Safety, immunogenicity and dose response of VLA84, a new vaccine candidate against Clostridium difficile, in healthy volunteers

Against Clostridioides difficile Infection: An Update on Vaccine Development

Clostridioides difficile (C. difficile) is a major pathogen responsible for antibiotic-associated diarrhea, frequently observed in hospital settings. Due to the widespread use of antibiotics, the incidence and severity of C. difficile infection (CDI) are rising across the world. CDI is primarily driven by two homologous protein exotoxins, toxin A (TcdA) and toxin B (TcdB). Other putative virulence factors include binary toxin CDT, surface layer proteins, phosphorylated polysaccharides, and spore coat proteins. These C. difficile virulence factors are potential targets for vaccine development. Although several C. difficile vaccines have entered clinical trials, there is currently no approved vaccine on the market. This review outlines the intoxication mechanism during CDI, emphasizing the potential antigens that can be used for vaccine development. We aim to provide a comprehensive overview of the current status of research and development of C. difficile vaccines.

Evaluation of the Potency of the First Commercial Vaccine for Clostridioides difficile Infection in Piglets and Comparison with the Humoral Response in Rabbits

Clostridioides difficile is an anaerobic bacterium that causes disease in both animals and humans. Despite the known significance of this agent, there are no commercial vaccines available for humans, and only one immunogen is marketed for swine. However, no studies have evaluated this vaccine.

BACKGROUND/OBJECTIVES

Therefore, the aim of this study was to assess the potency of the first commercial vaccine for C. difficile infection in piglets and to compare the humoral response in rabbits and sows.

METHODS

Pregnant sows were divided into two groups: a vaccinated group (n = 12), receiving two doses before farrowing, according to the manufacturer's recommendation, and an unvaccinated control group (n = 6). Blood samples were taken from sows and also from piglets up to two days after birth. In addition, two groups of New Zealand rabbits (Oryctolagus cuniculus) received either a half-dose (G1) or a full-dose (G2) of the vaccine, with a control group receiving sterile saline (0.85%). Rabbits were vaccinated twice, 21 days apart, with blood samples collected before each dose and 14 days after the final dose. A serum neutralization assay in Vero cells was performed to evaluate the titers of neutralizing antibodies.

RESULTS

The vaccine demonstrated immunogenicity by stimulating the production of neutralizing antibodies in both rabbits and sows. Additionally, these antibodies were passively transferred to piglets through colostrum, reaching levels comparable to those found in sows. Furthermore, vaccinated rabbits developed antibody titers that do not significantly differ from those obtained in sows and piglets.

CONCLUSIONS

The tested vaccine can induce a humoral immune response against C. difficile A/B toxins in sows and these antibodies are passively transferred to neonatal piglets through colostrum. Also, the vaccination of rabbits might be a useful alternative for evaluating the potency of vaccines against C. difficile.

Safety and Immunogenicity of an Adjuvanted Clostridioides difficile Vaccine Candidate in Healthy Adults: A Randomized Placebo-Controlled Phase 1 Study

BACKGROUND

This study investigated the safety, reactogenicity, and immunogenicity in healthy subjects of a Clostridioides difficile vaccine candidate with/without adjuvant, targeting toxins A and B.

METHODS

In this first-in-human, phase 1, observer-blind study, subjects aged 18-45 years were randomized to receive F2 antigen (n = 10) or placebo (n = 10), and subjects aged 50-70 years to receive F2 antigen plus AS01 adjuvant (n = 45), F2 antigen (n = 45), or placebo (n = 30) in 2 doses 1 month apart. A subcohort (n = 40) received a third dose 15 months later. Solicited adverse events (AEs) were recorded for 7 days and unsolicited AEs for 30 days after each dose. Immunogenicity was assessed at baseline and after each dose.

RESULTS

Solicited AEs were transient and most frequent in subjects receiving F2 antigen plus AS01. No serious AEs were considered related to study vaccine. Immunogenicity was substantially higher in subjects receiving F2 antigen plus AS01 than subjects receiving F2 antigen alone. A third dose increased the immune response in subjects with baseline neutralization titers below the assay lower limit of quantitation.

CONCLUSIONS

The GSK C. difficile vaccine candidate was immunogenic, especially when given with AS01, and was well tolerated with an acceptable safety profile.

