The Chicken Embryo Model: A Novel and Relevant Model for Immune-Based Studies

A scientific case for revisiting the embryonic chicken model in biomedical research

The availability of fertilised chicken eggs and the accessibility and rapid development of the avian embryo, have been utilised in biomedical scientific research to make fundamental discoveries including of developmental processes that are common to all vertebrates, advances in teratology, the understanding of tumour growth and metastasis, angiogenesis, cancer drug assessment and vaccine development as well as advances in understanding avian specific biology. However, recent innovations in chicken transgenesis, genome engineering and surrogate host technology in chickens have only been utilised in a few of these fields of research, specifically some areas of developmental biology, avian sex determination and immunology. To understand why other biomedical fields have not adopted modern chicken transgenic tools, we investigated the non-technical summaries of projects granted in the UK under the Animals (Scientific Procedures) Act 1986 between 2017 and 2023 to assess when and how chicken embryos are used in research, and if they were considered as a Replacement model for other species.

Genetic regulation of gene expression across multiple tissues in chickens

The chicken is a valuable model for understanding fundamental biology and vertebrate evolution and is a major global source of nutrient-dense and lean protein. Despite being the first non-mammalian amniote to have its genome sequenced, a systematic characterization of functional variation on the chicken genome remains lacking. Here, we integrated bulk RNA sequencing (RNA-seq) data from 7,015 samples, single-cell RNA-seq data from 127,598 cells and 2,869 whole-genome sequences to present a pilot atlas of regulatory variants across 28 chicken tissues. This atlas reveals millions of regulatory effects on primary expression (protein-coding genes, long non-coding RNA and exons) and post-transcriptional modifications (alternative splicing and 3'-untranslated region alternative polyadenylation). We highlighted distinct molecular mechanisms underlying these regulatory variants, their context-dependent behavior and their utility in interpreting genome-wide associations for 39 chicken complex traits. Finally, our comparative analyses of gene regulation between chickens and mammals demonstrate how this resource can facilitate cross-species gene mapping of complex traits.

Cellular landscape of avian intestinal organoids revealed by single cell transcriptomics

Studies of the avian gastrointestinal tract, where nutrient absorption and key host-pathogen interactions occur, have been strongly enabled by the development of intestinal organoid models. Here we report a single cell transcriptomic atlas of intestinal organoid cells derived from embryos of broiler and layer chickens, capturing mesenchymal, epithelial, endothelial, immune and neuronal cell lineages. Eight inferred mesenchymal subpopulations reflect anatomically distinct intestinal layers, including fibroblasts, telocytes, myofibroblasts, smooth myocytes, pericytes, and interstitial cells of Cajal. Identified heterogeneity within the epithelial lineage included enterocytes, goblet cells, Paneth cells, tuft cells, and diverse enteroendocrine cell subtypes. Additionally, we identified candidate macrophages, monocytes, γδ T cells, NK cells and granulocytes. Layer and broiler organoids showed significant differences in cell-specific transcriptome, most pronounced in epithelial cells, pointing to divergent selection on intestinal physiology. Our analysis finally provides a catalogue of novel cell marker genes to enable future research of chicken intestinal organoids.

The Chicken Embryo: An Alternative Animal Model in Development, Disease and Pharmacological Treatment

To examine various medications and substances, in vivo models such as rats and mice are routinely used. However, it is utterly desirable to reduce extensive amounts of animals for these experimental models, which are costly and time-consuming. Animals are frequently put through a variety of procedures that could cause them pain, distress, or even harm; therefore, it is important to think about the ethical ramifications of using them in research. Thus, by following the three R's of animal research: reduction, replacement, and refinement, living animals used in studies should be minimized. The embryo of Gallus gallus, the domestic chicken, is a great model to research many different diseases and conditions. Its efficient blood supply from the chorioallantoic membrane gives us a unique possibility to administer chemicals or cells to the embryo in a noninvasive manner. In this review, we evaluate some advantages and disadvantages of using the developing chicken as an alternative in vivo model for development, disease, and pharmacological treatment. We focus on the top two leading causes of death: neurological disorders and cancer. We present a number of studies that describe the use of the chicken embryo in neuroscience and neurodevelopment research, in cancer research, and pharmacodynamic and pharmacokinetic studies. These studies show that the chicken embryo is an inexpensive, readily available, self-sufficient model with a short incubation period, high accessibility, and ideal for drug screening, making it an appealing model that can provide insightful biological and pharmacological information.

Methodological and Ethical Considerations in the Use of Chordate Embryos in Biomedical Research

Animal embryos are vital tools in scientific research, providing insights into biological processes and disease mechanisms. This paper explores their historical and contemporary significance, highlighting the shift towards the refinement of in vitro systems as alternatives to animal experimentation. We have conducted a data review of the relevant literature on the use of embryos in research and synthesized the data to highlight the importance of this model for scientific progress and the ethical considerations and regulations surrounding embryo research, emphasizing the importance of minimizing animal suffering while promoting scientific progress through the principles of replacement, reduction, and refinement. Embryos from a wide range of species, including mammals, fish, birds, amphibians, and reptiles, play a crucial experimental role in enabling us to understand factors such as substance toxicity, embryonic development, metabolic pathways, physiological processes, etc., that contribute to the advancement of the biological sciences. To apply this model effectively, it is essential to match the research objectives with the most appropriate methodology, ensuring that the chosen approach is appropriate for the scope of the study.

Evaluation of tumor-colonizing Salmonella strains using the chick chorioallantoic membrane model

The chick embryo chorioallantoic membrane (CAM) tumor model is a valuable preclinical model for studying the tumor-colonizing process of Salmonella enterica serovar Typhimurium. It offers advantages such as cost-effectiveness, rapid turnaround, reduced engraftment issues, and ease of observation. In this study, we explored and validated the applicability of the partially immune-deficient CAM tumor model. Herein, we demonstrate that Salmonella preferentially colonizes tumors and directly causes tumor cell death. Bacterial migration, tumor colonization, and intra-tumor distribution did not require flagellar-mediated motility. The vast majority of Salmonella that colonized the CAM tumor were extracellular. Thus, tumor invasion was independent of both Salmonella pathogenicity island-1-encoded and Salmonella pathogenicity island-2-encoded type III secretion systems. Surprisingly, the extracellular residence of Salmonella on CAM tumors did not require biofilm formation. We evaluated our wild-type parental strain compared to the attenuated clinical strain VNP20009 and discovered a reduced tumor colonization capability of VNP20009. The inability to effectively colonize CAM tumors potentially explains the reduced anti-tumor efficacy of VNP20009. Our work establishes the xenograft CAM model as an informative and predictive screening platform for studying tumor-colonizing Salmonella.IMPORTANCECancer has a major impact on society, as it poses a significant health burden to human populations worldwide. Salmonella Typhimurium has demonstrated promise in cancer treatment by exerting direct tumoricidal effects and enhancing host-mediated anti-tumor immunity in xenograft mouse studies. A general understanding of its pathogenesis and the relative ease of genetic manipulation support the development of attenuated strains for therapeutic use. Alternative in ovo models, such as the chorioallantoic membrane tumor model, present a suitable screening platform to accelerate the development of therapeutic strains. It allows for rapid evaluation of Salmonella strains to assess their efficacy and potential as oncolytic agents. The present study establishes that the in ovo tumor model can be utilized as a preclinical tool for evaluating oncolytic Salmonella, bridging the gap between in vitro and in vivo screening.

The search to understand the development of the chicken immune system: Differences in expression of MHC class I loci and waves of thymocytes as evolutionary relics?

Chickens are renowned as a model for embryogenesis but have also been responsible for crucial advances in virology, cancer research and immunology. However, chickens are best known as a major source of animal protein for human nutrition, with roughly 80 billion chickens alive each year supplying meat and eggs, the vast majority part of a global poultry industry. As a result, avian immunology been studied intensively for over 60 years, and it has become clear that a major genetic locus in chickens determining resistance to infectious disease and response to vaccines is the major histocompatibility complex (MHC). Compared to typical mammals, the chicken MHC is compact and simple, with only two classical class I genes. A dominantly-expressed class I gene, BF2, is the major ligand for cytotoxic T lymphocytes (CTLs), while the other locus, BF1, is much less well-expressed, lacking in some MHC haplotypes, and is a ligand for natural killer (NK) cells. Cell surface class I expression in neonatal chicks is far less than in adults, and one possibility is that BF2 is not well-expressed early in ontogeny. A precedent is found for amphibians: the single classical class I molecule is not expressed in tadpoles of Xenopus frogs, although non-polymorphic (and thus non-classical) class I molecules from the XNC locus are expressed, which are recognised for immune defence by non-canonical NKT lymphocytes. Indeed, three waves of different T cells are produced by the Xenopus thymus: in tadpoles, during metamorphosis and finally as adults. Three waves of thymic emigrants are also found for chickens, and reasoning by analogy, it may be that the waves of thymocytes and the expression of class I molecules during ontogeny of chickens are evolutionary relics. As well as scientific interest in the ontogeny of MHC class I expression and appearance of peripheral T cells, there are potential practical implications, given the importance of vaccination in ovo and in day-old chicks for the poultry industry.

