Transcutaneous immunization with Clostridium difficile toxoid A induces systemic and mucosal immune responses and toxin A-neutralizing antibodies in mice

Clostridioides difficile Infection: A Clinical Review of Pathogenesis, Clinical Considerations, and Treatment Strategies

BACKGROUND

Clostridioides difficile infection (CDI) is a common nosocomial infection. Risk factors for developing CDI include prior hospitalization, being older than 65 years old, antibiotic use, and chronic disease. It is linked with diarrhea and colitis and can vary in severity. It is a major cause of increased morbidity and mortality among hospitalized patients. However, community-acquired CDI is also increasing. Proper diagnosis and determination of severity are crucial for the treatment of CDI. Depending on how severe the CDI is, the patient may endorse different symptoms and physical exam findings. The severity of CDI will determine how aggressively it is treated. Management and treatment: Laboratory studies can be helpful in the diagnosis of CDI. In this regard, common labs include complete blood count, stool assays, and, in certain cases, radiography and endoscopy. Mild-to-moderate colitis is treated with antibiotics, but severe colitis requires a different approach, which may include surgery. Several alternative therapies for CDI exist and have shown promising results. This review will touch upon these therapies, which include fecal transplants, intravenous immunoglobulin, and the use of cholestyramine and tigecycline.

CONCLUSION

Prevention of CDI can be achieved by proper hygiene, vaccinations, and detecting the infection early. Proper hygiene is indeed noted to be one of the best ways to prevent CDI in the hospital setting. Overprescribing antibiotics is also another huge reason why CDI occurs. Proper prescription of antibiotics can also help reduce the chances of acquiring CDI.

Major pathogenic Clostridia in human and progress toward the clostridial vaccines

The Clostridium genus is composed of a large spectrum of heterogeneous bacteria. They are Gram-positive, mostly mesophilic, and anaerobic spore-forming strains. Clostridia are widely distributed in oxygen-free habitats. They are found principally in the soil and intestines of ruminants as normal flora, but also are the cause of several infections in humans. The infections produced by important species in humans include botulism, tetanus, pseudomembranous colitis, antibiotics-associated diarrhea, and gas gangrene. Immunization with toxoid or bacterin-toxoid or genetically modified or other vaccines is a protective way against clostridial infection. Several experimental or commercial vaccines have been developed worldwide. Although conventional vaccines including toxoid vaccines are very important, the new generation of vaccines is an effective alternative to conventional vaccines. Recent advances have made it possible for new vaccines to increase immunogenicity. This review discusses briefly the important species of clostridia in humans, their toxins structure, and vaccine development and usage throughout the world.

Molecular evolution of the VacA p55 binding domain of Helicobacter pylori in mestizos from a high gastric cancer region of Colombia

The stomach bacterium Helicobacter pylori is one of the most prevalent pathogens in humans, closely linked with serious diseases such as gastric cancer. The microbe has been associated with its host for more than 100,000 years and escorted modern humans out of Africa. H. pylori is predominantly transmitted within families and dispersed globally, resulting in distinct phylogeographic patterns, which can be utilized to investigate migrations and bioturbation events in human history. Latin America was affected by several human migratory waves due to the Spanish colonisation that drastically changed the genetic load and composition of the bacteria and its host. Genetic evidence indicates that independent evolutionary lines of H. pylori have evolved in mestizos from Colombia and other countries in the region during more than 500 years since colonisation. The vacuolating cytotoxin VacA represents a major virulence factor of the pathogen comprising two domains, p33 and p55, the latter of which is essential for binding to the host epithelial cell. The evolution of the VacA toxin in Colombia has been strongly biased due to the effects of Spanish colonization. However, the variation patterns and microevolution of the p55 domain have not yet been described for this population. In the present study, we determined the genetic polymorphisms and deviations in the neutral model of molecular evolution in the p55 domain of 101 clinical H. pylori isolates collected in Bogotá, a city located in Andean mountains characterized by its high gastric cancer risk and its dominant mestizo population. The microevolutionary patterns of the p55 domain were shaped by recombination, purifying and episodic diversifying positive selection. Furthermore, amino acid positions 261 and 321 in the p55 domain of VacA show a high variability among mestizos clinical subsets, suggesting that natural selection in H. pylori may operate differentially in patients with different gastric diseases.

Protective Effect of Carvacrol against Gut Dysbiosis and Clostridium difficile Associated Disease in a Mouse Model

This study investigated the effect of carvacrol (CR), a phytophenolic compound on antibiotic-associated gut dysbiosis and C. difficile infection in a mouse model. Five to six-week-old C57BL/6 mice were randomly divided into seven treatment groups (challenge and control) of eight mice each. Mice were fed with irradiated feed supplemented with CR (0, 0.05, and 0.1%); the challenge groups were made susceptible to C. difficile by orally administering an antibiotic cocktail in water and an intra-peritoneal injection of clindamycin. Both challenge and control groups were infected with 10⁵CFU/ml of hypervirulent C. difficile (ATCC 1870) spores or PBS, and observed for clinical signs for 10 days. Respective control groups for CR, antibiotics, and their combination were included for investigating their effect on mouse enteric microflora. Mouse body weight and clinical and diarrhea scores were recorded daily post infection. Fecal samples were collected for microbiome analysis using rRNA sequencing in MiSeq platform. Carvacrol supplementation significantly reduced the incidence of diarrhea and improved the clinical and diarrhea scores in mice (p < 0.05). Microbiome analysis revealed a significant increase in Proteobacteria and reduction in the abundance of protective bacterial flora in antibiotic-treated and C. difficile-infected mice compared to controls (p < 0.05). However, CR supplementation positively altered the microbiome composition, as revealed by an increased abundance of beneficial bacteria, including Firmicutes, and significantly reduced the proportion of detrimental flora such as Proteobacteria, without significantly affecting the gut microbiome diversity compared to control. Results suggest that CR could potentially be used to control gut dysbiosis and reduce C. difficile infection.

