Heat treatment improves antigen-specific T cell activation after protein delivery by several but not all yeast genera

RNA Vaccines: Yeast as a Novel Antigen Vehicle

In the last decades, technological advances for RNA manipulation enabled and expanded its application in vaccine development. This approach comprises synthetic single-stranded mRNA molecules that direct the translation of the antigen responsible for activating the desired immune response. The success of RNA vaccines depends on the delivery vehicle. Among the systems, yeasts emerge as a new approach, already employed to deliver protein antigens, with efficacy demonstrated through preclinical and clinical trials. β-glucans and mannans in their walls are responsible for the adjuvant property of this system. Yeast β-glucan capsules, microparticles, and nanoparticles can modulate immune responses and have a high capacity to carry nucleic acids, with bioavailability upon oral immunization and targeting to receptors present in antigen-presenting cells (APCs). In addition, yeasts are suitable vehicles for the protection and specific delivery of therapeutic vaccines based on RNAi. Compared to protein antigens, the use of yeast for DNA or RNA vaccine delivery is less established and has fewer studies, most of them in the preclinical phase. Here, we present an overview of the attributes of yeast or its derivatives for the delivery of RNA-based vaccines, discussing the current challenges and prospects of this promising strategy.

Standardization and Key Aspects of the Development of Whole Yeast Cell Vaccines

In the context of vaccine development, improving antigenic presentation is critical for the activation of specific immune responses and the success of immunization, in addition to selecting an appropriate target. In this sense, different strategies have been developed and improved. Among them is the use of yeast cells as vehicles for the delivery of recombinant antigens. These vaccines, named whole yeast vaccines (WYVs), can induce humoral and cellular immune responses, with the additional advantage of dispensing with the use of adjuvants due to the immunostimulatory properties of their cell wall components. However, there are some gaps in the methodologies for obtaining and validating recombinant strains and vaccine formulations. The standardization of these parameters is an important factor for WYVs approval by regulatory agencies and, consequently, their licensing. This review aimed to provide an overview of the main parameters to consider when developing a yeast-based vaccine, addressing some available tools, and highlighting the main variables that can influence the vaccine production process.

Effect of 1,3-Beta Glucans Dietary Addition on the Growth, Intestinal Histology, Blood Biochemical Parameters, Immune Response, and Immune Expression of CD3 and CD20 in Broiler Chickens

This experiment evaluated the impact of the dietary addition of 1,3-β-glucans (GLU) on broiler chickens’ growth, intestinal histology, blood biochemical parameters, and immunity. Two hundred three-day-old male broilers (Ross 308) (97.93 ± 0.19 g/chick) were randomly assigned into four treatments with five replicates, each containing ten birds, in a complete randomized design. The four treatments were formulated with 0, 50, 100, and 150 mg 1,3-β-glucans kg−1 in broiler chicken diets. During the study, no significant impacts (p > 0.05) were observed in weight gain and feed conversion ratio (FCR) between treatment groups. Based on the results of total body weight gain and FCR, the optimal level of 1,3-β-glucan is 120 mg Kg−1. The intestinal histomorphology was improved by GLU supplementation, as indicated by increased villi height and villi height to crypt depth ratio (p < 0.01). All levels of supplemental β-1,3 glucan decreased the serum total cholesterol (TC), triglyceride levels, and low-density lipoprotein cholesterol (LDL-C) (p < 0.05). The serum levels of growth hormones (GH), triiodothyronine (T3), and thyroxine (T4) were increased in GLU-supplemented groups (p < 0.05). The serum immune indices (lysozyme activity, interleukin 10 (IL10), complement 3 (C3), and total protein levels) were increased in the GLU-supplemented groups (p < 0.05). Dietary GLU up-regulated the immunoexpression of CD3 (T-cell marker) and CD20 (B-cell marker) in the spleen of birds (p < 0.01). It can be concluded that 1,3-β-glucan can be added to broiler chicken diets for improving the development and integrity of the intestine and enhancing the bird’s immune status. The optimal level for 1,3-β-glucan dietary supplementation was 120 mg Kg−1. Dietary 1,3-β-glucan has a hypolipidemic effect and improves the hormonal profile of birds without affecting their growth rate.