Development and Validation of a Minimally Invasive Transuterine Experimental Model of Gastroschisis

INTRODUCTION

Perinatal management of gastroschisis remains a subject of substantial research. Current models, including teratogenic, genetic, and surgical approaches, often fail to accurately replicate gastroschisis, exhibiting limitations such as inaccurate phenotyping, low success rates, high mortality, lack of scientific validation, and significant technical challenges. Refined disease models are essential for improving the understanding of GS. This study seeks to develop and validate a minimally invasive transuterine experimental model of GS that overcomes these existing constraints to advance gastroschisis research.

METHODS

A gastroschisis model was surgically created in rat fetuses at E17 (n = 51 fetuses from n = 13 dams). Intestines were harvested at term and divided into herniated gastroschisis (GS-H), intra-abdominal gastroschisis (GS-I), and control (Co) groups. Morphometric analysis, histopathological examination, immunohistochemistry for interstitial cells of Cajal (ICC), double immunofluorescence for ICC and mast cells, TUNEL assay for apoptotic cells, and multiplex cytokine assay were performed to assess intestinal architecture, inflammation, ICC network, apoptosis, and cytokine levels across studied groups.

RESULTS

Histology from GS intestines revealed subchronic inflammation, peel formation, and architectural disruption. Herniated intestines exhibited a significantly increased weight/length ratio and thicker outer layers (p < 0.001) compared with control intestines. Herniated intestines had elevated inflammatory cytokine levels (GS-H vs GS-I and Co, p < 0.05 for G-CSF, GM-CSF, IL-12p70, IL-1beta) and increased apoptotic activity.

CONCLUSIONS

We developed and validated a new surgical model of GS that offers improved survival and feasibility. The key morphological changes and molecular markers observed in this experimental model resemble human gastroschisis.

The chorioallantoic membrane (CAM) model: From its origins in developmental biology to its role in cancer research

Over the past century, the chick embryo model, historically employed for research in developmental biology, has become a valuable tool for cancer research. The characteristics of the chick chorioallantoic membrane (CAM) make it a convenient model for the study of cancer, leading to the establishment of the CAM assay as an alternative to traditional in vivo cancer models. In this review we will explore the characteristics of the CAM that make it suitable for cancer research, as well as its consolidation as a versatile platform in this field. We will put particular emphasis on describing the key features that make this model an important asset for studying the hallmarks of cancer and for testing a wide variety of therapeutic strategies for its treatment, and which make it a suitable host for patient-derived xenografts (PDX). Additionally, we will examine the wide spectrum of methodological approaches available to study these subjects, highlighting some innovative cases. Finally, we will discuss the advantages and disadvantages of the chick CAM as a model for cancer research and how we can improve this model to its full potential.

Patient-derived xenografts from circulating cancer stem cells as a preclinical model for personalized pancreatic cancer research

Patient-derived xenografts (PDXs) provide biologically relevant models and potential platforms for the development of treatment strategies for precision medicine in pancreatic cancer. Furthermore, circulating epithelial tumor cells (CETCs/CTCs) are released into the bloodstream by solid tumors and a rare subpopulation-circulating cancer stem cells (cCSCs) - is considered to be responsible for recurrence and plays a key role in metastasis. For the identification of cCSCs, an innovative in vitro assay to generate tumorspheres was established in this study. The number of tumorspheres and CETCs/CTCs was analyzed perioperatively in 25 pancreatic cancer patients. Additionally, an individual in vivo chorioallantoic membrane (CAM) culture system was used to generate PDXs from these tumorspheres. While overall correlations of CETCs/CTCs with clinicopathological parameters did not reach statistical significance, a significant difference in the number of tumorspheres was observed between patient subgroups with lower and higher UICC stages. This finding underscores their potential as biomarkers, providing valuable insights into clinical decision-making and tumor progression. The application of tumorspheres on the CAM successfully established PDXs within 7 days. These xenografts closely resembled the histological features of the primary tumor. Hence, this model represents a novel and fast option for individualized testing of new therapies for PDAC.

In ovo delivery of carvacrol triggers expression of chemotactic factors, antimicrobial peptides and pro-inflammatory pathways in the yolk sac of broiler chicken embryos

BACKGROUND

Broiler chickens are most vulnerable immediately after hatching due to their immature immune systems, making them susceptible to infectious diseases. The yolk plays an important role in early immune defence by showing relevant antioxidant and passive immunity capabilities during broiler embryonic development. The immunomodulatory effects of phytogenic compound carvacrol have been widely reported. After in ovo delivery in the amniotic fluid during embryonic development carvacrol is known to migrate to the yolk sac. However, it is unknown whether carvacrol in the yolk could enhance defence responsiveness in the yolk sac. Therefore, the aim of this study was to improve early immune function in chicken embryos, and it was hypothesized that in ovo delivery of carvacrol would result in immunomodulatory effects in the yolk sac, potentially improving post-hatch resilience.

METHODS

On embryonic day (E)17.5, either a saline (control) or carvacrol solution was injected into the amniotic fluid. Yolk sac tissue samples were collected at E19.5, and transcriptomic analyses using RNA sequencing were performed, following functional enrichment analyses comparing the control (saline) and carvacrol-injected groups.

RESULTS

The results showed that 268 genes were upregulated and 174 downregulated in the carvacrol group compared to the control (P < 0.05; logFC < -0.5 or log FC > 0.5). Functional analyses of these differentially expressed genes, using KEGG, REACTOME, and Gene Ontology databases, showed enrichment of several immune-related pathways. This included the pathways 'Antimicrobial peptides' (P = 0.001) and 'Chemoattractant activity' (P = 0.004), amongst others. Moreover, the 'NOD-like receptor signaling' pathway was enriched (P = 0.002). Antimicrobial peptides are part of the innate immune defence and are amongst the molecules produced after the nucleotide oligomerization domain (NOD)-like receptor pathway activation. While these responses may be associated with an inflammatory reaction to an exogenous threat, they could also indicate that in ovo delivery of carvacrol could prepare the newly hatched chick against bacterial pathogens by potentially promoting antimicrobial peptide production through activation of NOD-like receptor signaling in the yolk sac.

CONCLUSION

In conclusion, these findings suggest that in ovo delivery of carvacrol has the potential to enhance anti-pathogenic and pro-inflammatory responses in the yolk sac via upregulation of antimicrobial peptides, and NOD-like receptor pathways.

Ontogeny and function of the intestinal epithelial and innate immune cells during early development of chicks: to explore in ovo immunomodulatory nutrition

Intestinal epithelial cells (IECs) and innate immune cells in the gastrointestinal tract (GIT) of chickens play crucial roles in pathogens defense and maintaining gut health. However, their effectiveness influenced with their developmental and functional stages during pre and post hatch periods of chick. During embryonic development, differentiation and migration of these innate immune systems are tightly regulated by diverse cellular and molecular factors. The maturation and functionality of IECs are histologically evident starting embryonic day (ED) 14. Moreover, the innate immun cells, such as dendritic cells (DCs), macrophages, natural killer (NK) cells, and gamma-delta (γδ) T cells have showed developmental expression varation, while most identified by the 3rd days of incubation and capable of responsing to their cognate ligands of pathogens by ED 17, it may not efficient during posthatch period. In modern poultry production, in ovo feeding of bioactive substances is a topic of interest to maximize the protection capability of hatched chicks by enhancing improvement on the development of innate immune systems. However, their actions and effects on each distinct innate immune involved response are inconsistent and not clearly understood. Thus, summarizing the ontogeny and function of IECs, innate immunity systems, and interaction mechanisms of in ovo feeding of bioactive substances could provide baseline information for designing targeted in ovo feeding interventions to modulate cell waise specific innate immune systems.

Early-life immunomodulation by carvacrol delivered in ovo in broiler chickens

In the first 2 wk after hatching, broiler chickens are vulnerable to enteric pathogens due to underdeveloped gastrointestinal and immune systems. Carvacrol has been reported to improve digestive and immune functions. This study aimed to optimize immune development of broiler chickens by delivering carvacrol in ovo. Effects of 2 in ovo treatments delivered at embryonic day (E)17.5 (saline or carvacrol) were evaluated at 3 stages (E19.5, hatch, and d 14 posthatch). Hatchability, performance parameters, lymphoid organ and yolk sac weights were determined. Histomorphology assessment was performed for jejunal samples at hatch and bursa of Fabricius samples at hatch and d 14. Gene expression of immune-relevant genes was determined for jejunal, bursal, and yolk sac samples over time. At hatch, BW was 0.85% lower (P = 0.02) after in ovo carvacrol delivery compared to the controls. Interactions between in ovo treatment and age were found for gene expression. At hatch, carvacrol treatment resulted in lower expression of proinflammatory cytokines IL-8 and IFN-γ in the yolk sac compared to the controls (P = 0.05 and < .001, respectively) suggesting a potential role for carvacrol-mediated immune modulation. At d 14, carvacrol treatment led to lower expression of proinflammatory cytokine IL-6 in the bursa compared to the controls (P = 0.002). In ovo carvacrol delivery led to bursal histomorphometric changes, including a larger cortex in the bursal follicles (P = 0.03), and a higher cortex/medulla ratio (P = 0.04) compared to the controls, indicating increased B-cell stimulation and maturation. Main effects were found for carvacrol treatment in the jejunum, with overall higher expression of proinflammatory mediators IL-1β and NF-κB, and anti-inflammatory IL-10 compared to the controls (P = 0.04, 0.02, and 0.02 respectively) from E19.5 to d 14. Age-related main effects showed various alterations in expression dynamics of immune-related genes across all tissues over time. Our findings suggest changes in immune parameters occur as the chicken develops, but these mostly do not interact with in ovo carvacrol treatment. In ovo carvacrol treatment alters immune activity of broiler chickens independent of age.