A Tetraspecific VHH-Based Neutralizing Antibody Modifies Disease Outcome in Three Animal Models of Clostridium difficile Infection

Clostridium difficile infection (CDI), a leading cause of nosocomial infection, is a serious disease in North America, Europe, and Asia. CDI varies greatly from asymptomatic carriage to life-threatening diarrhea, toxic megacolon, and toxemia. The incidence of community-acquired infection has increased due to the emergence of hypervirulent antibiotic-resistant strains. These new strains contribute to the frequent occurrence of disease relapse, complicating treatment, increasing hospital stays, and increasing morbidity and mortality among patients. Therefore, it is critical to develop new therapeutic approaches that bypass the development of antimicrobial resistance and avoid disruption of gut microflora. Here, we describe the construction of a single heteromultimeric VHH-based neutralizing agent (VNA) that targets the two primary virulence factors of Clostridium difficile, toxins A (TcdA) and B (TcdB). Designated VNA2-Tcd, this agent has subnanomolar toxin neutralization potencies for both C. difficile toxins in cell assays. When given systemically by parenteral administration, VNA2-Tcd protected against CDI in gnotobiotic piglets and mice and to a lesser extent in hamsters. Protection from CDI was also observed in gnotobiotic piglets treated by gene therapy with an adenovirus that promoted the expression of VNA2-Tcd.

Immunogenicity and protective efficacy of recombinant Clostridium difficile flagellar protein FliC

Clostridium difficile is a Gram-positive bacillus and is the leading cause of toxin-mediated nosocomial diarrhea following antibiotic use. C. difficile flagella play a role in colonization, adherence, biofilm formation, and toxin production, which might contribute to the overall virulence of certain strains. Human and animal studies indicate that anti-flagella immune responses may play a role in protection against colonization by C. difficile and subsequent disease outcome. Here we report that recombinant C. difficile flagellin (FliC) is immunogenic and protective in a murine model of C. difficile infection (CDI) against a clinical C. difficile strain, UK1. Passive protection experiments using anti-FliC polyclonal serum in mice suggest this protection to be antibody-mediated. FliC immunization also was able to afford partial protection against CDI and death in hamsters following challenge with C. difficile 630Δerm. Additionally, immunization against FliC does not have an adverse effect on the normal gut flora of vaccinated hamsters as evidenced by comparing the fecal microbiome of vaccinated and control hamsters. Therefore, the use of FliC as a vaccine candidate against CDI warrants further testing.

Immunogenicity and protective efficacy of Clostridium difficile spore proteins

Clostridium difficile is a spore-forming, anaerobic, Gram-positive organism that is the leading cause of antibiotic-associated infectious diarrhea, commonly known as C. difficile infection (CDI). C. difficile spores play an important role in the pathogenesis of CDI. Spore proteins, especially those that are surface-bound may play an essential role in the germination, colonization and persistence of C. difficile in the human gut. In our current study, we report the identification of two surface-bound spore proteins, CdeC and CdeM that may be utilized as immunization candidates against C. difficile. These spore proteins are immunogenic in mice and are able to protect mice against challenge with C. difficile UK1, a clinically-relevant 027/B1/NAP1 strain. These spore proteins are also able to afford high levels of protection against challenge with C. difficile 630Δerm in golden Syrian hamsters. This unprecedented study shows the vaccination potential of C. difficile spore exosporium proteins.

Novel therapeutic strategies for Clostridium difficile infections

INTRODUCTION

In recent years, Clostridium difficile has become the primary cause of antibiotic-associated diarrhea and pseudomembranous colitis, resulting in long and complicated hospital stays that represent a serious burden for patients as well as health care systems. Currently, conservative treatment of C. difficile infection (CDI) relies on the antibiotics vancomycin, metronidazole or fidaxomicin, or in case of multiple recurrences, fecal microbiota transplantation (FMT).

AREAS COVERED

The fast-spreading, epidemic nature of this pathogen urgently necessitates the search for alternative treatment strategies as well as antibiotic targets. Accordingly, in this review, we highlight the recent findings regarding virulence associated traits of C. difficile, evaluate their potential as alternative drug targets, and present current efforts in designing inhibitory compounds, with the aim of pointing out possibilities for future treatment strategies.

EXPERT OPINION

Increased attention on systematic analysis of the virulence mechanisms of C. difficile has already led to the identification of several alternative drug targets. In the future, applying state of the art 'omics' and the development of novel infection models that mimic the human gut, a highly complex ecological niche, will unveil the genomic and metabolic plasticity of this pathogen and will certainly help dealing with future challenges.

The host immune response to Clostridium difficile infection

Clostridium difficile infection (CDI) is the most common infectious cause of healthcare-acquired diarrhoea. Outcomes of C. difficile colonization are varied, from asymptomatic carriage to fulminant colitis and death, due in part to the interplay between the pathogenic virulence factors of the bacterium and the counteractive immune responses of the host. Secreted toxins A and B are the major virulence factors of C. difficile and induce a profound inflammatory response by intoxicating intestinal epithelial cells causing proinflammatory cytokine release. Host cell necrosis, vascular permeability and neutrophil infiltration lead to an elevated white cell count, profuse diarrhoea and in severe cases, dehydration, hypoalbuminaemia and toxic megacolon. Other bacterial virulence factors, including surface layer proteins and flagella proteins, are detected by host cell surface signal molecules that trigger downstream cell-mediated immune pathways. Human studies have identified a role for serum and faecal immunoglobulin levels in protection from disease, but the recent development of a mouse model of CDI has enabled studies into the precise molecular interactions that trigger the immune response during infection. Key effector molecules have been identified that can drive towards a protective anti-inflammatory response or a damaging proinflammatory response. The limitations of current antimicrobial therapies for CDI have led to the development of both active and passive immunotherapies, none of which have, as yet been formally approved for CDI. However, recent advances in our understanding of the molecular basis of host immune protection against CDI may provide an exciting opportunity for novel therapeutic developments in the future.