Genomic features, aroma profiles, and probiotic potential of the Debaryomyces hansenii species complex strains isolated from Korean soybean fermented food

Fermented soybean products are gaining attention in the food industry owing to their nutritive value and health benefits. In this study, we performed genomic analysis and physiological characterization of two Debaryomyces spp. yeast isolates obtained from a Korean traditional fermented soy sauce "ganjang". Both Debaryomyces hansenii ganjang isolates KD2 and C11 showed halotolerance to concentrations of up to 15% NaCl and improved growth in the presence of salt. Ploidy and whole-genome sequencing analyses indicated that the KD2 genome is haploid, whereas the C11 genome is heterozygous diploid with two distinctive subgenomes. Interestingly, phylogenetic analysis using intron sequences indicated that the C11 strain was generated via hybridization between D. hansenii and D. tyrocola ancestor strains. The D. hansenii KD2 and D. hansenii-hybrid C11 produced various volatile flavor compounds associated with butter, caramel, cheese, and fruits, and showed high bioconversion activity from ferulic acid to 4-vinylguaiacol, a characteristic flavor compound of soybean products. Both KD2 and C11 exhibited viability in the presence of bile salts and at low pH and showed immunomodulatory activity to induce high levels of the anti-inflammatory cytokine IL-10. The safety of the yeast isolates was confirmed by analyzing virulence and acute oral toxicity. Together, the D. hansenii ganjang isolates possess physiological properties beneficial for improving the flavor and nutritional value of fermented products.

Yeast as carrier for drug delivery and vaccine construction

Yeast has been employed as an effective derived drug carrier as a unicellular microorganism. Many research works have been devoted to the encapsulation of nucleic acid compounds, insoluble small molecule drugs, small molecules, liposomes, polymers, and various nanoparticles in yeast for the treatment of disease. Recombinant yeast-based vaccine carriers (WYV) have played a major role in the development of vaccines. Herein, the latest reports on the application of yeast carriers and the development of related research are summarized, a conceptual description of gastrointestinal absorption of yeast carriers, as well as the various package forms of different drug molecules and nanoparticles in yeast carriers are introduced. In addition, the advantages and development of recombinant yeast vaccine carriers for the disease, veterinary and aquaculture applications are discussed. Moreover, the current challenges and future directions of yeast carriers are proposed.

A Novel Whole Yeast-Based Subunit Oral Vaccine Against Eimeria tenella in Chickens

Cheap, easy-to-produce oral vaccines are needed for control of coccidiosis in chickens to reduce the impact of this disease on welfare and economic performance. Saccharomyces cerevisiae yeast expressing three Eimeria tenella antigens were developed and delivered as heat-killed, freeze-dried whole yeast oral vaccines to chickens in four separate studies. After vaccination, E. tenella replication was reduced following low dose challenge (250 oocysts) in Hy-Line Brown layer chickens (p<0.01). Similarly, caecal lesion score was reduced in Hy-Line Brown layer chickens vaccinated using a mixture of S. cerevisiae expressing EtAMA1, EtIMP1 and EtMIC3 following pathogenic-level challenge (4,000 E. tenella oocysts; p<0.01). Mean body weight gain post-challenge with 15,000 E. tenella oocysts was significantly increased in vaccinated Cobb500 broiler chickens compared to mock-vaccinated controls (p<0.01). Thus, inactivated recombinant yeast vaccines offer cost-effective and scalable opportunities for control of coccidiosis, with relevance to broiler production and chickens reared in low-and middle-income countries (LMICs).

Yeasts as a promising delivery platform for DNA and RNA vaccines

Yeasts are considered a useful system for the development of vaccines for human and veterinary health. Species such as Saccharomyces cerevisiae and Pichia pastoris have been used successfully as host organisms for the production of subunit vaccines. These organisms have been also explored as vaccine vehicles enabling the delivery of antigens such as proteins and nucleic acids. The employed species possess a GRAS status (Generally Recognized as Safe) for the production of therapeutic proteins, besides promoting immunostimulation due to the properties of their wall cell composition. This strategy allows the administration of nucleic acids orally and a specific delivery to professional antigen-presenting cells (APCs). In this review, we seek to outline the development of whole yeast vaccines (WYV) carrying nucleic acids in different approaches in the medical field, as well as the immunological aspects of this vaccine strategy. The data presented here reveal the application of this platform in promoting effective immune responses in the context of prophylactic and therapeutic approaches.