Approaches to Enhance the Potency of Vaccines in Chickens

Outbreaks of avian pathogens such as Newcastle disease virus, avian influenza virus, and salmonella have a major impact on economies and food security worldwide. Some pathogens also pose a significant zoonotic potential, especially avian influenza viruses. Vaccination plays a key role in controlling many poultry diseases, and there are many vaccines licenced in the United Kingdom for diseases of poultry caused by viruses, bacteria, and parasites. However, these vaccines often do not provide complete protection and can cause unwanted side effects. Several factors affect the potency of poultry vaccines, including the type of vaccination used, the mechanism of delivery, and the use of adjuvants. Advancements in technology have led to the study and development of novel vaccines and vaccine adjuvants for use in poultry. These induce stronger immune responses compared with current vaccine technology and have the potential to protect against multiple poultry diseases. This review aims to discuss the existing poultry vaccine technology; the effect of delivery mechanisms on vaccine efficacy; the use of current and novel adjuvants; the ability to target antigens to antigen-presenting cells; and the use of probiotics, multivalent vaccines, and nanotechnology to enhance the potency of poultry vaccines.

Maternal riboflavin deficiency causes embryonic defects by activating ER stress-induced hepatocyte apoptosis pathway

Riboflavin deficiency (RD) induces liver damage, abnormal embryonic development, and high mortality. We hypothesized that the phenotype could be rescued by inhibiting ER stress. The objectives of the present study were to investigate the underlying molecular mechanisms of RD-induced embryonic defects using in vitro and in vivo models. Primary duck embryonic hepatocytes were treated with an ER stress inhibitor (4-PBA) or transfected with CHOP siRNA, and cultured in RD medium and riboflavin-sufficient (CON) medium for 8 days. Laying ducks (n = 20 cages/diet, 1 bird/cage) were fed an RD diet or CON diet for 14 wk, and the eggs were collected for hatching. At day 7 of incubation, the fertilized RD eggs were injected with or without 4-PBA into the yolk. RD decreased cell number and cell viability compared to the CON group, induced oxidative stress and apoptosis in primary duck embryonic hepatocytes. However, after being treated with an ER stress inhibitor (4-PBA) or transfected with CHOP siRNA, the apoptosis rate in RD hepatocytes decreased by 60.6 % and 86.1 %, respectively, being equal to the CON. These results indicated that RD-induced hepatocyte apoptosis is mediated by ER stress and the CHOP pathway. In vivo, RD embryos showed low hatchability, abnormal development, liver damage, ER stress, and apoptosis compared to the CON group. However, 4-PBA administration, as a model of ER stress inhibition, substantially restored embryonic development and alleviated liver damage in the RD group, including ER stress and apoptosis. Notably, hatchability in the RD group increased from 21.7 % to 72.7 % after 4-PBA treatment, though it remained less than the CON group (87.7 %). These results implicated ER stress-CHOP-apoptosis pathway as molecular mechanisms underlying RD-induced abnormal embryonic development and death, this target with potential for therapy or intervention.

Liver cancer in ovo models for preclinical testing

Immunotherapies have significantly improved the prognosis of patients with advanced hepatocellular carcinoma (HCC), although more than 70% of patients still do not respond to this first-line treatment. Many new combination strategies are currently being explored, which drastically increases the need for preclinical models that would allow large-scale testing of new immunotherapies and their combinations. We developed several in ovo (in the egg) human liver cancer models, based on human tumor xenografts of different liver cancer cell lines on the chicken embryo's chorioallantoic membrane. We characterized the angiogenesis, as well as the collagen accumulation and tumor immune microenvironment, and tested atezolizumab (anti-PD-L1) plus bevacizumab (anti-VEGF) treatment. Our results show the involvement of chicken immune cells in tumor growth, reproducing a classical non-inflamed "cold" as well as inflamed "hot" tumor status, depending on the in ovo liver cancer model. The treatment by atezolizumab and bevacizumab was highly efficient in the "hot" tumor model PLC/PRF/5 in ovo with the reduction of tumor size by 76% (p ≤ .0001) compared with the control, whereas the efficacy was limited in the "cold" Hep3B in ovo tumor. The contribution of the anti-PD-L1 blockade to the anti-tumoral effect in the PLC/PRF/5 in ovo model was demonstrated by the efficacy of atezolizumab monotherapy (p = .0080, compared with the control). To conclude, our study provides a detailed characterization and rational arguments that could help to partially replace conventional laboratory animals with a more ethical model, suited to the current needs of preclinical research of new immunotherapies for liver cancer.

Assessment of efficacy of chrysin in diabetes-associated cardiac complications in chick embryo and murine model

OBJECTIVES

Patients with type 2 diabetes or prolonged diabetic condition are webbed into cardiac complications. This study aimed to ascertain the utility of chick embryo as an alternative to the mammalian model for type 2 diabetes-induced cardiac complications and chrysin as a protective agent.

METHODS

Diabetes was activated in ovo model (chick embryo) using glucose along with β-hydroxybutyric acid. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide, Alamar, and Kenacid blue assay were used to compare with chrysin-administered group. Blood glucose level, total cholesterol, triglyceride, and high-density lipoprotein were considered as endpoints. Diabetes was induced in Wistar albino rats by administering a high-fat diet and a subdued dose of streptozotocin (35 mg/kg, b.w). Percentage of glycated hemoglobin, creatinine kinase-MB, tumor necrosis factor-α, and C-reactive protein were evaluated and compared with chrysin administered group.

KEY FINDINGS

Chrysin treatment improved elevated blood glucose levels and dyslipidemia in a diabetic group of whole embryos. Condensed cellular growth and protein content as well as enhanced cytotoxicity in ovo were shielded by chrysin. Chrysin reduced cardiac and inflammatory markers in diabetic rats and provided cellular protection to damage the heart of diabetic rats.

CONCLUSION

The protective action of chrysin in ovo model induced a secondary complication associated with diabetes, evidenced that the ovo model is an effective alternative in curtailing higher animal use in scientific research.

Alarming and calming: Dual functions of S100A9 on Mycoplasma gallisepticun infection in avian cells

Mycoplasma gallisepticum (MG) is the primary causative agent of chronic respiratory disease (CRD) in chickens, characterized by respiratory inflammation. S100A9 plays a pivotal role in modulating the inflammatory response to microbial pathogens. Our prior investigation revealed a significant upregulation of S100A9 in the lungs of chickens following MG infection. This study delves into the immunomodulatory effects of S100A9 during MG infection, demonstrating a notable increase in S100A9 levels in the lungs, immune organs, alveolar epithelial type II cells (AECII), and macrophage HD11 cells of MG-infected chicks and embryos. In MG-infected AECII cells, S100A9 overexpression significantly enhanced MG proliferation and adhesion, suppressed AVBD1, NFκB, pro-inflammatory factors (IL1β and TNFα), and chemokines, reduced apoptosis, and promoted cell proliferation, thereby facilitating MG infection. Conversely, inhibiting S100A9 produced opposing effects. In MG-infected HD11 cells, S100A9 impeded MG proliferation and adhesion, increased AVBD1, NFκB, pro-inflammatory factors, and chemokines, and induced cell apoptosis while inhibiting proliferation. Additional results demonstrated that S100A9 facilitates MG infection by modulating the TLR7/NFκB/JAK/STAT pathway in AECII/HD11 cells. In summary, S100A9 exhibits a dual role in activating/inhibiting the natural immune response through TLR7/NFκB/JAK/STAT pathway regulation. This dual role promotes MG infection in AECII cells while enabling MG to evade immune surveillance by HD11 cells, ultimately enhancing the overall infection process. These findings advance our understanding of host-pathogen interactions during MG infection and underscore S100A9's potential as a therapeutic target for CRD in chickens.

Chicken Secondary Lymphoid Tissues-Structure and Relevance in Immunological Research

Recent discoveries have indicated the importance of developing modern strategies for vaccinations, more ethical research models, and effective alternatives to antibiotic treatment in farm animals. Chickens (Gallus gallus) play a crucial role in this context given the commercial and economic relevance of poultry production worldwide and the search for analogies between the immune systems of humans and birds. Specifically, chicken secondary lymphoid tissues share similar features to their human counterparts. Chickens have several secondary or peripheral lymphoid tissues that are the sites where the adaptive immune response is initiated. The more general classification of these organs divides them into the spleen and skin-, pineal-, or mucosa-associated lymphoid tissues. Each of these tissues is further subdivided into separate lymphoid structures that perform specific and different functions along the animal's body. A review summarizing the state of the art of research on chicken secondary lymphoid organs is of great relevance for the design of future studies.

