Oral Immunization Against Candidiasis Using Lactobacillus casei Displaying Enolase 1 from Candida albicans

Advancing Vaccine Strategies against Candida Infections: Exploring New Frontiers

Candida albicans, along with several non-albicans Candida species, comprise a prominent fungal pathogen in humans, leading to candidiasis in various organs. The global impact of candidiasis in terms of disease burden, suffering, and fatalities is alarmingly high, making it a pressing global healthcare concern. Current treatment options rely on antifungal drugs such as azoles, polyenes, and echinocandins but are delimited due to the emergence of drug-resistant strains and associated adverse effects. The current review highlights the striking absence of a licensed antifungal vaccine for human use and the urgent need to shift our focus toward developing an anti-Candida vaccine. A number of factors affect the development of vaccines against fungal infections, including the host, intraspecies and interspecies antigenic variations, and hence, a lack of commercial interest. In addition, individuals with a high risk of fungal infection tend to be immunocompromised, so they are less likely to respond to inactivated or subunit whole organisms. Therefore, it is pertinent to discover newer and novel alternative strategies to develop safe and effective vaccines against fungal infections. This review article provides an overview of current vaccination strategies (live attenuated, whole-cell killed, subunit, conjugate, and oral vaccine), including their preclinical and clinical data on efficacy and safety. We also discuss the mechanisms of immune protection against candidiasis, including the role of innate and adaptive immunity and potential biomarkers of protection. Challenges, solutions, and future directions in vaccine development, namely, exploring novel adjuvants, harnessing the trained immunity, and utilizing immunoinformatics approaches for vaccine design and development, are also discussed. This review concludes with a summary of key findings, their implications for clinical practice and public health, and a call to action for continued investment in candidiasis vaccine research.

Utilization of Macroalgae for the Production of Bioactive Compounds and Bioprocesses Using Microbial Biotechnology

To achieve sustainable development, alternative resources should replace conventional resources such as fossil fuels. In marine ecosystems, many macroalgae grow faster than terrestrial plants. Macroalgae are roughly classified as green, red, or brown algae based on their photosynthetic pigments. Brown algae are considered to be a source of physiologically active substances such as polyphenols. Furthermore, some macroalgae can capture approximately 10 times more carbon dioxide from the atmosphere than terrestrial plants. Therefore, they have immense potential for use in the environment. Recently, macroalgae have emerged as a biomass feedstock for bioethanol production owing to their low lignin content and applicability to biorefinery processes. Herein, we provided an overview of the bioconversion of macroalgae into bioactive substances and biofuels using microbial biotechnology, including engineered yeast designed using molecular display technology.

Progress of Molecular Display Technology Using Saccharomyces cerevisiae to Achieve Sustainable Development Goals

In the long history of microorganism use, yeasts have been developed as hosts for producing biologically active compounds or for conventional fermentation. Since the introduction of genetic engineering, recombinant proteins have been designed and produced using yeast or bacterial cells. Yeasts have the unique property of expressing genes derived from both prokaryotes and eukaryotes. Saccharomyces cerevisiae is one of the well-studied yeasts in genetic engineering. Recently, molecular display technology, which involves a protein-producing system on the yeast cell surface, has been established. Using this technology, designed proteins can be displayed on the cell surface, and novel abilities are endowed to the host yeast strain. This review summarizes various molecular yeast display technologies and their principles and applications. Moreover, S. cerevisiae laboratory strains generated using molecular display technology for sustainable development are described. Each application of a molecular displayed yeast cell is also associated with the corresponding Sustainable Development Goals of the United Nations.

Vaccines against candidiasis: Status, challenges and emerging opportunity

Candidiasis is a mycosis caused by opportunistic Candida species. The occurrence of fungal infections has considerably increased in the last few years primarily due to an increase in the number of immune-suppressed individuals. Alarming bloodstream infections due to Candida sp. are associated with a higher rate of morbidity and mortality, and are emerged as major healthcare concerns worldwide. Currently, chemotherapy is the sole available option for combating fungal diseases. Moreover, the emergence of resistance to these limited available anti-fungal drugs has further accentuated the concern and highlighted the need for early detection of fungal infections, identification of novel antifungal drug targets, and development of effective therapeutics and prophylactics. Thus, there is an increasing interest in developing safe and potent immune-based therapeutics to tackle fungal diseases. In this context, vaccine design and its development have a priority. Nonetheless, despite significant advances in immune and vaccine biology over time, a viable commercialized vaccine remains awaited against fungal infections. In this minireview, we enumerate various concerted efforts made till date towards the development of anti-Candida vaccines, an option with pan-fugal vaccine, vaccines in the clinical trial, challenges, and future opportunities.