CLINICAL TRIAL REGISTRATION

NCT04026009.

Vaccines and monoclonal antibodies to prevent healthcare-associated bacterial infections

SUMMARYHealthcare-associated infections (HAIs) represent a burden for public health with a high prevalence and high death rates associated with them. Pathogens with a high potential for antimicrobial resistance, such as ESKAPE pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species) and Clostridioides difficile, are responsible for most HAIs. Despite the implementation of infection prevention and control intervention, globally, HAIs prevalence is stable and they are mainly due to endogenous pathogens. It is undeniable that complementary to infection prevention and control measures, prophylactic approaches by active or passive immunization are needed. Specific groups at-risk (elderly people, chronic condition as immunocompromised) and also healthcare workers are key targets. Medical procedures and specific interventions are known to be at risk of HAIs, in addition to hospital environmental exposure. Vaccines or monoclonal antibodies can be seen as attractive preventive approaches for HAIs. In this review, we present an overview of the vaccines and monoclonal antibodies in clinical development for prevention of the major bacterial HAIs pathogens. Based on the current state of knowledge, we look at the challenges and future perspectives to improve prevention by these means.

Immunogenicity and safety in rabbits of a Clostridioides difficile vaccine combining novel toxoids and a novel adjuvant

Clostridioides difficile infection (CDI) is a serious healthcare-associated disease, causing symptoms such as diarrhea and pseudomembranous colitis. The major virulence factors responsible for the disease symptoms are two secreted cytotoxic proteins, TcdA and TcdB. A parenteral vaccine based on formaldehyde-inactivated TcdA and TcdB supplemented with alum adjuvant, has previously been investigated in humans but resulted in an insufficient immune response. In search for an improved response, we investigated a novel toxin inactivation method and a novel, potent adjuvant. Inactivation of toxins by metal-catalyzed oxidation (MCO) was previously shown to preserve neutralizing epitopes and to annihilate reversion to toxicity. The immunogenicity and safety of TcdA and TcdB inactivated by MCO and combined with a novel carbohydrate fatty acid monosulphate ester-based (CMS) adjuvant were investigated in rabbits. Two or three intramuscular immunizations generated high serum IgG and neutralizing antibody titers against both toxins. The CMS adjuvant increased antibody responses to both toxins while an alum adjuvant control was effective only against TcdA. Systemic safety was evaluated by monitoring body weight, body temperature, and analysis of red and white blood cell counts shortly after immunization. Local safety was assessed by histopathologic examination of the injection site at the end of the study. Body weight gain was constant in all groups. Body temperature increased up to 1 ˚C one day after the first immunization but less after the second or third immunization. White blood cell counts, and percentage of neutrophils increased one day after immunization with CMS-adjuvanted vaccines, but not with alum. Histopathology of the injection sites 42 days after the last injection did not reveal any abnormal tissue reactions. From this study, we conclude that TcdA and TcdB inactivated by MCO and combined with CMS adjuvant demonstrated promising immunogenicity and safety in rabbits and could be a candidate for a vaccine against CDI.

Advances in Therapeutic Strategies for the Management of Clostridioides difficile Infection

The infection caused by Clostridioides difficile represents one of the bacterial infections with the greatest increase in incidence among nosocomial infections in recent years. C. difficile is a Gram-positive bacterium able to produce toxins and spores. In some cases, infection results in severe diarrhoea and fulminant colitis, which cause prolonged hospitalisation and can be fatal, with repercussions also in terms of health economics. C. difficile is the most common cause of antibiotic-associated diarrhoea in the healthcare setting. The problem of bacterial forms that are increasingly resistant to common antibiotic treatments is also reflected in C. difficile infection (CDI). One of the causes of CDI is intestinal dysmicrobialism induced by prolonged antibiotic therapy. Moreover, in recent years, the emergence of increasingly virulent strains resistant to antibiotic treatment has made the picture even more complex. Evidence on preventive treatments to avoid recurrence is unclear. Current guidelines indicate the following antibiotics for the treatment of CDI: metronidazole, vancomycin, and fidaxomycin. This short narrative review provides an overview of CDI, antibiotic resistance, and emerging treatments.