Bibliometric study of the application of the chicken embryo chorioallantoic membrane model in cancer research: the top 100 most cited articles

The chicken embryo chorioallantoic membrane (CAM) model has played a crucial role in various aspects of cancer research. The purpose of this study is to help researchers clarify the research direction and prospects of the CAM model. A bibliometric analysis was conducted on the top 100 most cited articles on use of the CAM model in tumour research, retrieved from the Web of Science Core Collection database. Tools such as Bibliometrix, VOSviewer, CiteSpace and Excel were utilized for the visualization network analysis. The 100 articles analysed were mainly from the USA, China and European countries such as Germany and France. Tumour research involving CAM model experiments demonstrated reliability and scientific rigor (average citation count = 156.2). The analysis of keywords, topics and subject areas revealed that the applications of this model ranged from the biological characteristics of tumours to molecular mechanisms and signaling pathways, to recent developments in nanotechnology and clinical applications. Additionally, nude mouse experiments have been more frequently performed in recent years. We conclude that the CAM model is efficient, simple and cost-effective, and has irreplaceable value in various aspects of cancer research. In the future, the CAM model can further contribute to nanotechnology research.

A new standardization for the use of chicken embryo: selection of target from the phage display library and infection

The filamentous bacteriophage M13KO7 (M13) is the most used in phage display (PD) technology and, like other phages, has been applied in several areas of medicine, agriculture, and in the food industry. One of the advantages is that they can modulate the immune response in the presence of pathogenic microorganisms, such as bacteria and viruses. This study evaluated the use of phage M13 in the chicken embryos model. We inoculated 13-day-old chicken embryos with Salmonella Pullorum (SP) and then evaluated survival for the presence of phage M13 or E. coli ER2738 (ECR) infected with M13. We found that the ECR bacterium inhibits SP multiplication in 0.32 (M13-infected ECR) or 0.44 log UFC/mL (M13-uninfected ECR) and that the ECR-free phage M13 from the PD library can be used in chicken embryo models. This work provides the use of the chicken embryo as a model to study systemic infection and can be employed as an analysis tool for various peptides that M13 can express from PD selection. KEY POINTS: • SP-infected chicken embryo can be a helpful model of systemic infection for different tests. • Phage M13 does not lead to embryonic mortality or cause serious injury to embryos. • Phage M13 from the PD library can be used in chicken embryo model tests.

Critical Involvement of the Thioredoxin Reductase Gene (trxB) in Salmonella Gallinarum-Induced Systemic Infection in Chickens

Salmonella enterica serovar Gallinarum biovar Gallinarum (SG) causes fowl typhoid, a notifiable infectious disease in poultry. However, the pathogenic mechanism of SG-induced systemic infection in chickens remains unclear. Thioredoxin reductase (TrxB) is a redox protein crucial for regulating various enzyme activities in Salmonella serovar, but the role in SG-induced chicken systemic infection has yet to be determined. Here, we constructed a mutant SG strain lacking the trxB gene (trxB::Cm) and used chicken embryo inoculation and chicken oral infection to investigate the role of trxB gene in the pathogenicity of SG. Our results showed that trxB::Cm exhibited no apparent differences in colony morphology and growth conditions but exhibited reduced tolerance to H2O2 and increased resistance to bile acids. In the chicken embryo inoculation model, there was no significant difference in the pathogenicity of trxB::Cm and wild-type (WT) strains. In the chicken oral infection, the WT-infected group exhibited typical clinical symptoms of fowl typhoid, with complete mortality between days 6 and 9 post infection. In contrast, the trxB::Cm group showed a 100% survival rate, with no apparent clinical symptoms or pathological changes observed. The viable bacterial counts in the liver and spleen of the trxB::Cm-infected group were significantly reduced, accompanied by decreased expression of cytokines and chemokines (IL-1β, IL-6, IL-12, CXCLi1, TNF-α, and IFN-γ), which were significantly lower than those in the WT group. These results show that the pathogenicity of the trxB-deficient strain was significantly attenuated, indicating that the trxB gene is a crucial virulence factor in SG-induced systemic infection in chickens, suggesting that trxB may become a potentially effective target for controlling and preventing SG infection in chickens.

The Functional Mechanism of BP9 in Promoting B Cell Differentiation and Inducing Antigen Presentation

The Bursa of Fabricius, an avian unique humoral immune organ, is instrumental to B cell development. Bursal-derived peptide BP9 fosters B-cell development and formation. Yet, the exact mechanism wherein BP9 impacts B cell differentiation and antigenic presentation remains undefined. In this paper, B cell activation and differentiation in the spleen cells from mice immunized with the AIV vaccine and BP9 were detected following flow cytometry (FCM) analysis. Furthermore, the molecular mechanism of BP9 in B cell differentiation in vivo was investigated with RNA sequencing technology. To verify the potential functional mechanism of BP9 in the antigenic presentation process, the transcriptome molecular basis of chicken macrophages stimulated by BP9 was measured via high-throughput sequencing technology. The results proved that when given in experimental dosages, BP9 notably accelerated total B cells, and enhanced B-cell differentiation and plasma cell production. The gene expression profiles of B cells from mice immunized with 0.01 mg/mL BP9 and AIV vaccine disclosed that 0.01 mg/mL BP9 initiated the enrichment of several biological functions and significantly stimulated key B-cell pathways in immunized mice. Crucially, a total of 4093 differentially expressed genes were identified in B cells with BP9 stimulation, including 943 upregulated genes and 3150 downregulated genes. Additionally, BP9 induced various cytokine productions in the chicken macrophage HD11 cells and activated 9 upregulated and 20 downregulated differential miRNAs, which were involved in various signal and biological processes. Furthermore, BP9 stimulated the activation of multiple transcription factors in HD11 cells, which was related to antigen presentation processes. In summary, these results suggested that BP9 might promote B cell differentiation and induce antigen presentation, which might provide the valuable insights into the mechanism of B cell differentiation upon bursal-derived immunomodulating peptide stimulation and provide a solid experimental groundwork for enhancing vaccine-induced immunity.

In vitro and in ovo photodynamic efficacy of nebulized curcumin-loaded tetraether lipid liposomes prepared by DC as stable drug delivery system

Lung cancer is one of the most common causes of high mortality worldwide. Current treatment strategies, e.g., surgery, radiotherapy, chemotherapy, and immunotherapy, insufficiently affect the overall outcome. In this study, we used curcumin as a natural photosensitizer in photodynamic therapy and encapsulated it in liposomes consisting of stabilizing tetraether lipids aiming for a pulmonary drug delivery system against lung cancer. The liposomes with either hydrolyzed glycerol-dialkyl-glycerol tetraether (hGDGT) in different ratios or hydrolyzed glycerol-dialkyl-nonitol tetraether (hGDNT) were prepared by dual centrifugation (DC), an innovative method for liposome preparation. The liposomes' physicochemical characteristics before and after nebulization and other nebulization characteristics confirmed their suitability. Morphological characterization using atomic force and transmission electron microscopy showed proper vesicular structures indicative of liposomes. Qualitative and quantitative uptake of the curcumin-loaded liposomes in lung adenocarcinoma (A549) cells was visualized and proven. Phototoxic effects of the liposomes were detected on A549 cells, showing decreased cell viability. The generation of reactive oxygen species required for PDT and disruption of mitochondrial membrane potential were confirmed. Moreover, the chorioallantoic membrane (CAM) model was used to further evaluate biocompatibility and photodynamic efficacy in a 3D cell culture context. Photodynamic efficacy was assessed by PET/CT after nebulization of the liposomes onto the xenografted tumors on the CAM with subsequent irradiation. The physicochemical properties and the efficacy of tetraether lipid liposomes encapsulating curcumin, especially liposomes containing hGDNT, in 2D and 3D cell cultures seem promising for future PDT usage against lung cancer.

Evaluating the photodynamic efficacy of nebulized curcumin-loaded liposomes prepared by thin-film hydration and dual centrifugation: In vitro and in ovo studies

Lung cancer, one of the most common causes of high mortality worldwide, still lacks appropriate and convenient treatment options. Photodynamic therapy (PDT) has shown promising results against cancer, especially in recent years. However, pulmonary drug delivery of the predominantly hydrophobic photosensitizers still represents a significant obstacle. Nebulizing DPPC/Cholesterol liposomes loaded with the photosensitizer curcumin via a vibrating mesh nebulizer might overcome current restrictions. In this study, the liposomes were prepared by conventional thin-film hydration and two other methods based on dual centrifugation. The liposomes' physicochemical properties were determined before and after nebulization, showing that liposomes do not undergo any changes. However, morphological characterization of the differently prepared liposomes revealed structural differences between the methods in terms of lamellarity. Internalization of curcumin in lung adenocarcinoma (A549) cells was visualized and quantified. The generation of reactive oxygen species because of the photoreaction was also proven. The photodynamic efficacy of the liposomal formulations was tested against A549 cells. They revealed different phototoxic responses at different radiant exposures. Furthermore, the photodynamic efficacy was investigated after nebulizing curcumin-loaded liposomes onto xenografted tumors on the CAM, followed by irradiation, and evaluated using positron emission tomography/computed tomography and histological analysis. A decrease in tumor metabolism could be observed. Based on the efficacy of curcumin-loaded liposomes in 2D and 3D models, liposomes, especially with prior film formation, can be considered a promising approach for PDT against lung cancer.

