC is usually curable by surgery; however, in some cases, cSCC eventuates in nodal metastasis and death from disease specific death. cSCC results in up to 15,000 deaths each year in the United States. Until recently, non-surgical options for treatment of locally advanced or metastatic cSCC were largely ineffective. With the advent of checkpoint inhibitor immunotherapy, including cemiplimab and pembrolizumab, response rates climbed to 50%, representing a vast improvement over chemotherapeutic agents used previously. Herein, we discuss the phenotype and function of SCC associated Langerhans cells, dendritic cells, macrophages, myeloid derived suppressor cells and T cells as well as SCC-associated lymphatics and blood vessels. Possible role(s) of SCC-associated cytokines in progression and invasion are reviewed. We also discuss the SCC immune microenvironment in the context of currently available and pipeline therapeutics.

Unravelling the landscape of skin cancer through single-cell transcriptomics

The human skin is a complex organ that forms the first line of defense against pathogens and external injury. It is composed of a wide variety of cells that work together to maintain homeostasis and prevent disease, such as skin cancer. The exponentially rising incidence of skin malignancies poses a growing public health challenge, particularly when the disease course is complicated by metastasis and therapeutic resistance. Recent advances in single-cell transcriptomics have provided a high-resolution view of gene expression heterogeneity that can be applied to skin cancers to define cell types and states, understand disease evolution, and develop new therapeutic concepts. This approach has been particularly valuable in characterizing the contribution of immune cells in skin cancer, an area of great clinical importance given the increasing use of immunotherapy in this setting. In this review, we highlight recent skin cancer studies utilizing bulk RNA sequencing, introduce various single-cell transcriptomics approaches, and summarize key findings obtained by applying single-cell transcriptomics to skin cancer.

Research progress on application of single-cell TCR/BCR sequencing technology to the tumor immune microenvironment, autoimmune diseases, and infectious diseases

Single-cell omics is the profiling of individual cells through sequencing and other technologies including high-throughput analysis for single-cell resolution, cell classification, and identification as well as time series analyses. Unlike multicellular studies, single-cell omics overcomes the problem of cellular heterogeneity. It provides new methods and perspectives for in-depth analyses of the behavior and mechanism of individual cells in the cell population and their relationship with the body, and plays an important role in basic research and precision medicine. Single-cell sequencing technologies mainly include single-cell transcriptome sequencing, single-cell assay for transposase accessible chromatin with high-throughput sequencing, single-cell immune profiling (single-cell T-cell receptor [TCR]/B-cell receptor [BCR] sequencing), and single-cell transcriptomics. Single-cell TCR/BCR sequencing can be used to obtain a large amount of single-cell gene expression and immunomics data at one time, and combined with transcriptome sequencing and TCR/BCR diversity data, can resolve immune cell heterogeneity. This paper summarizes the progress in applying single-cell TCR/BCR sequencing technology to the tumor immune microenvironment, autoimmune diseases, infectious diseases, immunotherapy, and chronic inflammatory diseases, and discusses its shortcomings and prospects for future application.

Single-cell entropy network detects the activity of immune cells based on ribosomal protein genes

We developed a new computational method, Single-Cell Entropy Network (SCEN) to analyze single-cell RNA-seq data, which used the information of gene-gene associations to discover new heterogeneity of immune cells as well as identify existing cell types. Based on SCEN, we defined association-entropy (AE) for each cell and each gene through single-cell gene co-expression networks to measure the strength of association between each gene and all other genes at a single-cell resolution. Analyses of public datasets indicated that the AE of ribosomal protein genes (RP genes) varied greatly even in the same cell type of immune cells and the average AE of RP genes of immune cells in each person was significantly associated with the healthy/disease state of this person. Based on existing research and theory, we inferred that the AE of RP genes represented the heterogeneity of ribosomes and reflected the activity of immune cells. We believe SCEN can provide more biological insights into the heterogeneity and diversity of immune cells, especially the change of immune cells in the diseases.

Research Progress of Cell Lineage Tracing and Single-Cell Sequencing Technology in Malignant Skin Tumors

Cell lineage tracing and single-cell sequencing have been widely applied in development biology and oncology to reveal the molecular mechanisms in multiple basic biological processes and the differentiation of stem cells, as well as quantify the differences between single cells. They provide new methods for in-depth understanding of the origin of tumors, the heterogeneity of tumor cells, and the drug resistance mechanism of tumors, thus inspiring new strategies for tumor treatment. In this review, we summarized the progress of cell lineage tracing technology and single-cell sequencing technology in the research of malignant melanoma and cutaneous squamous cell carcinoma, attempting to spark new ideas for further research on skin tumors.

Cutaneous squamous cell carcinoma arising in immunosuppressed patients: a systematic review of tumor profiling studies

As solid organ transplantation becomes more prevalent, more individuals are living as members of the immunosuppressed population with an elevated risk for cutaneous squamous cell carcinoma (cSCC). Although great progress has been made in understanding the pathogenesis of cSCC in general, little is known about the drivers of tumorigenesis in immunosuppressed patients and organ-transplant recipients, specifically. This systematic review sought to synthesize information regarding the genetic and epigenetic alterations as well as changes in protein and mRNA expression that place this growing population at risk for cSCC, influence treatment response, and promote tumor aggressiveness. This review will provide investigators with a framework to identify future areas of investigation and clinicians with additional insight into how to best manage these patients.