Multimodal vaccination targeting the receptor binding domains of Clostridioides difficile toxins A and B with an attenuated Salmonella Typhimurium vector (YS1646) protects mice from lethal challenge

Developing a vaccine against Clostridioides difficile is a key strategy to protect the elderly. Two candidate vaccines using a traditional approach of intramuscular (IM) delivery of recombinant antigens targeting C. difficile toxins A (TcdA) and B (TcdB) failed to meet their primary endpoints in large phase 3 trials. To elicit a mucosal response against C. difficile, we repurposed an attenuated strain of Salmonella Typhimurium (YS1646) to deliver the receptor binding domains (rbd) of TcdA and TcdB to the gut-associated lymphoid tissues, to elicit a mucosal response against C. difficile. In this study, YS1646 candidates with either rbdA or rbdB expression cassettes integrated into the bacterial chromosome at the attTn7 site were generated and used in a short-course multimodal vaccination strategy that combined oral delivery of the YS1646 candidate(s) on days 0, 2, and 4 and IM delivery of recombinant antigen(s) on day 0. Five weeks after vaccination, mice had high serum IgG titers and increased intestinal antigen-specific IgA titers. Multimodal vaccination increased the IgG avidity compared to the IM-only control. In the mesenteric lymph nodes, we observed increased IL-5 secretion and increased IgA+ plasma cells. Oral vaccination skewed the IgG response toward IgG2c dominance (vs IgG1 dominance in the IM-only group). Both oral alone and multimodal vaccination against TcdA protected mice from lethal C. difficile challenge (100% survival vs 30% in controls). Given the established safety profile of YS1646, we hope to move this vaccine candidate forward into a phase I clinical trial.IMPORTANCEClostridioides difficile remains a major public health threat, and new approaches are needed to develop an effective vaccine. To date, the industry has focused on intramuscular vaccination targeting the C. difficile toxins. Multiple disappointing results in phase III trials have largely confirmed that this may not be the best strategy. As C. difficile is a pathogen that remains in the intestine, we believe that targeting mucosal immune responses in the gut will be a more successful strategy. We have repurposed a highly attenuated Salmonella Typhimurium (YS1646), originally pursued as a cancer therapeutic, as a vaccine vector. Using a multimodal vaccination strategy (both recombinant protein delivered intramuscularly and YS1646 expressing antigen delivered orally), we elicited both systemic and local immune responses. Oral vaccination alone completely protected mice from lethal challenge. Given the established safety profile of YS1646, we hope to move these vaccine candidates forward into a phase I clinical trial.

Immunization Strategies Against Clostridioides difficile

Clostridioides difficile (C. difficile) infection (CDI) is an important healthcare but also a community-associated disease. CDI is considered a public health threat and an economic burden. A major problem is the high rate of recurrences. Besides classical antibiotic treatments, new therapeutic strategies are needed to prevent infection, to treat patients, and to prevent recurrences. If fecal transplantation has been recommended to treat recurrences, another key approach is to elicit immunity against C. difficile and its virulence factors. Here, after a summary concerning the virulence factors, the host immune response against C. difficile, and its role in the outcome of disease, we review the different approaches of passive immunotherapies and vaccines developed against CDI. Passive immunization strategies are designed in function of the target antigen, the antibody-based product, and its administration route. Similarly, for active immunization strategies, vaccine antigens can target toxins or surface proteins, and immunization can be performed by parenteral or mucosal routes. For passive immunization and vaccination as well, we first present immunization assays performed in animal models and second in humans and associated clinical trials. The different studies are presented according to the mode of administration either parenteral or mucosal and the target antigens and either toxins or colonization factors.

Clostridioides difficile infections; new treatments and future perspectives

PURPOSE OF REVIEW

As a significant cause of global morbidity and mortality, Clostridioides difficile infections (CDIs) are listed by the Centres for Disease Control and prevention as one of the top 5 urgent threats in the USA. CDI occurs from gut microbiome dysbiosis, typically through antibiotic-mediated disruption; however, antibiotics are the treatment of choice, which can result in recurrent infections. Here, we highlight new treatments available and provide a perspective on different classes of future treatments.