Antibodies for treatment of Clostridium difficile infection

Antibodies for the treatment of Clostridium difficile infection (CDI) have been demonstrated to be effective in the research and clinical environments. Early uncertainties about molecular and treatment modalities now appear to have converged upon the systemic dosing of mixtures of human IgG1. Although multiple examples of high-potency monoclonal antibodies (MAbs) exist, significant difficulties were initially encountered in their discovery. This minireview describes historical and contemporary MAbs and highlights differences between the most potent MAbs, which may offer insight into the pathogenesis and treatment of CDI.

Vaccines against Clostridium difficile

Clostridium difficile infection (CDI) is recognized as a major cause of nosocomial diseases ranging from antibiotic related diarrhea to fulminant colitis. Emergence during the last 2 decades of C. difficile strains associated with high incidence, severity and lethal outcomes has increased the challenges for CDI treatment. A limited number of drugs have proven to be effective against CDI and concerns about antibiotic resistance as well as recurring disease solicited the search for novel therapeutic strategies. Active vaccination provides the attractive opportunity to prevent CDI, and intense research in recent years led to development of experimental vaccines, 3 of which are currently under clinical evaluation. This review summarizes recent achievements and remaining challenges in the field of C. difficile vaccines, and discusses future perspectives in view of newly-identified candidate antigens.

Carvacrol and trans-cinnamaldehyde reduce Clostridium difficile toxin production and cytotoxicity in vitro

Clostridium difficile is a nosocomial pathogen that causes a serious toxin-mediated enteric disease in humans. Reducing C. difficile toxin production could significantly minimize its pathogenicity and improve disease outcomes in humans. This study investigated the efficacy of two, food-grade, plant-derived compounds, namely trans-cinnamaldehyde (TC) and carvacrol (CR) in reducing C. difficile toxin production and cytotoxicity in vitro. Three hypervirulent C. difficile isolates were grown with or without the sub-inhibitory concentrations of TC or CR, and the culture supernatant and the bacterial pellet were collected for total toxin quantitation, Vero cell cytotoxicity assay and RT-qPCR analysis of toxin-encoding genes. The effect of CR and TC on a codY mutant and wild type C. difficile was also investigated. Carvacrol and TC substantially reduced C. difficile toxin production and cytotoxicity on Vero cells. The plant compounds also significantly down-regulated toxin production genes. Carvacrol and TC did not inhibit toxin production in the codY mutant of C. difficile, suggesting a potential codY-mediated anti-toxigenic mechanism of the plant compounds. The antitoxigenic concentrations of CR and TC did not inhibit the growth of beneficial gut bacteria. Our results suggest that CR and TC could potentially be used to control C. difficile, and warrant future studies in vivo.

Progress in the discovery of treatments for C. difficile infection: A clinical and medicinal chemistry review

Clostridium difficile is an anaerobic, Gram-positive pathogen that causes C. difficile infection, which results in significant morbidity and mortality. The incidence of C. difficile infection in developed countries has become increasingly high due to the emergence of newer epidemic strains, a growing elderly population, extensive use of broad spectrum antibiotics, and limited therapies for this diarrheal disease. Because treatment options currently available for C. difficile infection have some drawbacks, including cost, promotion of resistance, and selectivity problems, new agents are urgently needed to address these challenges. This review article focuses on two parts: the first part summarizes current clinical treatment strategies and agents under clinical development for C. difficile infection; the second part reviews newly reported anti-difficile agents that have been evaluated or reevaluated in the last five years and are in the early stages of drug discovery and development. Antibiotics are divided into natural product inspired and synthetic small molecule compounds that may have the potential to be more efficacious than currently approved treatments. This includes potency, selectivity, reduced cytotoxicity, and novel modes of action to prevent resistance.

Protection from Clostridium difficile infection in CD4 T Cell- and polymeric immunoglobulin receptor-deficient mice

Clostridium difficile rivals methicillin-resistant Staphylococcus aureus as the primary hospital-acquired infection. C. difficile infection (CDI) caused by toxins A and/or B can manifest as mild diarrhea to life-threatening pseudomembranous colitis. Although most patients recover fully from CDI, ~20% undergo recurrent disease. Several studies have demonstrated a correlation between anti-toxin antibody (Ab) and decreased recurrence; however, the contributions of the systemic and mucosal Ab responses remain unclear. Our goal was to use the CDI mouse model to characterize the protective immune response to C. difficile. C57BL/6 mice infected with epidemic C. difficile strain BI17 developed protective immunity against CDI and did not develop CDI upon rechallenge; they generated systemic IgG and IgA as well as mucosal IgA Ab to toxin. To determine if protective immunity to C. difficile could be generated in immunodeficient individuals, we infected CD4(-/-) mice and found that they generated both mucosal and serum IgA anti-toxin Abs and were protected from CDI upon rechallenge, with protection dependent on major histocompatibility complex class II (MHCII) expression; no IgG anti-toxin Ab was found. We found that protection was likely due to neutralizing mucosal IgA Ab. In contrast, pIgR(-/-) mice, which lack the receptor to transcytose polymeric Ab across the epithelium, were also protected from CDI, suggesting that although mucosal anti-toxin Ab may contribute to protection, it is not required. We conclude that protection from CDI can occur by several mechanisms and that the mechanism of protection is determined by the state of immunocompetence of the host.