Structure, preparation, modification, and bioactivities of β-glucan and mannan from yeast cell wall: A review

In order to solve the antibiotic resistance, the research on antibiotic substitutes has received an extensive attention. Many studies have shown that β-glucan and mannan from yeast cell wall have the potential to replace antibiotics for the prevention and treatment of animal diseases, thereby reducing the development and spread of antibiotic-resistant bacterial pathogens. β-Glucan and mannan had a variety of biological functions, including improving the intestinal environment, stimulating innate and acquired immunity, adsorbing mycotoxins, enhancing antioxidant capacity, and so on. The biological activities of β-glucan and mannan can be improved by chemically modifying its primary structure or reducing molecular weight. In this paper, the structure, preparation, modification, and biological activities of β-glucan and mannan were reviewed, which provided future perspectives of β-glucan and mannan.

Conjugation of β-glucans on heat-stable enterotoxin (ST) to enhance the immunogenic response in mouse leucocytes

Enterotoxigenic Escherichia coli (ETEC) is an important diarrhea-causing pathogen for humans. Heat-stable enterotoxin (ST) plays a crucial role in triggering diarrhea and ETEC pathogenesis. However, ST is a small peptide that lacks immunogenic activity itself but becomes immunogenic when it is coupled to a carrier molecule. In this study, the β-glucans (BG) from yeasts have been used to test their immunomodulatory activity and adjuvant effect on the properties of ST. This study aimed to synthesize and characterize a conjugate of yeast-derived β-glucan with the ST enterotoxin (BG-ST) and evaluate the antigenic and antioxidant activities in mouse splenocytes. Fourier transform infrared spectroscopy and scanning electron microscopy analysis showed new bands and changes in morphology, respectively, confirming ST was successfully coupled to beta glucan. Additionally, according to the enzyme-linked immunosorbent assay (ELISA), conjugation efficiency was almost 90%. Cellular viability, phagocytic cell proportion, and respiratory burst enhanced splenocytes stimulated by BG-ST. In addition, nitric oxide production and antioxidant enzymes increased in cells stimulated with BG-ST, BG and ST. In conclusion, the results revealed the successful conjugation of β-glucan with ST peptide enhancing immune and antioxidant parameters to a greater extent than their individual components.

Development of Fish Immunity and the Role of β-Glucan in Immune Responses

Administration of β-glucans through various routes, including immersion, dietary inclusion, or injection, have been found to stimulate various facets of immune responses, such as resistance to infections and resistance to environmental stress. β-Glucans used as an immunomodulatory food supplement have been found beneficial in eliciting immunity in commercial aquaculture. Despite extensive research involving more than 3000 published studies, knowledge of the receptors involved in recognition of β-glucans, their downstream signaling, and overall mechanisms of action is still lacking. The aim of this review is to summarize and discuss what is currently known about of the use of β-glucans in fish.

Targeted delivery of functionalized PLGA nanoparticles to macrophages by complexation with the yeast Saccharomyces cerevisiae

Nanoparticles (NPs) are able to deliver a variety of substances into eukaryotic cells. However, their usage is often hampered by a lack of specificity, leading to the undesired uptake of NPs by virtually all cell types. In contrast to this, yeast is known to be specifically taken up into immune cells after entering the body. Therefore, we investigated the interaction of biodegradable surface-modified poly(lactic-co-glycolic acid) (PLGA) particles with yeast cells to overcome the unspecificity of the particulate carriers. Cells of different Saccharomyces cerevisiae strains were characterized regarding their interaction with PLGA-NPs under isotonic and hypotonic conditions. The particles were shown to efficiently interact with yeast cells leading to stable NP/yeast-complexes allowing to associate or even internalize compounds. Notably, applying those complexes to a coculture model of HeLa cells and macrophages, the macrophages were specifically targeted. This novel nano-in-micro carrier system suggests itself as a promising tool for the delivery of biologically active agents into phagocytic cells combining specificity and efficiency.

β-glucans as potential immunoadjuvants: A review on the adjuvanticity, structure-activity relationship and receptor recognition properties

β-glucans, a group of polysaccharides exist in many organism species such as mushrooms, yeasts, oats, barley, seaweed, but not mammalians, have a variety of biological activities and applications in drugs and other healthcare products. In recent years, β-glucans have been studied as adjuvants in anti-infection vaccines as well as immunomodulators in anti-cancer immunotherapy. β-glucans can regulate immune responses when administered alone and can connect innate and adaptive immunity to improve immunogenicity of vaccines. When β-glucans act as immunostimulants or adjuvants, a set of receptors have been revealed to recognize β-glucans, including dectin-1, complement receptor 3 (CR3), CD5, lactosylceramide, and so on. Therefore, this review is mainly focused on the application of β-glucans as immune adjuvants, the receptors of β-glucans, as well as their structure and activity relationship which will benefit future research of β-glucans.