RECENT FINDINGS

Due to the reduced risk of disease recurrence, the microbiome-sparing antibiotic Fidaxomicin has been recommended as the first-line treatment for C. difficile infection. Based on the success of faecal microbiota transplantations (FMT) in treating CDI recurrence, defined microbiome biotherapeutics offer a safer and more tightly controlled alterative as an adjunct to antibiotic therapy. Given the association between antibiotic-mediated dysbiosis of the intestinal microbiota and the recurrence of CDI, future prospective therapies aim to reduce the dependence on antibiotics for the treatment of CDI.

SUMMARY

With current first-in-line antibiotic therapy options associated with high levels of recurrent CDI, the availability of new generation targeted therapeutics can really impact treatment success. There are still unknowns about the long-term implications of these new CDI therapeutics, but efforts to expand the CDI treatment toolbox can offer multiple solutions for clinicians to treat this multifaceted infectious disease to reduce patient suffering.

A phase 3 study evaluating the lot consistency, immunogenicity, safety, and tolerability of a Clostridioides difficile vaccine in healthy adults 65 to 85 years of age

BACKGROUND

A toxoid-based Clostridioides difficile vaccine is currently in development. Here, we report lot-to-lot consistency, immunogenicity, safety, and tolerability of 3 C difficile vaccine doses in healthy older adults.

METHODS

This phase 3, placebo-controlled study randomized (1:1:1:1) healthy adults 65 to 85 years of age to 1 of 3 C difficile vaccine lots or placebo. Participants received C difficile vaccine (200 μg total toxoid) or placebo (Months 0, 1, 6). The primary immunogenicity objective was lot-to-lot consistency (2-sided 95 % CIs within 0.5 and 2 for comparisons of geometric mean concentration [GMC] ratios) for toxins A- and B-specific neutralizing antibody levels 1 month after Dose 3. Safety outcomes included local reactions and systemic events ≤7 days after vaccination, adverse events (AEs), and serious AEs (SAEs).

RESULTS

Of 1317 enrolled participants, 1218 completed the study. C difficile vaccine immunogenicity was consistent across lots, with neutralizing antibody responses 1 month after Dose 3 for both toxin A (GMC [95 % CI]: lot 1, 878.8 [786.3, 982.2]; lot 2, 873.0 [779.2, 978.1]; lot 3, 872.9 [782.6, 973.5]) and toxin B (lot 1, 5823.9 [5041.0, 6728.4]; lot 2, 5462.8 [4733.4, 6304.7]; lot 3, 5426.0 [4724.4, 6231.8]). Two-sided 95 % CIs for GMC ratios were within 0.5 and 2 for toxins A and B, indicating lot-to-lot consistency was achieved. C difficile vaccine was well tolerated, with similar rates of local reactions and systemic events among vaccine lots. AE and SAE rates were similar across C difficile vaccine (36.5 % and 4.5 %, respectively) and placebo (35.3 % and 6 %).

CONCLUSIONS

Three doses (Months 0,1,6) of toxoid-based C difficile vaccine induced robust neutralizing antibody responses and were well tolerated in healthy participants 65 to 85 years of age. Lot-to-lot consistency was excellent, indicating the manufacturing process for this C difficile vaccine formulation was well controlled.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov identifier: NCT03579459.

Host Immune Responses to Clostridioides difficile Infection and Potential Novel Therapeutic Approaches

Clostridioides difficile infection (CDI) is a leading nosocomial infection, posing a substantial public health challenge within the United States and globally. CDI typically occurs in hospitalized elderly patients who have been administered antibiotics; however, there has been a rise in the occurrence of CDI in the community among young adults who have not been exposed to antibiotics. C. difficile releases toxins, which damage large intestinal epithelium, leading to toxic megacolon, sepsis, and even death. Unfortunately, existing antibiotic therapies do not always prevent these consequences, with up to one-third of treated patients experiencing a recurrence of the infection. Host factors play a crucial role in the pathogenesis of CDI, and accumulating evidence shows that modulation of host immune responses may potentially alter the disease outcome. In this review, we provide an overview of our current knowledge regarding the role of innate and adaptive immune responses on CDI outcomes. Moreover, we present a summary of non-antibiotic microbiome-based therapies that can effectively influence host immune responses, along with immunization strategies that are intended to tackle both the treatment and prevention of CDI.