Novel adjuvants & delivery vehicles for vaccines development: a road ahead

The pure recombinant and synthetic antigens used in modern day vaccines are generally less immunogenic than older style live/attenuated and killed whole organism vaccines. One can improve the quality of vaccine production by incorporating immunomodulators or adjuvants with modified delivery vehicles viz. liposomes, immune stimulating complexes (ISCOMs), micro/nanospheres apart from alum, being used as gold standard. Adjuvants are used to augment the effect of a vaccine by stimulating the immune system to respond to the vaccine, more vigorously, and thus providing increased immunity to a particular disease. Adjuvants accomplish this task by mimicking specific sets of evolutionary conserved molecules which include lipopolysaccharides (LPS), components of bacterial cell wall, endocytosed nucleic acids such as dsRNA, ssDNA and unmethylated CpG dinucleotide containing DNA. This review provides information on various vaccine adjuvants and delivery vehicles being developed to date. From literature, it seems that the humoral immune responses have been observed for most adjuvants and delivery platforms while viral-vector, ISCOMs and Montanides have shown cytotoxic T-cell response in the clinical trials. MF59 and MPL® have elicited Th1 responses, and virus-like particles (VLPs), non-degradable nanoparticle and liposomes have also generated cellular immunity. Such vaccine components have also been evaluated for alternative routes of administration with clinical success reported for intranasal delivery of viral-vectors and proteosomes and oral delivery of VLP vaccines.

Carbohydrate-based Clostridium difficile vaccines

Clostridium difficile is responsible for thousands of deaths each year and a vaccine would be welcomed, especially one that would disrupt bacterial maintenance, colonization and persistence in carriers and convalescent patients. Structural explorations at the University of Guelph (ON, Canada) discovered that C. difficile may express three phosphorylated polysaccharides, named PSI, PSII and PSIII; this review captures our recent efforts to create vaccines based on these glycans, especially PSII, the common antigen that has precipitated immediate attention. The authors describe the design and immunogenicity of vaccines composed of raw polysaccharides and conjugates thereof. So far, it has been observed that anti-PSII antibodies can be raised in farm animals, mice and hamster models; humans and horses carry anti-PSII IgA and IgG antibodies from natural exposure to C. difficile, respectively; phosphate is an indispensable immunogenic epitope and vaccine-induced PSII antibodies recognize PSII on C. difficile outer surface.

Immunological evaluation of a synthetic Clostridium difficile oligosaccharide conjugate vaccine candidate and identification of a minimal epitope

Clostridium difficile is the cause of emerging nosocomial infections that result in abundant morbidity and mortality worldwide. Thus, the development of a vaccine to kill the bacteria to prevent this disease is highly desirable. Several recently identified bacterial surface glycans, such as PS-I and PS-II, are promising vaccine candidates to preclude C. difficile infection. To circumvent difficulties with the generation of natural PS-I due to its low expression levels in bacterial cultures, improved chemical synthesis protocols for the pentasaccharide repeating unit of PS-I and oligosaccharide substructures were utilized to produce large quantities of well-defined PS-I related glycans. The analysis of stool and serum samples obtained from C. difficile patients using glycan microarrays of synthetic oligosaccharide epitopes revealed humoral immune responses to the PS-I related glycan epitopes. Two different vaccine candidates were evaluated in the mouse model. A synthetic PS-I repeating unit CRM197 conjugate was immunogenic in mice and induced immunoglobulin class switching as well as affinity maturation. Microarray screening employing PS-I repeating unit substructures revealed the disaccharide Rha-(1→3)-Glc as a minimal epitope. A CRM197-Rha-(1→3)-Glc disaccharide conjugate was able to elicit antibodies recognizing the C. difficile PS-I pentasaccharide. We herein demonstrate that glycan microarrays exposing defined oligosaccharide epitopes help to determine the minimal immunogenic epitopes of complex oligosaccharide antigens. The synthetic PS-I pentasaccharide repeating unit as well as the Rha-(1→3)-Glc disaccharide are promising novel vaccine candidates against C. difficile that are currently in preclinical evaluation.

Toll-like receptor 5-dependent immunogenicity and protective efficacy of a recombinant fusion protein vaccine containing the nontoxic domains of Clostridium difficile toxins A and B and Salmonella enterica serovar typhimurium flagellin in a mouse model of Clostridium difficile disease

Clostridium difficile is a spore-forming bacillus that produces toxin-mediated enteric disease. C. difficile expresses two major virulence factors, toxin A (TcdA) and toxin B (TcdB). Human and animal studies demonstrate a clear association between humoral immunity to these toxins and protection against C. difficile infection (CDI). The receptor binding-domains (RBDs) of TcdA and TcdB are known to be immunogenic. Here, we tested the immunoadjuvant properties of Salmonella enterica serovar Typhimurium flagellin (FliC) subunit D1 as an innate immune agonist expressed as a recombinant fusion vaccine targeting the RBDs of TcdA and TcdB in mice. Intraperitoneally immunized mice developed prominent anti-TcdA and anti-TcdB immunoglobulin G in serum. The protective efficacy of the recombinant vaccines, with or without an adjuvant, was tested in a mouse model of CDI that closely represents the human disease. Following intraperitoneal immunization equivalent to two doses of toxoid A and toxoid B vaccine adjuvanted with alum and oral challenge with C. difficile VPI 10463, C57BL/6 mice were able to mount a protective immune response that prevented diarrhea and death compared to mice immunzed with alum alone. These results are significantly different from those for control mice (P < 0.001). These results provide evidence that a recombinant protein-based vaccine targeting the RBDs of the C. difficile toxins adjuvanted with S. Typhimurium flagellin can induce rapid, high-level protection in a mouse model of CDI when challenged with the homologous strain from which the vaccine antigens were derived and warrant further preclinical testing against clinically relevant C. difficile strains in the mouse and hamster models of CDI.