In vivo label-free tissue histology through a microstructured imaging window

Tissue histopathology, based on hematoxylin and eosin (H&E) staining of thin tissue slices, is the gold standard for the evaluation of the immune reaction to the implant of a biomaterial. It is based on lengthy and costly procedures that do not allow longitudinal studies. The use of non-linear excitation microscopy in vivo, largely label-free, has the potential to overcome these limitations. With this purpose, we develop and validate an implantable microstructured device for the non-linear excitation microscopy assessment of the immune reaction to an implanted biomaterial label-free. The microstructured device, shaped as a matrix of regular 3D lattices, is obtained by two-photon laser polymerization. It is subsequently implanted in the chorioallantoic membrane (CAM) of embryonated chicken eggs for 7 days to act as an intrinsic 3D reference frame for cell counting and identification. The histological analysis based on H&E images of the tissue sections sampled around the implanted microstructures is compared to non-linear excitation and confocal images to build a cell atlas that correlates the histological observations to the label-free images. In this way, we can quantify the number of cells recruited in the tissue reconstituted in the microstructures and identify granulocytes on label-free images within and outside the microstructures. Collagen and microvessels are also identified by means of second-harmonic generation and autofluorescence imaging. The analysis indicates that the tissue reaction to implanted microstructures is like the one typical of CAM healing after injury, without a massive foreign body reaction. This opens the path to the use of similar microstructures coupled to a biomaterial, to image in vivo the regenerating interface between a tissue and a biomaterial with label-free non-linear excitation microscopy. This promises to be a transformative approach, alternative to conventional histopathology, for the bioengineering and the validation of biomaterials in in vivo longitudinal studies.

Impact of Human Adenovirus 36 on Embryonated Chicken Eggs: Insights into Growth Mechanisms

Human adenovirus 36 (HAdV-D36) is presently the sole virus identified to be associated with an elevated risk of obesity in both humans and animals. However, its impact on embryonated chicken eggs (ECEs) remains unexplored. This study endeavoured to examine the influence of HAdV-D36 on embryonic development by utilizing embryonated chicken eggs as a dynamic model. To simulate various infection routes, the allantoic cavity and the yolk sac of ECEs were inoculated with HAdV-D36. Subsequently, embryos from both the experimental (inoculated with virus) and control (inoculated with PBS) groups were weighed and subjected to daily histological examination. The daily embryo weights were assessed and compared between groups using the Shapiro-Wilk test. Histopathological changes in tissues were examined and compared between the tested and control groups to ascertain physiological alterations induced by the virus. Our study confirmed a significant increase in the body weight of ECEs. However, this phenomenon was not attributable to adipose tissue development; rather, it was characterized by an augmented number of cells in all observed tissues compared to control subjects. We posit that HAdV-D36 may impact developing organisms through mechanisms other than enhanced adipose tissue development. Specifically, our findings indicate an increased number of cells in all tissues, a phenomenon that occurs through an as-yet-unexplored pathway.

Exploring the predictive power of jejunal microbiome composition in clinical and subclinical necrotic enteritis caused by Clostridium perfringens: insights from a broiler chicken model

BACKGROUND

Necrotic enteritis (NE) is a severe intestinal infection that affects both humans and poultry. It is caused by the bacterium Clostridium perfringens (CP), but the precise mechanisms underlying the disease pathogenesis remain elusive. This study aims to develop an NE broiler chicken model, explore the impact of the microbiome on NE pathogenesis, and study the virulence of CP isolates with different toxin gene combinations.

METHODS

This study established an animal disease model for NE in broiler chickens. The methodology encompassed inducing abrupt protein changes and immunosuppression in the first experiment, and in the second, challenging chickens with CP isolates containing various toxin genes. NE was evaluated through gross and histopathological scoring of the jejunum. Subsequently, jejunal contents were collected from these birds for microbiome analysis via 16S rRNA amplicon sequencing, followed by sequence analysis to investigate microbial diversity and abundance, employing different bioinformatic approaches.

RESULTS

Our findings reveal that CP infection, combined with an abrupt increase in dietary protein concentration and/or infection with the immunosuppressive variant infectious bursal disease virus (vIBDV), predisposed birds to NE development. We observed a significant decrease (p < 0.0001) in the abundance of Lactobacillus and Romboutsia genera in the jejunum, accompanied by a notable increase (p < 0.0001) in Clostridium and Escherichia. Jejunal microbial dysbiosis and severe NE lesions were particularly evident in birds infected with CP isolates containing cpa, netB, tpeL, and cpb2 toxin genes, compared to CP isolates with other toxin gene combinations. Notably, birds that did not develop clinical or subclinical NE following CP infection exhibited a significantly higher (p < 0.0001) level of Romboutsia. These findings shed light on the complex interplay between CP infection, the gut microbiome, and NE pathogenesis in broiler chickens.

CONCLUSION

Our study establishes that dysbiosis within the jejunal microbiome serves as a reliable biomarker for detecting subclinical and clinical NE in broiler chicken models. Additionally, we identify the potential of the genera Romboutsia and Lactobacillus as promising candidates for probiotic development, offering effective alternatives to antibiotics in NE prevention and control.

Assessment of the Teratogenic Effect of Drugs on the Chicken Embryo

Pre-clinical trials are an essential step that underpins the drug discovery, development, and safety process. During this process, animal testing is performed to determine the safety of new compounds and any potential adverse effects. Developmental toxicity tests are carried out to verify whether the drug has potential to cause congenital anomalies to the developing embryo/fetus. Chicken embryos are very useful for these purposes and present several advantages, such as low cost of production and housing, easy handling and manipulation, and rapid development in addition to sharing similarities to the human embryo at molecular, cellular, and anatomical levels. In this chapter, we bring methods for using the chicken embryo model for testing the teratogenic effects of drugs and assessing the main outcomes of them.

How to Break through the Bottlenecks of in Ovo Vaccination in Poultry Farming

Poultry farming is one of the pillar industries of global animal husbandry. In order to guarantee production, poultry are frequently vaccinated from the moment they are hatched. Even so, the initial immunity of chicks is still very poor as they are in the "window period" of immune protection. In ovo vaccination pushes the initial immunization time forward to the incubation period, thereby providing earlier immune protection for chicks. In ovo vaccination is currently a research hotspot of poultry disease prevention and control, which is in line with the intensification of poultry production. However, the vaccines currently available for in ovo vaccination are limited and cannot meet the needs of industrial development, so how to efficiently activate the adaptive immune response of chicken embryos becomes the key to restrict product development and technological progress of in ovo vaccination. Its breakthrough, to a large extent, depends on systematic illustration of the mechanism underlying the adaptive immune response post immunization. Clarification of this issue will provide us with theoretical support and potential solutions for the development of novel vaccines for in ovo vaccination, the augmentation of efficacy of current vaccines and the optimization of immune programs.

Modern Photodynamic Glioblastoma Therapy Using Curcumin- or Parietin-Loaded Lipid Nanoparticles in a CAM Model Study

Natural photosensitizers, such as curcumin or parietin, play a vital role in photodynamic therapy (PDT), causing a light-mediated reaction that kills cancer cells. PDT is a promising treatment option for glioblastoma, especially when combined with nanoscale drug delivery systems. The curcumin- or parietin-loaded lipid nanoparticles were prepared via dual asymmetric centrifugation and subsequently characterized through physicochemical analyses including dynamic light scattering, laser Doppler velocimetry, and atomic force microscopy. The combination of PDT and lipid nanoparticles has been evaluated in vitro regarding uptake, safety, and efficacy. The extensive and well-vascularized chorioallantois membrane (CAM) of fertilized hen's eggs offers an optimal platform for three-dimensional cell culture, which has been used in this study to evaluate the photodynamic efficacy of lipid nanoparticles against glioblastoma cells. In contrast to other animal models, the CAM model lacks a mature immune system in an early stage, facilitating the growth of xenografts without rejection. Treatment of xenografted U87 glioblastoma cells on CAM was performed to assess the effects on tumor viability, growth, and angiogenesis. The xenografts and the surrounding blood vessels were targeted through topical application, and the effects of photodynamic therapy have been confirmed microscopically and via positron emission tomography and X-ray computed tomography. Finally, the excised xenografts embedded in the CAM were analyzed histologically by hematoxylin and eosin and KI67 staining.