Construction of HGF-Displaying Yeast by Cell Surface Engineering

Hepatocyte growth factor (HGF) has been investigated as a regulator for immune reactions caused by transplantation and autoimmune diseases and other biological functions. Previous studies demonstrated that cDNA-encoding HGF administration could inhibit acute graft-versus-host disease (GVHD) after treatment via hematopoietic stem cell transplantation. This study aimed to show the preparation of HGF protein on yeast cell surfaces to develop a tool for the oral administration of HGF to a GVHD mouse model. In this study, full-length HGF and the heavy chain of HGF were genetically fused with α-agglutinin and were successfully displayed on the yeast cell surface. This study suggested that yeast cell surface display engineering could provide a novel administration route for HGF.

Targeting Unconventional Pathways in Pursuit of Novel Antifungals

The impact of invasive fungal infections on human health is a serious, but largely overlooked, public health issue. Commonly affecting the immunocompromised community, fungal infections are predominantly caused by species of Candida, Cryptococcus, and Aspergillus. Treatments are reliant on the aggressive use of pre-existing antifungal drug classes that target the fungal cell wall and membrane. Despite their frequent use, these drugs are subject to unfavorable drug-drug interactions, can cause undesirable side-effects and have compromised efficacy due to the emergence of antifungal resistance. Hence, there is a clear need to develop novel classes of antifungal drugs. A promising approach involves exploiting the metabolic needs of fungi by targeted interruption of essential metabolic pathways. This review highlights potential antifungal targets including enolase, a component of the enolase-plasminogen complex, and enzymes from the mannitol biosynthesis and purine nucleotide biosynthesis pathways. There has been increased interest in the enzymes that comprise these particular pathways and further investigation into their merits as antifungal targets and roles in fungal survival and virulence are warranted. Disruption of these vital processes by targeting unconventional pathways with small molecules or antibodies may serve as a promising approach to discovering novel classes of antifungals.

Advances in Oral Subunit Vaccine Design

Many pathogens invade the host at the intestinal surface. To protect against these enteropathogens, the induction of intestinal secretory IgA (SIgA) responses is paramount. While systemic vaccination provides strong systemic immune responses, oral vaccination is the most efficient way to trigger protective SIgA responses. However, the development of oral vaccines, especially oral subunit vaccines, is challenging due to mechanisms inherent to the gut. Oral vaccines need to survive the harsh environment in the gastrointestinal tract, characterized by low pH and intestinal proteases and need to reach the gut-associated lymphoid tissues, which are protected by chemical and physical barriers that prevent efficient uptake. Furthermore, they need to surmount default tolerogenic responses present in the gut, resulting in suppression of immunity or tolerance. Several strategies have been developed to tackle these hurdles, such as delivery systems that protect vaccine antigens from degradation, strong mucosal adjuvants that induce robust immune responses and targeting approaches that aim to selectively deliver vaccine antigens towards specific immune cell populations. In this review, we discuss recent advances in oral vaccine design to enable the induction of robust gut immunity and highlight that the development of next generation oral subunit vaccines will require approaches that combines these solutions.

Moonlighting Proteins at the Candidal Cell Surface

The cell wall in Candida albicans is not only a tight protective envelope but also a point of contact with the human host that provides a dynamic response to the constantly changing environment in infection niches. Particularly important roles are attributed to proteins exposed at the fungal cell surface. These include proteins that are stably and covalently bound to the cell wall or cell membrane and those that are more loosely attached. Interestingly in this regard, numerous loosely attached proteins belong to the class of “moonlighting proteins” that are originally intracellular and that perform essentially different functions in addition to their primary housekeeping roles. These proteins also demonstrate unpredicted interactions with non-canonical partners at an a priori unexpected extracellular location, achieved via non-classical secretion routes. Acting both individually and collectively, the moonlighting proteins contribute to candidal virulence and pathogenicity through their involvement in mechanisms critical for successful host colonization and infection, such as the adhesion to host cells, interactions with plasma homeostatic proteolytic cascades, responses to stress conditions and molecular mimicry. The documented knowledge of the roles of these proteins in C. albicans pathogenicity has utility for assisting the design of new therapeutic, diagnostic and preventive strategies against candidiasis.