Development and optimization of a novel assay to measure neutralizing antibodies against Clostridium difficile toxins

Clostridium difficile produces two major virulence toxins, toxin A (TcdA) and toxin B (TcdB). Antitoxin antibodies, especially neutralizing antibodies, have been shown to be associated with a lower incidence of C. difficile infection (CDI) recurrence, and antibody levels are predictive of asymptomatic colonization. The development of an assay to detect the presence of neutralizing antibodies in animal and human sera for the evaluation of vaccine efficacy is highly desired. We have developed such an assay, which allows for the quantification of the effect of toxins on eukaryotic cells in an automated manner. We describe here the optimization of this assay to measure toxin potency as well as neutralizing antibody (NAb) activity against C. difficile toxins using a design-of-experiment (DOE) methodology. Toxin concentration and source, cell seeding density, and serum-toxin preincubation time were optimized in the assay using Vero cells. The assay was shown to be robust and to produce linear results across a range of antibody concentrations. It can be used to quantify neutralizing antibodies in sera of monkeys and hamsters immunized with C. difficile toxoid vaccines. This assay was shown to correlate strongly with traditional assays which rely on labor-intensive methods of determining neutralizing antibody titers by visual microscopic inspection of intoxicated-cell monolayers. This assay has utility for the selection and optimization of C. difficile vaccine candidates.

Transcutaneous vaccination via laser microporation

Driven by constantly increasing knowledge about skin immunology, vaccine delivery via the cutaneous route has recently gained renewed interest. Considering its richness in immunocompetent cells, targeting antigens to the skin is considered to be more effective than intramuscular or subcutaneous injections. However, circumvention of the superficial layer of the skin, the stratum corneum, represents the major challenge for cutaneous immunization. An optimal delivery method has to be effective and reliable, but also highly adaptable to specific demands, should avoid the use of hypodermic needles and the requirement of specially trained healthcare workers. The P.L.E.A.S.E.® (Precise Laser Epidermal System) device employed in this study for creation of aqueous micropores in the skin fulfills these prerequisites by combining the precision of its laser scanning technology with the flexibility to vary the number, density and the depth of the micropores in a user-friendly manner. We investigated the potential of transcutaneous immunization via laser-generated micropores for induction of specific immune responses and compared the outcomes to conventional subcutaneous injection. By targeting different layers of the skin we were able to bias polarization of T cells, which could be modulated by addition of adjuvants. The P.L.E.A.S.E.® device represents a highly effective and versatile platform for transcutaneous vaccination.

A chimeric toxin vaccine protects against primary and recurrent Clostridium difficile infection

The global emergence of Clostridium difficile infection (CDI) has contributed to the recent surge in severe antibiotic-associated diarrhea and colonic inflammation. C. difficile produces two homologous glucosylating exotoxins, TcdA and TcdB, both of which are pathogenic and require neutralization to prevent disease occurrence. However, because of their large size and complex multifunctional domain structures, it has been a challenge to produce native recombinant toxins that may serve as vaccine candidates. Here, we describe a novel chimeric toxin vaccine that retains major neutralizing epitopes from both toxins and confers complete protection against primary and recurrent CDI in mice. Using a nonpathogenic Bacillus megaterium expression system, we generated glucosyltransferase-deficient holotoxins and demonstrated their loss of toxicity. The atoxic holotoxins induced potent antitoxin neutralizing antibodies showing little cross-immunogenicity or protection between TcdA and TcdB. To facilitate simultaneous protection against both toxins, we generated an active clostridial toxin chimera by switching the receptor binding domain of TcdB with that of TcdA. The toxin chimera was fully cytotoxic and showed potent proinflammatory activities. This toxicity was essentially abolished in a glucosyltransferase-deficient toxin chimera, cTxAB. Parenteral immunization of mice or hamsters with cTxAB induced rapid and potent neutralizing antibodies against both toxins. Complete and long-lasting disease protection was conferred by cTxAB vaccinations against both laboratory and hypervirulent C. difficile strains. Finally, prophylactic cTxAB vaccination prevented spore-induced disease relapse, which constitutes one of the most significant clinical issues in CDI. Thus, the rational design of recombinant chimeric toxins provides a novel approach for protecting individuals at high risk of developing CDI.

Transcutaneous immunization: an overview of advantages, disease targets, vaccines, and delivery technologies

Skin is an immunologically active tissue composed of specialized cells and agents that capture and process antigens to confer immune protection. Transcutaneous immunization takes advantage of the skin immune network by inducing a protective immune response against topically applied antigens. This mode of vaccination presents a novel and attractive approach for needle-free immunization that is safe, noninvasive, and overcomes many of the limitations associated with needle-based administrations. In this review we will discuss the developments in the field of transcutaneous immunization in the past decade with special emphasis on disease targets and vaccine delivery technologies. We will also briefly discuss the challenges that need to be overcome to translate early laboratory successes in transcutaneous immunization into the development of effective clinical prophylactics.

Models for the study of Clostridium difficile infection

Models of Clostridium difficile infection (C. difficile) have been used extensively for Clostridium difficile (C. difficile) research. The hamster model of C. difficile infection has been most extensively employed for the study of C. difficile and this has been used in many different areas of research, including the induction of C. difficile, the testing of new treatments, population dynamics and characterization of virulence. Investigations using in vitro models for C. difficile introduced the concept of colonization resistance, evaluated the role of antibiotics in C. difficile development, explored population dynamics and have been useful in the evaluation of C. difficile treatments. Experiments using models have major advantages over clinical studies and have been indispensible in furthering C. difficile research. It is important for future study programs to carefully consider the approach to use and therefore be better placed to inform the design and interpretation of clinical studies.