Human Non-Small Cell Lung Cancer-Chicken Embryo Chorioallantoic Membrane Tumor Models for Experimental Cancer Treatments

To promote the preclinical development of new treatments for non-small cell lung cancer (NSCLC), we established NSCLC xenograft tumor assays on the chorioallantoic membrane (CAM) of chicken embryos. Five NSCLC cell lines were compared for tumor take rate, tumor growth, and embryo survival. Two of these, A549 and H460 CAM tumors, were histologically characterized and tested for susceptibility to systemic chemotherapy and gene delivery using viral vectors. All cell lines were efficiently engrafted with minimal effect on embryo survival. The A549 cells formed slowly growing tumors, with a relatively uniform distribution of cancer cells and stroma cells, while the H460 cells formed large tumors containing mostly proliferating cancer cells in a bed of vascularized connective tissue. Tumor growth was inhibited via systemic treatment with Pemetrexed and Cisplatin, a chemotherapy combination that is often used to treat patients with advanced NSCLC. Lentiviral and adenoviral vectors expressing firefly luciferase transduced NSCLC tumors in vivo. The adenovirus vector yielded more than 100-fold higher luminescence intensities after a single administration than could be achieved with multiple lentiviral vector deliveries. The adenovirus vector also transduced CAM tissue and organs of developing embryos. Adenovirus delivery to tumors was 100-10,000-fold more efficient than to embryo organs. In conclusion, established human NSCLC-CAM tumor models provide convenient in vivo assays to rapidly evaluate new cancer therapies, particularly cancer gene therapies.

Alendronate induces skeletal alterations in the chicken embryonic development model

Alendronate, a nitrogen-containing bisphosphonate, has reported long-term clinical success in the management of distinct bone-related conditions, particularly in the modulation of post-menopausal osteoporosis. Nonetheless, whether the inhibitory activity over osteoclastic cells' functionality is widely acknowledged, contradictory evidence arises from the assessment of alendronate activity over osteoblastic populations. This may be of particular relevance in situations in which bone formation exceeds bone resorption, with further emphasis on embryonic development, since alendronate can cross the placental barrier and alendronate-based therapies are being extended into women of reproductive age. Accordingly, the present study aims to assess the effects of alendronate, at distinct concentrations (1.5E-10M to 1.5E-7M) on bone tissue development, within a translational animal model - the embryonic chicken development model. Embryos, at the beginning of osteogenesis (day 7) were exposed to different alendronate concentrations for 4 days. Embryos were following characterized for skeletal development by histomorphometric analysis upon histochemical staining, microtomographic analysis, and gene expression assessment of genes related to osteoclastogenic/osteoclastic and osteoblastogenic/osteogenic differentiation, as well as to the immuno-inflammatory activation. The findings revealed that exposure to alendronate had a dose-dependent impact on skeletal growth and mineralization. This effect was evidenced by diminished bone volume and reduced bone surface parameters, with the 1.5E-7M concentration leading to a remarkable reduction of over 50%. Additionally, a decreased osteoclastogenic/osteoclastic gene expression was verified, associated with a diminished osteoblastogenic/osteogenic program - within the 30-50% range for 1.5E-7 M, supporting the diminished bone formation process. An increased inflammatory activation may contribute, at least in part, to the attained outcomes. Overall present findings suggest a negative influence of alendronate on the embryonic bone development process in a dose-dependent manner, highlighting the potential risk of alendronate use during embryonic development.

Feasibility of the chick chorioallantoic membrane model for preclinical studies on tumor radiofrequency ablation

BACKGROUND

We evaluated the feasibility of a chick chorioallantoic membrane (CAM) tumor model for preclinical research on tumor radiofrequency ablation (RFA).

METHODS

Fertilized chicken eggs were incubated and divided into five cohorts: RFA for 30 s (n = 5), RFA for 60 s (n = 5), RFA for 120 s (n = 4), sham (n = 8), and controls (n = 6). Xenografting using pancreatic neuroendocrine tumor cells of the BON-1 cell line was performed on embryonic day (ED) 8. The RFA was performed on ED 12. Survival, stereomicroscopic observations, and histological observations using hematoxylin-eosin (H&E) and Ki67 staining were evaluated.

RESULTS

The survival rates in the 30-s, 60-s, and 120-s, sham and control cohort were 60%, 60%, 0%, 100%, and 50%, respectively. Signs of bleeding and heat damage were common findings in the evaluation of stereomicroscopic observations. Histological examination could be performed in all but one embryo. Heat damage, bleeding, thrombosis, and leukocyte infiltration and hyperemia were regular findings in H&E-stained cuts. A complete absence of Ki67 staining was recorded in 33.3% and 50% of embryos in the 30-s and 60-s cohorts that survived until ED 14, respectively.

CONCLUSIONS

The CAM model is a feasible and suiting research model for tumor RFA with many advantages over other animal models. It offers the opportunity to conduct in vivo research under standardized conditions. Further studies are needed to optimize this model for tumor ablations in order to explore promising but unrefined strategies like the combination of RFA and immunotherapy.

RELEVANCE STATEMENT

The chick chorioallantoic membrane model allows in vivo research on tumor radiofrequency ablation under standardized conditions that may enable enhanced understanding on combined therapies while ensuring animal welfare in concordance with the "Three Rs."

KEY POINTS

• The chorioallantoic membrane model is feasible and suiting for tumor radiofrequency ablation. • Radiofrequency ablation regularly achieved reduction but not eradication of Ki67 staining. • Histological evaluation showed findings comparable to changes in humans after RFA. • The chorioallantoic membrane model can enable studies on combined therapies after optimization.

Human Monocytes Are Suitable Carriers for the Delivery of Oncolytic Herpes Simplex Virus Type 1 In Vitro and in a Chicken Embryo Chorioallantoic Membrane Model of Cancer

Oncolytic viruses (OVs) are promising therapeutics for tumors with a poor prognosis. An OV based on herpes simplex virus type 1 (oHSV-1), talimogene laherparepvec (T-VEC), has been recently approved by the Food and Drug Administration (FDA) and by the European Medicines Agency (EMA) for the treatment of unresectable melanoma. T-VEC, like most OVs, is administered via intratumoral injection, underlining the unresolved problem of the systemic delivery of the oncolytic agent for the treatment of metastases and deep-seated tumors. To address this drawback, cells with a tropism for tumors can be loaded ex vivo with OVs and used as carriers for systemic oncolytic virotherapy. Here, we evaluated human monocytes as carrier cells for a prototype oHSV-1 with a similar genetic backbone as T-VEC. Many tumors specifically recruit monocytes from the bloodstream, and autologous monocytes can be obtained from peripheral blood. We demonstrate here that oHSV-1-loaded primary human monocytes migrated in vitro towards epithelial cancer cells of different origin. Moreover, human monocytic leukemia cells selectively delivered oHSV-1 to human head-and-neck xenograft tumors grown on the chorioallantoic membrane (CAM) of fertilized chicken eggs after intravascular injection. Thus, our work shows that monocytes are promising carriers for the delivery of oHSV-1s in vivo, deserving further investigation in animal models.

Comparative Transcriptome Analysis Reveals the Innate Immune Response to Mycoplasma gallisepticum Infection in Chicken Embryos and Newly Hatched Chicks

Mycoplasma gallisepticum (MG) is a major cause of chronic respiratory diseases in chickens, with both horizontal and vertical transmission modes and varying degrees of impact on different ages. The innate immune response is crucial in resisting MG infection. Therefore, this study aimed to investigate the innate immune response of chicken embryos and newly hatched chicks to MG infection using comparative RNA-seq analysis. We found that MG infection caused weight loss and immune damage in both chicken embryos and chicks. Transcriptome sequencing analysis revealed that infected chicken embryos had a stronger immune response than chicks, as evidenced by the higher number of differentially expressed genes associated with innate immunity and inflammation. Toll-like receptor and cytokine-mediated pathways were the primary immune response pathways in both embryos and chicks. Furthermore, TLR7 signaling may play an essential role in the innate immune response to MG infection. Overall, this study sheds light on the development of innate immunity to MG infection in chickens and can help in devising disease control strategies.

An in vivo avian model of human melanoma to perform rapid and robust preclinical studies

Metastatic melanoma patients carrying a BRAF^V600 mutation can be treated with a combination of BRAF and MEK inhibitors (BRAFi/MEKi), but innate and acquired resistance invariably occurs. Predicting patient response to targeted therapies is crucial to guide clinical decision. We describe here the development of a highly efficient patient-derived xenograft model adapted to patient melanoma biopsies, using the avian embryo as a host (AVI-PDX^TM ). In this in vivo paradigm, we depict a fast and reproducible tumor engraftment of patient samples within the embryonic skin, preserving key molecular and phenotypic features. We show that sensitivity and resistance to BRAFi/MEKi can be reliably modeled in these AVI-PDX^TM , as well as synergies with other drugs. We further provide proof-of-concept that the AVI-PDX^TM models the diversity of responses of melanoma patients to BRAFi/MEKi, within days, hence positioning it as a valuable tool for the design of personalized medicine assays and for the evaluation of novel combination strategies.