Clostridioides difficile infection in the allogeneic hematopoietic cell transplant recipient

Clostridioides difficile (CD) is one of the most important causes of diarrhea in hospitalized patients, in particular those who undergo an allogeneic hematopoietic cell transplant (allo-HCT) and who are more at risk of developing a CD infection (CDI) due to frequent hospitalizations, iatrogenic immunosuppression, and prolonged antibiotic cycles. CDI may represent a severe condition in allo-HCT patients, increasing the length of hospitalization, influencing the intestinal microbiome with a bidirectional association with graft-versus-host disease, and leading to unfavorable outcomes, including death. The diagnosis of CDI requires the exclusion of other probable causes of diarrhea in HCT patients and is based on highly sensitive and highly specific tests to distinguish colonization from infection. In adult patients, fidaxomicin is recommended as first-line, with oral vancomycin as an alternative agent. Bezlotoxumab may be used to reduce the risk of recurrence. In pediatric patients, vancomycin and metronidazole are still suggested as first-line therapy, but fidaxomicin will probably become standard in pediatrics in the near future. Because of insufficient safety data, fecal microbiota transplantation is not routinely recommended in HCT in spite of promising results for the management of recurrences in other populations.

Recurrent Clostridioides difficile Infection: Current Clinical Management and Microbiome-Based Therapies

Clostridioides difficile is one of the most important causes of healthcare-associated diarrhea. The high incidence and recurrence rates of C. difficile infection, as well as its associated morbidity and mortality, are great concerns. The most common complication of C. difficile infection is recurrence, with rates of 20-30% after a primary infection and 60% after three or more episodes. Medical management of recurrent C. difficile infection involves a choice of therapy that is different from the antibiotic used in the primary episode. Patients with recurrent C. difficile infection also benefit from fecal microbiota transplantation or standardized microbiome restoration therapies (approved or experimental) to restore eubiosis. In contrast to antibiotics, microbiome restoration therapies restore a normal gut flora and eliminate C. difficile colonization and infection. Fecal microbiota transplantation in recurrent C. difficile infection has demonstrated higher success rates than vancomycin, fidaxomicin, or placebo. Fecal microbiota transplantation has traditionally been considered safe, with the most common adverse reactions being abdominal discomfort, and diarrhea, and rare serious adverse events. Significant heterogeneity and a lack of standardization regarding the process of preparation, and administration of fecal microbiota transplantation remain a major pitfall. Standardized microbiome-based therapies provide a promising alternative. In the ECOSPOR III trial of SER-109, an oral formulation of bacterial spores, a significant reduction in the recurrence rate (12%) was observed compared with placebo (40%). In the phase III PUNCH CD3 trial, RBX2660 also demonstrated high efficacy rates of 70.6% versus 57.5%. Both these agents are now US Food and Drug Administration approved for recurrent C. difficile infection. Other standardized microbiome-based therapies currently in the pipeline are VE303, RBX7455, and MET-2. Antibiotic neutralization strategies, vaccines, passive monoclonal antibodies, and drug repurposing are other therapeutic strategies being explored to treat C. difficile infection.

The Promising Potential of Reverse Vaccinology-Based Next-Generation Vaccine Development over Conventional Vaccines against Antibiotic-Resistant Bacteria

The clinical use of antibiotics has led to the emergence of multidrug-resistant (MDR) bacteria, leading to the current antibiotic resistance crisis. To address this issue, next-generation vaccines are being developed to prevent antimicrobial resistance caused by MDR bacteria. Traditional vaccine platforms, such as inactivated vaccines (IVs) and live attenuated vaccines (LAVs), were effective in preventing bacterial infections. However, they have shown reduced efficacy against emerging antibiotic-resistant bacteria, including MDR M. tuberculosis. Additionally, the large-scale production of LAVs and IVs requires the growth of live pathogenic microorganisms. A more promising approach for the accelerated development of vaccines against antibiotic-resistant bacteria involves the use of in silico immunoinformatics techniques and reverse vaccinology. The bioinformatics approach can identify highly conserved antigenic targets capable of providing broader protection against emerging drug-resistant bacteria. Multi-epitope vaccines, such as recombinant protein-, DNA-, or mRNA-based vaccines, which incorporate several antigenic targets, offer the potential for accelerated development timelines. This review evaluates the potential of next-generation vaccine development based on the reverse vaccinology approach and highlights the development of safe and immunogenic vaccines through relevant examples from successful preclinical and clinical studies.