Transcutaneous immunization with a Vibrio cholerae O1 Ogawa synthetic hexasaccharide conjugate following oral whole-cell cholera vaccination boosts vibriocidal responses and induces protective immunity in mice

A shortcoming of currently available oral cholera vaccines is their induction of relatively short-term protection against cholera compared to that afforded by wild-type disease. We were interested in whether transcutaneous or subcutaneous boosting using a neoglycoconjugate vaccine made from a synthetic terminal hexasaccharide of the O-specific polysaccharide of Vibrio cholerae O1 (Ogawa) coupled to bovine serum albumin as a carrier (CHO-BSA) could boost lipopolysaccharide (LPS)-specific and vibriocidal antibody responses and result in protective immunity following oral priming immunization with whole-cell cholera vaccine. We found that boosting with CHO-BSA with immunoadjuvantative cholera toxin (CT) or Escherichia coli heat-labile toxin (LT) following oral priming with attenuated V. cholerae O1 vaccine strain O395-NT resulted in significant increases in serum anti-V. cholerae LPS IgG, IgM, and IgA (P < 0.01) responses as well as in anti-Ogawa (P < 0.01) and anti-Inaba (P < 0.05) vibriocidal titers in mice. The LPS-specific IgA responses in stool were induced by transcutaneous (P < 0.01) but not subcutaneous immunization. Immune responses following use of CT or LT as an adjuvant were comparable. In a neonatal mouse challenge assay, immune serum from boosted mice was associated with 79% protective efficacy against death. Our results suggest that transcutaneous and subcutaneous boosting with a neoglycoconjugate following oral cholera vaccination may be an effective strategy to prolong protective immune responses against V. cholerae.

Adenovirus-based vaccination against Clostridium difficile toxin A allows for rapid humoral immunity and complete protection from toxin A lethal challenge in mice

Clostridium difficile associated diarrhea (CDAD) is a critical public health problem worldwide with over 300,000 cases every year in the United States alone. Clearly, a potent vaccine preventing the morbidity and mortality caused by this detrimental pathogen is urgently required. However, vaccine efforts to combat C. difficile infections have been limited both in scope as well as to efficacy, as such there is not a vaccine approved for use against C. difficile to date. In this study, we have used a highly potent Adenovirus (Ad) based platform to create a vaccine against C. difficile. The Ad-based vaccine was able to generate rapid and robust humoral as well as cellular (T-cell) immune responses in mice that correlated with provision of 100% protection from lethal challenge with C. difficile toxin A. Most relevant to the clinical utility of this vaccine formulation was our result that toxin A specific IgGs were readily detected in plasma of Ad immunized mice as early as 3 days post vaccination. In addition, we found that several major immuno-dominant T cell epitopes were identified in toxin A, suggesting that the role of the cellular arm in protection from C. difficile infections may be more significant than previously appreciated. Therefore, our studies confirm that an Adenovirus based-C. difficile vaccine could be a promising candidate for prophylactic vaccination both for use in high risk patients and in high-risk environments.

The host immune response to Clostridium difficile

Clostridium difficile is the most common cause of nosocomial bacterial diarrhoea in the Western world. Diarrhoea and colitis are caused by the actions of toxins A and B released by pathogenic strains of C. difficile. Adaptive immune responses to these toxins influence the outcomes of C. difficile infection (CDI). Symptomless carriers of toxinogenic C. difficile and those with a single episode of CDI without recurrence show more robust antitoxin immune responses than those with symptomatic and recurrent disease. Immune-based approaches to CDI therapy and prevention have been developed using active vaccination or passive immunotherapy targeting C. difficile toxins. Innate immune responses to C. difficile and its toxins are also central to the pathophysiology of CDI. An acute intestinal inflammatory response with prominent neutrophil infiltration and associated tissue injury is characteristic of CDI. Furthermore, inhibiting this acute inflammatory response can protect against the intestinal injury that results from exposure to C. difficile toxins in animal models. Studies examining host risk factors for CDI have led to validated clinical prediction tools for risk of primary and of recurrent disease. Risk factors associated with severe CDI with poor clinical outcomes have also been identified and include marked elevation of the peripheral white blood cell count and elevated creatinine. However, further work is needed in this area to guide the clinical application of new approaches to disease prevention and treatment including new antimicrobials as well as passive and active immunization.

New advances in the treatment of Clostridium difficile infection (CDI)

Clostridium difficile infections (CDI) have increased in frequency throughout the world. In addition to an increase in frequency, recent CDI epidemics have been linked to a hypervirulent C. difficile strain resulting in greater severity of disease. Although most mild to moderate cases of CDI continue to respond to metronidazole or vancomycin, refractory and recurrent cases of CDI may require alternative therapies. This review provides a brief overview of CDI and summarizes studies involving alternative antibiotics, toxin binders, probiotics, and immunological therapies that can be considered for treatment of acute and recurrent CDI in severe and refractory situations.

Transcutaneous immunization as preventative and therapeutic regimens to protect against experimental otitis media due to nontypeable Haemophilus influenzae

We have developed three nontypeable Haemophilus influenzae (NTHI) adhesin-derived immunogens that are significantly efficacious against experimental otitis media (OM) due to NTHI when delivered parenterally. We now expanded our preventative immunization strategies to include transcutaneous immunization (TCI) as a less invasive, but potentially equally efficacious, regimen to prevent OM due to NTHI. Additionally, we examined the potential of TCI as a therapeutic immunization regimen to resolve ongoing experimental OM. Preventative immunization with NTHI outer membrane protein (OMP) P5- and type IV pilus-targeted immunogens, delivered with the adjuvant LT(R192G-L211A), induced significantly earlier clearance of NTHI from the nasopharynges and middle ears of challenged chinchillas compared with receipt of immunogen or adjuvant alone. Moreover, therapeutic immunization resulted in significant resolution of established NTHI biofilms from the middle ear space of animals compared with controls. These data advocate TCI with the adhesin-directed immunogens as an efficacious regimen for prevention and resolution of experimental NTHI-induced OM.