The chick embryo chorioallantoic membrane patient-derived xenograft (PDX) model

The chick embryo chorioallantoic membrane (CAM) CAM is an extraembryonic membrane generated by the fusion of the chorion with the vascularized allantoic membrane. It performs multiple functions during embryonic development, including respiration, calcium transport from the eggshell, acid-base homeostasis, and ion/water reabsorption from the allantoic fluid. The CAM is a widely used model for the study of angiogenesis, anti-angiogenesis, tumor growth, and metastasis as well as drug efficacy. Ethical approval is omitted if experiments are terminated at embryonic day 14 in most countries, facilitating screenings of pharmacological or physics-based therapies with high reproducibility at large scales supporting the 3Rs principle. Being naturally immunodeficient, the chick embryo accepts transplantation from various tissues and species without immune response. This review article is focused on the analysis of the literature and personal data concerning the effects of patient-derived xenografts (PDX) on the CAM.

Chorioallantoic Membrane Assay at the Cross-Roads of Adipose-Tissue-Derived Stem Cell Research

With a history of more than 100 years of different applications in various scientific fields, the chicken chorioallantoic membrane (CAM) assay has proven itself to be an exceptional scientific model that meets the requirements of the replacement, reduction, and refinement principle (3R principle). As one of three extraembryonic avian membranes, the CAM is responsible for fetal respiration, metabolism, and protection. The model provides a unique constellation of immunological, vascular, and extracellular properties while being affordable and reliable at the same time. It can be utilized for research purposes in cancer biology, angiogenesis, virology, and toxicology and has recently been used for biochemistry, pharmaceutical research, and stem cell biology. Stem cells and, in particular, mesenchymal stem cells derived from adipose tissue (ADSCs) are emerging subjects for novel therapeutic strategies in the fields of tissue regeneration and personalized medicine. Because of their easy accessibility, differentiation profile, immunomodulatory properties, and cytokine repertoire, ADSCs have already been established for different preclinical applications in the files mentioned above. In this review, we aim to highlight and identify some of the cross-sections for the potential utilization of the CAM model for ADSC studies with a focus on wound healing and tissue engineering, as well as oncological research, e.g., sarcomas. Hereby, the focus lies on the combination of existing evidence and experience of such intersections with a potential utilization of the CAM model for further research on ADSCs.

Genome analysis reveals hepatic transcriptional reprogramming changes mediated by enhancers during chick embryonic development

The liver undergoes a slow process for lipid deposition during chick embryonic period. However, the underlying physiological and molecular mechanisms are still unclear. Therefore, the aim of the current study was to reveal the epigenetic mechanism of hepatic transcriptional reprogramming changes based on the integration analysis of RNA-seq and H3K27ac labeled CUT&Tag. Results showed that lipid contents increased gradually with the embryonic age (E) 11, E15, and E19 based on morphological analysis of Hematoxylin-eosin and Oil Red O staining as well as total triglyceride and cholesterol detection. The hepatic protein level of SREBP-1c was higher in E19 when compared with that in E11 and E15, while H3K27ac and H3K4me2 levels declined from E11 to E19. Differential expression genes (DEGs) among these 3 embryonic ages were determined by transcriptome analysis. A total of 107 and 46 genes were gradually upregulated and downregulated respectively with the embryonic age. Meanwhile, differential H3K27ac occupancy in chromatin was investigated. But the integration analysis of RNA-seq and CUT&Tag data showed that the overlap genes were less between DEGs and target genes of differential peaks in the promoter regions. Further, some KEGG pathways enriched from target genes of typical enhancer were overlapped with those from DEGs in transcriptome analysis such as insulin, FoxO, MAPK signaling pathways which were related to lipid metabolism. DNA motif analysis identify 8 and 10 transcription factors (TFs) based on up and down differential peaks individually among E11, E15, and E19 stages where 7 TFs were overlapped including COUP-TFII, FOXM1, FOXA1, HNF4A, RXR, ERRA, FOXA2. These results indicated that H3K27ac histone modification is involved in the transcriptional reprogramming regulation during embryonic development, which could recruit TFs binding to mediate differential enhancer activation. Differential activated enhancer impels dynamic transcriptional reprogramming towards lipid metabolism to promote the occurrence of special phenotype of hepatic lipid deposition.

Exploring the Expression and Function of cTyro3, a Candidate Zika Virus Receptor, in the Embryonic Chicken Brain and Inner Ear

The transmembrane protein Axl was proposed as an entry receptor for Zika virus (ZIKV) infection in vitro, but conflicting results from in vivo studies have made it difficult to establish Axl as a physiologically relevant ZIKV receptor. Both the functional redundancy of receptors and the experimental model used can lead to variable results. Therefore, it can be informative to explore alternative animal models to analyze ZIKV receptor candidates as an aid in discovering antivirals. This study used chicken embryos to examine the role of chicken Tyro3 (cTyro3), the equivalent of human Axl. Results show that endogenous cTyro3 mRNA expression overlaps with previously described hot spots of ZIKV infectivity in the brain and inner ear. We asked if ectopic expression or knockdown of cTyro3 influenced ZIKV infection in embryos. Tol2 vectors or replication-competent avian retroviruses were used in ovo to introduce full-length or truncated (presumed dominant-negative) cTyro3, respectively, into the neural tube on embryonic day two (E2). ZIKV was delivered to the brain 24 h later. cTyro3 manipulations did not alter ZIKV infection or cell death in the E5/E6 brain. Moreover, delivery of truncated cTyro3 variants to the E3 otocyst had no effect on inner ear formation on E6 or E10.

The CAM Model-Q&A with Experts

The chick chorioallantoic membrane (CAM), as an extraembryonic tissue layer generated by the fusion of the chorion with the vascularized allantoic membrane, is easily accessible for manipulation. Indeed, grafting tumor cells on the CAM lets xenografts/ovografts develop in a few days for further investigations. Thus, the CAM model represents an alternative test system that is a simple, fast, and low-cost tool to study tumor growth, drug response, or angiogenesis in vivo. Recently, a new era for the CAM model in immune-oncology-based drug discovery has been opened up. Although there are many advantages offering extraordinary and unique applications in cancer research, it has also disadvantages and limitations. This review will discuss the pros and cons with experts in the field.

Bridging the In Vitro to In Vivo gap: Using the Chick Embryo Model to Accelerate Nanoparticle Validation and Qualification for In Vivo studies

We postulate that nanoparticles (NPs) for use in therapeutic applications have largely not realized their clinical potential due to an overall inability to use in vitro results to predict NP performance in vivo. The avian embryo and associated chorioallantoic membrane (CAM) has emerged as an in vivo preclinical model that bridges the gap between in vitro and in vivo, enabling rapid screening of NP behavior under physiologically relevant conditions and providing a rapid, accessible, economical, and more ethical means of qualifying nanoparticles for in vivo use. The CAM is highly vascularized and mimics the diverging/converging vasculature of the liver, spleen, and lungs that serve as nanoparticle traps. Intravital imaging of fluorescently labeled NPs injected into the CAM vasculature enables immediate assessment and quantification of nano-bio interactions at the individual NP scale in any tissue of interest that is perfused with a microvasculature. In this review, we highlight how utilization of the avian embryo and its CAM as a preclinical model can be used to understand NP stability in blood and tissues, extravasation, biocompatibility, and NP distribution over time, thereby serving to identify a subset of NPs with the requisite stability and performance to introduce into rodent models and enabling the development of structure-property relationships and NP optimization without the sacrifice of large populations of mice or other rodents. We then review how the chicken embryo and CAM model systems have been used to accelerate the development of NP delivery and imaging agents by allowing direct visualization of targeted (active) and nontargeted (passive) NP binding, internalization, and cargo delivery to individual cells (of relevance for the treatment of leukemia and metastatic cancer) and cellular ensembles (e.g., cancer xenografts of interest for treatment or imaging of cancer tumors). We conclude by showcasing emerging techniques for the utilization of the CAM in future nano-bio studies.

'Cannibalism' of exogenous DNA sequences: The ancestral form of adaptive immunity which entails recognition of danger

Adaptive immunity is a sophisticated form of immune response capable of retaining the molecular memory of a very great diversity of target antigens (epitopes) as non-self. It is capable of reactivating itself upon a second encounter with an immunoglobulin or T-cell receptor antigen-binding site with a known epitope that had previously primed the host immune system. It has long been considered that adaptive immunity is a highly evolved form of non-self recognition that appeared quite late in speciation and complemented a more generalist response called innate immunity. Innate immunity offers a relatively non-specific defense (although mediated by sensors that could specifically recognize virus or bacteria compounds) and which does not retain a memory of the danger. But this notion of recent acquisition of adaptive immunity is challenged by the fact that another form of specific recognition mechanisms already existed in prokaryotes that may be able to specifically auto-protect against external danger. This recognition mechanism can be considered a primitive form of specific (adaptive) non-self recognition. It is based on the fact that many archaea and bacteria use a genome editing system that confers the ability to appropriate viral DNA sequences allowing prokaryotes to prevent host damage through a mechanism very similar to adaptive immunity. This is indistinctly called, 'endogenization of foreign DNA' or 'viral DNA predation' or, more pictorially 'DNA cannibalism'. For several years evidence has been accumulating, highlighting the crucial role of endogenization of foreign DNA in the fundamental processes related to adaptive immunity and leading to a change in the dogma that adaptive immunity appeared late in speciation.