Host Immunity and Immunization Strategies for Clostridioides difficile Infection

Clostridioides difficile infection (CDI) represents a significant challenge to public health. C. difficile-associated mortality and morbidity have led the U.S. CDC to designate it as an urgent threat. Moreover, recurrence or relapses can occur in up to a third of CDI patients, due in part to antibiotics being the primary treatment for CDI and the major cause of the disease. In this review, we summarize the current knowledge of innate immune responses, adaptive immune responses, and the link between innate and adaptive immune responses of the host against CDI. The other major determinants of CDI, such as C. difficile toxins, the host microbiota, and related treatments, are also described. Finally, we discuss the known therapeutic approaches and the current status of immunization strategies for CDI, which might help to bridge the knowledge gap in the generation of therapy against CDI.

Microbiome-Related and Infection Control Approaches to Primary and Secondary Prevention of Clostridioides difficile Infections

Clostridioides difficile infections (CDIs) have decreased in the past years, but since 2021, some hospitals have reported an increase in CDI rates. CDI remains a global concern and has been identified as an urgent threat to healthcare. Although multiple treatment options are available, prevention strategies are more limited. As CDI is an opportunistic infection that arises after the normally protective microbiome has been disrupted, preventive measures aimed at restoring the microbiome have been tested. Our aim is to update the present knowledge on these various preventive strategies published in the past five years (2018-2023) to guide clinicians and healthcare systems on how to best prevent CDI. A literature search was conducted using databases (PubMed, Google Scholar, and clinicaltrials.gov) for phase 2-3 clinical trials for the primary or secondary prevention of CDI and microbiome and probiotics. As the main factor for Clostridium difficile infections is the disruption of the normally protective intestinal microbiome, strategies aimed at restoring the microbiome seem most rational. Some strains of probiotics, the use of fecal microbial therapy, and live biotherapeutic products offer promise to fill this niche; although, more large randomized controlled trials are needed that document the shifts in the microbiome population.

Mucosal Vaccination Strategies against Clostridioides difficile Infection

Clostridioides difficile infection (CDI) presents a major public health threat by causing frequently recurrent, life-threatening cases of diarrhea and intestinal inflammation. The ability of C. difficile to express antibiotic resistance and to form long-lasting spores makes the pathogen particularly challenging to eradicate from healthcare settings, raising the need for preventative measures to curb the spread of CDI. Since C. difficile utilizes the fecal-oral route of transmission, a mucosal vaccine could be a particularly promising strategy by generating strong IgA and IgG responses that prevent colonization and disease. This mini-review summarizes the progress toward mucosal vaccines against C. difficile toxins, cell-surface components, and spore proteins. By assessing the strengths and weaknesses of particular antigens, as well as methods for delivering these antigens to mucosal sites, we hope to guide future research toward an effective mucosal vaccine against CDI.

Neutralizing epitopes on Clostridioides difficile toxin A revealed by the structures of two camelid VHH antibodies

Toxin A (TcdA) and toxin B (TcdB) are two key virulence factors secreted by Clostridioides difficile, which is listed as an urgent threat by the CDC. These two large homologous exotoxins are mainly responsible for diseases associated with C. difficile infection (CDI) with symptoms ranging from diarrhea to life threatening pseudomembranous colitis. Single-domain camelid antibodies (VHHs) AH3 and AA6 are two potent antitoxins against TcdA, which when combined with two TcdB-targeting VHHs showed effective protection against both primary and recurrent CDI in animal models. Here, we report the co-crystal structures of AH3 and AA6 when they form complexes with the glucosyltransferase domain (GTD) and a fragment of the delivery and receptor-binding domain (DRBD) of TcdA, respectively. Based on these structures, we find that AH3 binding enhances the overall stability of the GTD and interferes with its unfolding at acidic pH, and AA6 may inhibit the pH-dependent conformational changes in the DRBD that is necessary for pore formation of TcdA. These studies reveal two functionally critical epitopes on TcdA and shed new insights into neutralizing mechanisms and potential development of epitope-focused vaccines against TcdA.