Difficult but Not Impossible: in Search of an Anti-Candida Vaccine

Purpose of Review

Pervasive fungal infection among the immunocompromised population, in conjunction with a lack of effective treatment options, has demanded further scrutiny. Millions of people are still dying annually from fungal infections. While existing treatment for these fungal infections exists, it is difficult to administer without adverse effects in the immunocompromised and is slowly becoming obsolete due to varying mutation rates and rising resistance in multiple species. Thus, vaccines may be a viable target for preventing and treating fungal infections and addressing the critical challenge of such infections.

Recent Findings

Candida albicans, along with other non-albicans Candida species, is among the more virulent class of fungal specimens considered for vaccine development. C. albicans is responsible for a large percentage of invasive fungal infections among immunocompromised and immunocompetent populations and carries a relatively high mortality rate. In the last decade, a recent increase in infective capacity among Candida species has shed light on the lack of adequate fungal vaccine choices. While roadblocks still exist in the development of antifungal vaccines, several novel targets have been examined and proposed as candidates.

Summary

Success in vaccine development has universal appeal; an anti-Candida vaccine formulation could be modified to work against other fungal infections and thus bolster the antifungal pipeline.

Molecular and Physiological Study of Candida albicans by Quantitative Proteome Analysis

Candida albicans is one of the major pathogens that cause the serious infectious condition known as candidiasis. C. albicans was investigated by proteome analysis to systematically examine its virulence factors and to promote the development of novel pharmaceuticals against candidiasis. Here, we review quantitative time-course proteomics data related to C. albicans adaptation to fetal bovine serum, which were obtained using a nano-liquid chromatography/tandem mass spectrometry system equipped with a long monolithic silica capillary column. It was revealed that C. albicans induced proteins involved in iron acquisition, detoxification of oxidative species, energy production, and pleiotropic stress tolerance. Native interactions of C. albicans with macrophages were also investigated with the same proteome-analysis system. Simultaneous analysis of C. albicans and macrophages without isolating individual living cells revealed an attractive strategy for studying the survival of C. albicans. Although those data were obtained by performing proteome analyses, the molecular physiology of C. albicans is discussed and trials related to pharmaceutical applications are also examined.

Moonlighting proteins induce protection in a mouse model against Candida species

In recent years, C. albicans and C. glabrata have been identified as the main cause of candidemia and invasive candidiasis in hospitalized and immunocompromised patients. In order to colonize the human host, these fungi express several virulence factors such as the response to oxidative stress and the formation of biofilms. In the expression of these virulence factors, the cell wall of C. albicans and C. glabrata is of fundamental importance. As the outermost structure of the yeast, the cell wall is the first to come in contact with the reactive oxygen species (ROS) generated during the respiratory outbreak, and in the formation of biofilms, it is the first to adhere to organs or medical devices implanted in the human host. In both processes, several cell wall proteins (CWP) are required, since they promote attachment to human cells or abiotic surfaces, as well as to detoxify ROS. In our working group we have identified moonlighting CWP in response to oxidative stress as well as in the formation of biofilms. Having identified moonlighting CWP in Candida species in response to two virulence factors indicates that these proteins may possibly be immunodominant. The aim of the present work was to evaluate whether proteins of this type such as fructose-bisphosphate aldolase (Fba1), phosphoglycerate kinase (Pgk) and pyruvate kinase (Pk), could confer protection in a mouse model against C. albicans and C. glabrata. For this, recombinant proteins His₆-Fba1, His₆-Pgk and His₆-Pk were constructed and used to immunize several groups of mice. The immunized mice were infected with C. albicans or C. glabrata, and subsequently the liver, spleen and kidney were extracted and the number of CFU was determined. Our results showed that Pk confers immunity to mice against C. albicans, while Fba1 to C. glabrata. This data allows us to conclude that the moonlighting CWP, Fba1 and Pk confer in vivo protection in a specific way against each species of Candida. This makes them promising candidates for developing specific vaccines against these pathogens.