The Chick Embryo Xenograft Model for Malignant Pleural Mesothelioma: A Cost and Time Efficient 3Rs Model for Drug Target Evaluation

Malignant pleural mesothelioma (MPM) has limited treatment options and poor prognosis. Frequent inactivation of the tumour suppressors BAP1, NF2 and P16 may differentially sensitise tumours to treatments. We have established chick chorioallantoic membrane (CAM) xenograft models of low-passage MPM cell lines and protocols for evaluating drug responses. Ten cell lines, representing the spectrum of histological subtypes and tumour suppressor status, were dual labelled for fluorescence/bioluminescence imaging and implanted on the CAM at E7. Bioluminescence was used to assess viability of primary tumours, which were excised at E14 for immunohistological staining or real-time PCR. All MPM cell lines engrafted efficiently forming vascularised nodules, however their size, morphology and interaction with chick cells varied. MPM phenotypes including local invasion, fibroblast recruitment, tumour angiogenesis and vascular remodelling were evident. Bioluminescence imaging could be used to reliably estimate tumour burden pre- and post-treatment, correlating with tumour weight and Ki-67 staining. In conclusion, MPM-CAM models recapitulate important features of the disease and are suitable to assess drug targets using a broad range of MPM cell lines that allow histological or genetic stratification. They are amenable to multi-modal imaging, potentially offering a time and cost-efficient, 3Rs-compliant alternative to rodent xenograft models to prioritise candidate compounds from in vitro studies.

Integrated Transcriptome Analysis Reveals mRNA-miRNA Pathway Crosstalk in Roman Laying Hens' Immune Organs Induced by AFB1

Aflatoxin B1 (AFB1) is a widely distributed contaminant in moldy corn, rice, soybean, and oil crops. Many studies have revealed its adverse effects, such as carcinogenicity, immunotoxicity, and hepatotoxicity, on the health of humans and animals. To investigate the immunotoxic effects on chicken immune organs induced by AFB1, we integrated RNA and small-RNA sequencing data of the spleen and the bursa of Fabricius to elucidate the response of the differentially expressed transcriptional profiles and related pathways. AFB1 consumption negatively influenced egg quality, but no obvious organ damage was observed compared to that of the control group. We identified 3918 upregulated and 2415 downregulated genes in the spleen and 231 upregulated and 65 downregulated genes in the bursa of Fabricius. We confirmed that several core genes related to immune and metabolic pathways were activated by AFB1. Furthermore, 42 and 19 differentially expressed miRNAs were found in the spleen and the bursa of Fabricius, respectively. Differentially expressed genes and target genes of differentially expressed miRNAs were mainly associated with cancer progression and immune response. The predicted mRNA-miRNA pathway network illustrated the potential regulatory mechanisms. The present study identified the transcriptional profiles and revealed potential mRNA-miRNA pathway crosstalk. This genetic regulatory network will facilitate the understanding of the immunotoxicity mechanisms of chicken immune organs induced by high concentrations of AFB1.

Antitumor Activity of Simvastatin in Preclinical Models of Mantle Cell Lymphoma

BACKGROUND

Mantle cell lymphoma (MCL) is a rare and aggressive subtype of B-cell non-Hodgkin lymphoma that remains incurable with standard therapy. Statins are well-tolerated, inexpensive, and widely prescribed as cholesterol-lowering agents to treat hyperlipidemia and to prevent cardiovascular diseases through the blockage of the mevalonate metabolic pathway. These drugs have also shown promising anti-cancer activity through pleiotropic effects including the induction of lymphoma cell death. However, their potential use as anti-MCL agents has not been evaluated so far.

AIM

The present study aimed to investigate the activity of simvastatin on MCL cells.

METHODS

We evaluated the cytotoxicity of simvastatin in MCL cell lines by CellTiter-Glo and lactate dehydrogenase (LDH) release assays. Cell proliferation and mitotic index were assessed by direct cell recounting and histone H3-pSer10 immunostaining. Apoptosis induction and reactive oxygen species (ROS) generation were evaluated by flow cytometry. Cell migration and invasion properties were determined by transwell assay. The antitumoral effect of simvastatin in vivo was evaluated in a chick embryo chorioallantoic membrane (CAM) MCL xenograft model.

RESULTS

We show that treatment with simvastatin induced a 2 to 6-fold LDH release, inhibited more than 50% of cell proliferation, and enhanced the caspase-independent ROS-mediated death of MCL cells. The effective impairment of MCL cell survival was accompanied by the inhibition of AKT and mTOR phosphorylation. Moreover, simvastatin strongly decreased MCL cell migration and invasion ability, leading to a 55% tumor growth inhibition and a consistent diminution of bone marrow and spleen metastasis in vivo.

CONCLUSION

Altogether, these data provide the first preclinical insight into the effect of simvastatin against MCL cells, suggesting that this agent might be considered for repurpose as a precise MCL therapy.

L’embryon de poule

Le développement de drogues anti-cancéreuses à visée thérapeutique nécessite leur évaluation. Ces drogues candidates sont généralement testées in vitro, sur des lignées cellulaires ou sur des cellules isolées à partir de patients, et, in vivo, dans des modèles de xénogreffe chez la souris immunodéprimée. Depuis quelques années, les contraintes réglementaires (règle des 3R : réduire, raffiner, remplacer) imposent de mettre en place des modèles alternatifs qui se substituent aux modèles murins ou, au moins, en limitent l’utilisation. Parmi les modèles alternatifs proposés, la greffe sur membrane chorio-allantoïdienne d’embryon de poule semble performante. Elle permet de suivre et de quantifier la croissance tumorale et d’autres paramètres associés, comme la néo-angiogenèse, l’invasion et la migration tumorales. Elle permet aussi le criblage de drogues. Ce modèle semble également adapté à la médecine personnalisée en cancérologie. Nous présentons dans cette revue la technique et ses avantages.

In ovo model in cancer research and tumor immunology

Considering cancer not only as malignant cells on their own but as a complex disease in which tumor cells interact and communicate with their microenvironment has motivated the establishment of clinically relevant 3D models in past years. Technological advances gave rise to novel bioengineered models, improved organoid systems, and microfabrication approaches, increasing scientific importance in preclinical research. Notwithstanding, mammalian in vivo models remain closest to mimic the patient’s situation but are limited by cost, time, and ethical constraints. Herein, the in ovo model bridges the gap as an advanced model for basic and translational cancer research without the need for ethical approval. With the avian embryo being a naturally immunodeficient host, tumor cells and primary tissues can be engrafted on the vascularized chorioallantoic membrane (CAM) with high efficiencies regardless of species-specific restrictions. The extraembryonic membranes are connected to the embryo through a continuous circulatory system, readily accessible for manipulation or longitudinal monitoring of tumor growth, metastasis, angiogenesis, and matrix remodeling. However, its applicability in immunoncological research is largely underexplored. Dual engrafting of malignant and immune cells could provide a platform to study tumor-immune cell interactions in a complex, heterogenic and dynamic microenvironment with high reproducibility. With some caveats to keep in mind, versatile methods for in and ex ovo monitoring of cellular and molecular dynamics already established in ovo are applicable alike. In this view, the present review aims to emphasize and discuss opportunities and limitations of the chicken embryo model for pre-clinical research in cancer and cancer immunology.

The Comparative Experimental Study of Sodium and Magnesium Dichloroacetate Effects on Pediatric PBT24 and SF8628 Cell Glioblastoma Tumors Using a Chicken Embryo Chorioallantoic Membrane Model and on Cells In Vitro

In this study, pyruvate dehydrogenase kinase-1 inhibition with dichloroacetate (DCA) was explored as an alternative cancer therapy. The study’s aim was to compare the effectiveness of NaDCA and MgDCA on pediatric glioblastoma PBT24 and SF8628 tumors and cells. The treatment effects were evaluated on xenografts growth on a chicken embryo chorioallantoic membrane. The PCNA, EZH2, p53, survivin expression in tumor, and the SLC12A2, SLC12A5, SLC5A8, CDH1, and CDH2 expression in cells were studied. The tumor groups were: control, cells treated with 10 mM and 5 mM of NaDCA, and 5 mM and 2.5 mM of MgDCA. The cells were also treated with 3 mM DCA. Both the 10 mM DCA preparations significantly reduced PBT24 and SF8624 tumor invasion rates, while 5 mM NaDCA reduced it only in the SF8628 tumors. The 5 mM MgDCA inhibited tumor-associated neoangiogenesis in PBT24; both doses of NaDCA inhibited tumor-associated neoangiogenesis in SF8628. The 10 mM DCA inhibited the expression of markers tested in PBT24 and SF8628 tumors, but the 5 mM DCA affect on their expression depended on the cation. The DCA treatment did not affect the SLC12A2, SLC12A5, and SLC5A8 expression in cells but increased CDH1 expression in SF8628. The tumor response to DCA at different doses indicated that a contrast between NaDCA and MgDCA effectiveness reflects the differences in the tested cells’ biologies.