Cutaneous Squamous Cell Carcinoma: The Frontier of Cancer Immunoprevention

Cutaneous squamous cell carcinoma (cSCC) is the second most common cancer, with its incidence rising steeply. Immunosuppression is a well-established risk factor for cSCC, and this risk factor highlights the critical role of the immune system in regulating cSCC development and progression. Further highlighting the nature of cSCC as an immunological disorder, substantial evidence demonstrates a tight association between cSCC risk and age-related immunosenescence. Besides the proven efficacy of immune checkpoint blockade therapy for advanced cSCC, novel immunotherapy that targets cSCC precursor lesions has shown efficacy for cSCC prevention. Furthermore, the appreciation of the interplay between keratinocytes, commensal papillomaviruses, and the immune system has revealed the possibility for the development of a preventive cSCC vaccine. cSCC shares fundamental aspects of its origin and pathogenesis with mucosal SCCs. Therefore, advances in the field of cSCC immunoprevention will inform our approach to the management of mucosal SCCs and potentially other epithelial cancers.

Clinicopathologic analysis of malignant or premalignant cutaneous neoplasms in Japanese kidney transplant recipients

It is well known that recipients of kidney transplants are at an increased risk of developing malignant or premalignant cutaneous neoplasms (MPCNs) after transplantation. However, the pathogenesis of MPCNs after kidney transplant has not been well-studied in Asian populations. This study aimed to describe the clinicopathologiccharacteristics of MPCNs in an Asian population. We retrospectively reviewed the medical records of 1956 patients who received kidney transplants at two hospitals in Japan, between 2003 and 2019. Among these patients, 24 developed 50 MPCN lesions, including 14 squamous cell carcinoma (SCC, 28%), 23 Bowen's disease (BD, 46%), 11 actinic keratosis (AK, 22%), and two basal cell carcinoma (BCC, 4%). No patient had malignant melanoma. The duration from transplantation to the diagnosis was significantly longer for SCC than for BD or AK (P=0.021, 0.036, respectively). Seven patients had multiple MPCNs in sun-exposed areas of skin. Among the 50 MPCNs, 40 (80%) were located in sun-exposed areas, and 10 (20%) were located in sun-protected areas. MPCNs in sun-exposed skin were frequently accompanied by dermal solar elastosis (90%, 36/40). We found high-risk human papillomavirus (HR-HPV) infections in two anogenital lesions (100%, 2/2). In contrast, HR-HPV infections were not detected in any extragenital lesions (0%, 0/30). Our results suggested that, among Japanese recipients of kidney transplant, MPCNs in sun-exposed skin areas may be associated with immunosuppression and ultraviolet exposure.

Progressive Cellular Senescence Mediates Renal Dysfunction in Ischemic Nephropathy

BACKGROUND

Peripheral vascular diseases may induce chronic ischemia and cellular injury distal to the arterial obstruction. Cellular senescence involves proliferation arrest in response to stress, which can damage neighboring cells. Renal artery stenosis (RAS) induces stenotic-kidney dysfunction and injury, but whether these arise from cellular senescenceand their temporal pattern remain unknown.

METHODS

Chronic renal ischemia was induced in transgenic INK-ATTAC and wild type C57BL/6 mice by unilateral RAS, and kidney function (in vivo micro-MRI) and tissue damage were assessed. Mouse healthy and stenotic kidneys were analyzed using unbiased single-cell RNA-sequencing. To demonstrate translational relevance, cellular senescence was studied in human stenotic kidneys.

RESULTS

Using intraperitoneal AP20187 injections starting 1, 2, or 4 weeks after RAS, selective clearance of cells highly expressing p16^Ink4a attenuated cellular senescence and improved stenotic-kidney function; however, starting treatment immediately after RAS induction was unsuccessful. Broader clearance of senescent cells, using the oral senolytic combination dasatinib and quercetin, in C57BL/6 RAS mice was more effective in clearing cells positive for p21 (Cdkn1a) and alleviating renal dysfunction and damage. Unbiased, single-cell RNA sequencing in freshly dissociated cells from healthy and stenotic mouse kidneys identified stenotic-kidney epithelial cells undergoing both mesenchymal transition and senescence. As in mice, injured human stenotic kidneys exhibited cellular senescence, suggesting this process is conserved.

CONCLUSIONS

Maladaptive tubular cell senescence, involving upregulated p16 (Cdkn2a), p19 (Cdkn2d), and p21 (Cdkn1a) expression, is associated with renal dysfunction and injury in chronic ischemia. These findings support development of senolytic strategies to delay chronic ischemic renal injury.

Delayed Response After Confirmed Progression (DR) and Other Unique Immunotherapy-Related Treatment Concepts in Cutaneous Squamous Cell Carcinoma

Non-melanoma skin cancers are one of the most common cancers diagnosed worldwide, with the highest incidence in Australia and New Zealand. Systemic treatment of locally advanced and metastatic cutaneous squamous cell carcinomas has been revolutionized by immune checkpoint inhibition with PD-1 blockade. We highlight treatment issues distinct to the management of the disease including expansion of the traditional concept of pseudoprogression and describe delayed responses after immune-specific response criteria confirmed progressive disease with and without clinical deterioration. We term this phenomenon “delayed response after confirmed progression (DR)”. We also discuss the common development of second primary tumors, heterogeneous disease responses, and expanding clinical boundaries for immunotherapy use.