Intravenous immunoglobulin for the treatment of Clostridium difficile infection: a review

Clostridium difficile infection (CDI) has increased sharply in incidence, mortality rate, and burden on the healthcare system over the past decade. Therefore, novel treatment modalities have been developed, including intravenous immunoglobulin (IVIG). The level of immune response to Clostridium difficile colonization is the major determinant of the magnitude and duration of clinical manifestations. This effect is mediated predominantly by serum IgG anti-toxin A antibodies. Based on this finding, anti-toxin A and B antibodies were successfully used in multiple in vitro and in vivo experimental settings to passively immunize hamsters in CDI models. In humans, IVIG was used as the source of those antibodies. Fifteen small, mostly retrospective and non-randomized reports documented IVIG's success in the treatment of protracted, recurrent, or severe CDI. Diarrhea resolution rates were higher in the former patient group, but the recurrence rates were similar. IVIG mechanism of action is neutralization of mainly toxin A through IgG anti-toxin A antibodies. Purified anti-toxin A and B antibodies were successfully used to decrease CDI recurrence rates among patients with no or one previous CDI episodes. In conclusion, the efficacy of IVIG for CDI treatment in animal models has been convincingly demonstrated. However, only few small non-randomized, mostly uncontrolled reports have been published on human subjects. A phase II trial results support the use of purified anti-toxin A and B antibodies to decrease CDI recurrence rates. Therefore, IVIG should currently only be used as adjunct therapy until results from large, randomized controlled trials are available.

The interplay between microbiome dynamics and pathogen dynamics in a murine model of Clostridium difficile Infection

Clostridium difficile infection (CDI) arises in the setting of antibiotic administration where disruption of the normal indigenous gut microbiota leads to susceptibility to C. difficile colonization and colitis. Using a murine model of CDI, we demonstrate that changes in the community structure of the indigenous gut microbiota are associated with the loss of colonization resistance against C. difficile. Several antibiotic regimens were tested in combination for the ability to overcome colonization resistance, including a five antibiotic cocktail consisting of kanamycin, gentamicin, colistin, metronidazole, and vancomycin administered in drinking water for three days, a single intraperitoneal dose of clindamycin or 10 days of cefoperazone in drinking water. Following antibiotic treatment animals were challenged with 105 colony forming units of C. difficile strain VPI 10463 via oral gavage. Animals that received the antibiotic cocktail and clindamycin prior to C. difficile challenge followed one of two clinical courses, either becoming clinically ill and moribund within 2-4 days post challenge, or remaining clinically well. Animals that became clinically ill developed histologically severe colitis. These histopathologic findings were significantly less severe in animals that remained clinically well. Analysis of 16S rRNA gene sequences retrieved from gut tissue at necropsy demonstrated that Proteobacteria dominated the gut microbiota in clinically ill animals. In contrast, the gut microbial community of clinically well animals more closely resembled untreated animals, which were dominated by members of the Firmicutes. All animals that received cefoperazone treatment prior to C. difficile challenge were clinically ill and moribund by 2-5 days post challenge in a dose dependent manner. The gut communities in these animals were dominated by C.difficile suggesting that cefoperazone treatment resulted in a greater loss in colonization resistance. Thus, the severity of colitis that arises in this system reflects the interplay between the expansion of C. difficile in the gut community and the ecologic dynamics of the indigenous microbial community as it recovers from antibiotic perturbation. We demonstrate that altering the balance of these two opposing processes alters clinical outcome and thus may lead to novel preventative and therapeutic approaches for CDI.

The ecology and pathobiology of Clostridium difficile infections: an interdisciplinary challenge

Clostridium difficile is a well recognized pathogen of humans and animals. Although C. difficile was first identified over 70 years ago, much remains unknown in regards to the primary source of human acquisition and its pathobiology. These deficits in our knowledge have been intensified by dramatic increases in both the frequency and severity of disease in humans over the last decade. The changes in C. difficile epidemiology might be due to the emergence of a hypervirulent stain of C. difficile, ageing of the population, altered risk of developing infection with newer medications, and/or increased exposure to C. difficile outside of hospitals. In recent years, there have been numerous reports documenting C. difficile contamination of various foods, and reports of similarities between strains that infect animals and strains that infect humans as well. The purposes of this review are to highlight the many challenges to diagnosing, treating, and preventing C. difficile infection in humans, and to stress that collaboration between human and veterinary researchers is needed to control this pathogen.

The potential value of Clostridium difficile vaccine: an economic computer simulation model

Efforts are currently underway to develop a vaccine against Clostridium difficile infection (CDI). We developed two decision analytic Monte Carlo computer simulation models: (1) an Initial Prevention Model depicting the decision whether to administer C. difficile vaccine to patients at-risk for CDI and (2) a Recurrence Prevention Model depicting the decision whether to administer C. difficile vaccine to prevent CDI recurrence. Our results suggest that a C. difficile vaccine could be cost-effective over a wide range of C. difficile risk, vaccine costs, and vaccine efficacies especially, when being used post-CDI treatment to prevent recurrent disease.

Intravenous immunoglobulin for the treatment of severe Clostridium difficile colitis: an observational study and review of the literature

BACKGROUND

Clostridium difficile colitis (CDC) is the most common cause of hospital-acquired diarrhea. The increase in the incidence and fatality rate of CDC over the past decade has stimulated a search for new therapies, including intravenous immunoglobulin (IVIG). We report our experience with IVIG for the treatment of 21 patients with severe CDC.

METHOD

Retrospective review of patients with severe CDC who received IVIG between July 2002 and April 2006 at a teaching hospital. The existing literature on IVIG infusion for severe CDC was also reviewed.