Live bacterial vaccine vector and delivery strategies of heterologous antigen: A review

Live bacteria, including attenuated bacteria and probiotics, can be engineered to deliver target antigen to excite the host immune system. The preponderance of these live bacterial vaccine vectors is that they can stimulate durable humoral and cellular immunity. Moreover, delivery strategies of heterologous antigen in live bacterial promote the applications of new vaccine development. Genetic technologies are evolving, which potentiate the developing of heterologous antigen delivery systems, including bacterial surface display system, bacterial secretion system and balanced lethal vector system. Although the live bacterial vaccine vector is a powerful adjuvant, certain disadvantages, such as safety risk, must also be taken into account. In this review, we compare the development of representative live bacterial vectors, and summarize the main characterizations of the various delivery strategies of heterologous antigen in live vector vaccines.

Preparation of an Oral Vaccine by Proteome Analysis and Molecular Display Technology

In recent years, genetic engineering and protein expression technologies have promoted the development of recombinant protein vaccines. To accelerate the development of efficient vaccines for mycosis, screening candidate antigens, and determining the optimal route of administration are indispensable steps. Two methods for identifying novel antigens and producing antigens specific to Candida albicans, as a model causative pathogen of mycosis, are discussed in this chapter. Specifically, the application of liquid chromatography/tandem mass spectrometry using a long monolithic column for proteome analysis to identify virulence factors of C. albicans, followed by molecular display technology to produce an oral vaccine using antigens found by the proteomic study, is described.

Lactobacillus rhamnosus inhibits Candida albicans virulence factors in vitro and modulates immune system in Galleria mellonella

AIM

The aim of this study was to evaluate the potential anti-Candida effects of Lactobacillus rhamnosus ATCC 9595 on Candida albicans ATCC 18804 using in vitro and in vivo models.

METHODS AND RESULTS

The in vitro analysis evaluated the effects of L. rhamnosus on C. albicans's biofilm formation by CFU count and metabolic activity, filamentation capacity, and adhesion (ALS3 and HWP1) and transcriptional regulatory gene (BCR1 and CPH1) expression. The in vitro results showed that both the L. rhamnosus cells and supernatant reduced C. albicans biofilm formation, filamentation and gene expression. In the in vivo study, the treatment with L. rhamnosus supernatant increased 80% the survival of Galleria mellonella larvae infected with C. albicans. Furthermore, the supernatant of L. rhamnosus recruited haemocytes into the haemolymph (2·1-fold increase).

CONCLUSIONS

Lactobacillus rhamnosus reduced the biofilm formation and filamentation of C. albicans in vitro by negatively regulating all studied C. albicans genes. Lactobacillus rhamnosus protected G. mellonella against experimental candidiasis in vivo.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study is the first study to report the anti-Candida properties of L. rhamnosus ATCC 9595. The supernatant of this strain has immunomodulatory effects on the G. mellonella model and protects the larvae against pathogens.

Oral Vaccine Development by Molecular Display Methods Using Microbial Cells

Oral vaccines are easier to administer than injectable vaccines. To induce an adequate immune response using vaccines, antigenic proteins are usually combined with adjuvant materials. This chapter presents methodologies for the design of oral vaccines using molecular display technology. In molecular display technology, antigenic proteins are displayed on a microbial cell surface with adjuvant ability. This technology would provide a quite convenient process to produce oral vaccines when the DNA sequence of an efficient antigenic protein is available. As an example, oral vaccines against candidiasis were introduced using two different molecular display systems with Saccharomyces cerevisiae and Lactobacillus casei.

Immunomodulatory effects of Lactobacillus strains: emphasis on their effects on cancer cells

Lactobacilli are a group of normal microbiota whose immunomodulatory effects have been known for a long time. Recently, they have gained more attention for their direct and indirect effects on cancer cells. Several cell line experiments, animal model studies as well as clinical trials have indicated their inhibitory effects on cancer initiation and progression. Different lactobacilli strains could modulate innate and adoptive immune system. Such effects have been documented in modulation of function of T cells, dendritic cells and macrophages as well as cytokine production. In this review, the various immunomodulatory effects of lactobacilli on tumor cells as well as their direct cytotoxic effects on cancer cells are discussed.