RESULTS

Twenty-one of 1230 patients with CDC were treated with IVIG. The mean age was 68 (range, 35-98) years, with mean hospital stay of 23 (range, 9-64) days. Conventional treatment was used for an average of 8 (range, 1-25) days before IVIG infusion. All patients had evidence of pancolitis (radiologically) or ileus (clinically). The mean Acute Physiological Assessment and Chronic Health Evaluation (APACHE II) score was 25 (range, 6-39) at day 1 of IVIG infusion. Nine patients (43%) survived their hospitalization with colitis resolution while 12 (57%) died. One patient developed pulmonary edema after IVIG infusion. Symptoms resolved after an average of 10 (range, 2-20) days for survivors. Two patients underwent urgent colectomy.

CONCLUSIONS

This is the largest case series describing IVIG use for patients with severe CDC and the one with the highest mortality rate to date. The use of IVIG in this setting does not seem to benefit all patients. Benefit appears to depend on the extent of systemic involvement. Further studies are needed before adopting IVIG as routine treatment for severe CDC.

Transcutaneous immunization with a synthetic hexasaccharide-protein conjugate induces anti-Vibrio cholerae lipopolysaccharide responses in mice

Antibodies specific for Vibrio cholerae lipopolysaccaride (LPS) are common in humans recovering from cholera, and constitute a primary component of the vibriocidal response, a serum complement-mediated bacteriocidal response correlated with protection against cholera. In order to determine whether transcutaneous immunization (TCI) with a V. cholerae neoglycoconjugate (CHO-BSA) comprised of a synthetic terminal hexasaccharide of the O-specific polysaccharide of V. cholerae O1 (Ogawa) conjugated with bovine serum albumin (BSA) could induce anti-V. cholerae LPS and vibriocidal responses, we applied CHO-BSA transcutaneously in the presence or absence of the immune adjuvant cholera toxin (CT) to mice. Transcutaneously applied neoglycoconjugate elicited prominent V. cholerae specific LPS IgG responses in the presence of CT, but not IgM or IgA responses. CT applied on the skin induced strong IgG and IgA serum responses. TCI with neoglycoconjugate did not elicit detectable vibriocidal responses, protection in a mouse challenge assay, or stool anti-V. cholerae IgA responses, irrespective of the presence or absence of CT. Our results suggest that transcutaneously applied synthetic V. cholerae neoglycoconjugate is safe and immunogenic, but predominantly induces systemic LPS responses of the IgG isotype.

Comparison of different doses of antigen for intradermal administration in pigs: the Actinobacillus pleuropneumoniae model

The intensity of antibody responses and level of protection against challenge infection induced by Actinobacillus pleuropneumoniae (APP) were compared in piglets vaccinated intramuscularly with different vaccination doses of a subunit vaccine. Secondary antibody responses to APP exotoxins induced by the intradermally administered diluted vaccines did not differ from those induced by undiluted vaccines administered either intradermally or intramuscularly. The level of protection measured by the clinical course of challenge infection to the extent of lung lesions was significantly higher in animals vaccinated with a three-time diluted vaccine in comparison with animals that were administered intramuscularly or intradermally with the most concentrated or the most diluted vaccines.

A case for immunization against nosocomial infections

Immunization is a highly effective public health measure that reduces the incidence of infectious diseases, yet there has been relatively little effort toward the development of vaccines for nosocomial infections. Many nosocomial infections originate on mucosal surfaces (e.g., respiratory or gastrointestinal mucosa). As patients who are hospitalized once are more likely to be hospitalized again, we propose a prime-boost immunization strategy, whereby a priming dose of vaccine for a nosocomial infection is administered mucosally. Upon readmission, a parenteral boost would elicit a rapid immune response locally and systemically. Such a strategy could reduce or ameliorate nosocomial infections and perhaps limit dissemination of nosocomial pathogens. Thus, a more aggressive effort to develop vaccines for nosocomial infections is warranted.

Transcutaneous immunization with heat-labile enterotoxin: development of a needle-free vaccine patch

The skin is an attractive target for vaccine delivery. Adjuvants and antigens delivered into the skin can result in potent immune responses and an unmatched safety profile. The heat-labile enterotoxin (LT) from Escherichia coli, which acts both as antigen and adjuvant, has been shown to be delivered to human skin efficiently when used in a patch, resulting in strong immune responses. Iomai scientists have capitalized on these observations to develop late-stage products based on LT. This has encouraged commercial-level product development of a delivery system that is efficient, user-friendly and designed to address important medical needs. Over the past 2 years, extensive clinical testing and optimization has allowed the patch to evolve to a late-stage product. As a strategy for approval of a revolutionary vaccine-delivery system, the singular focus on optimization of LT delivery has enabled technical progress to extend patch-vaccine product development beyond LT. The field efficacy of the LT-based travelers' diarrhea vaccine has validated this approach. The discussion of transcutaneous immunization is unique, in that any consideration of the adjuvant must also include delivery, and the significant advances in a commercial patch application system are described. In this review, we integrate these concepts, update the clinical data and look to the future.

Transcutaneous immunization by merely prolonging the duration of antigen presence on the skin of mice induces a potent antigen-specific antibody response even in the absence of an adjuvant

Transcutaneous immunization (TCI) is a promising needle-free technique for vaccination. In this method, strong adjuvants, such as the cholera toxin, are generally crucial to elicit a robust immune response. Here, we showed that prolonged antigen presence on the skin of mice during TCI could effectively enhance the immune response. Substantial antigen-specific antibodies were produced in the sera of mice even after non-adjuvanted TCI when the antigen presence was for longer than 16 h. This non-adjuvanted TCI method was applied using the tetanus toxoid, and potent tetanus toxoid-specific antibodies were successfully induced in the sera of mice; they survived a lethal tetanus toxin challenge with no clinical signs. Thus, non-adjuvanted approach might be a possible option for TCI, and this method might improve the safety and practicality of transcutaneous vaccination.