Application of recombinant antibodies for treatment of Clostridioides difficile infection: Current status and future perspective

Clostridioides difficile (C. difficile), known as the major cause of antibiotic-associated diarrhea, is regarded as one of the most common healthcare-associated bacterial infections worldwide. Due to the emergence of hypervirulent strains, development of new therapeutic methods for C. difficile infection (CDI) has become crucially important. In this context, antibodies have been introduced as valuable tools in the research and clinical environments, as far as the effectiveness of antibody therapy for CDI was reported in several clinical investigations. Hence, production of high-performance antibodies for treatment of CDI would be precious. Traditional approaches of antibody generation are based on hybridoma technology. Today, application of in vitro technologies for generating recombinant antibodies, like phage display, is considered as an appropriate alternative to hybridoma technology. These techniques can circumvent the limitations of the immune system and they can be exploited for production of antibodies against different types of biomolecules in particular active toxins. Additionally, DNA encoding antibodies is directly accessible in in vitro technologies, which enables the application of antibody engineering in order to increase their sensitivity and specificity. Here, we review the application of antibodies for CDI treatment with an emphasis on recombinant fragment antibodies. Also, this review highlights the current and future prospects of the aforementioned approaches for antibody-mediated therapy of CDI.

Vaccines for healthcare associated infections without vaccine prevention to date

In spite of the widespread implementation of preventive strategies, the prevalence of healthcare-associated infections (HAIs) remains high. The prevalence of multidrug resistant organisms is high in HAIs. In 2019, the World Health Organization retained antimicrobial resistance as one of the ten issues for global health. The development of vaccines may contribute to the fight against antimicrobial resistance to reduce the burden of HAIs. Staphylococcus aureus, Gram negative bacteria and Clostridium difficile are the most frequent pathogens reported in HAIs. Consequently, the development of vaccines against these pathogens is crucial. At this stage, the goal of obtaining effective vaccines against S.aureus and Gram negative bacteria has not yet been achieved. However, we can expect in the near future availability of a vaccine against C. difficile. In addition, identifying populations who may benefit from these vaccines is complex, as at-risk patients are not great responders to vaccines, or as vaccination may occur too late, when they are already confronted to the risk. Vaccinating healthcare workers (HCWs) against these pathogens may have an impact only if HCWs play a role in the transmission and in the pathogens acquisition in patients, if the vaccine is effective to reduce pathogens carriage and if vaccine coverage is sufficient to protect patients. Acceptance of these potential vaccines should be evaluated and addressed in patients and in HCWs.

Aluminium adjuvants versus placebo or no intervention in vaccine randomised clinical trials: a systematic review with meta-analysis and Trial Sequential Analysis

OBJECTIVES

To assess the benefits and harms of aluminium adjuvants versus placebo or no intervention in randomised clinical trials in relation to human vaccine development.

DESIGN

Systematic review with meta-analysis and trial sequential analysis assessing the certainty of evidence with Grading of Recommendations Assessment, Development and Evaluation (GRADE).

DATA SOURCES

We searched CENTRAL, MEDLINE, Embase, LILACS, BIOSIS, Science Citation Index Expanded and Conference Proceedings Citation Index-Science until 29 June 2021, and Chinese databases until September 2021.

ELIGIBILITY CRITERIA

Randomised clinical trials irrespective of type, status and language of publication, with trial participants of any sex, age, ethnicity, diagnosis, comorbidity and country of residence.

DATA EXTRACTION AND SYNTHESIS

Two independent reviewers extracted data and assessed risk of bias with Cochrane's RoB tool 1. Dichotomous data were analysed as risk ratios (RRs) and continuous data as mean differences. We explored both fixed-effect and random-effects models, with 95% CI. Heterogeneity was quantified with I2 statistic. We GRADE assessed the certainty of the evidence.

RESULTS

We included 102 randomised clinical trials (26 457 participants). Aluminium adjuvants versus placebo or no intervention may have no effect on serious adverse events (RR 1.18, 95% CI 0.97 to 1.43; very low certainty) and on all-cause mortality (RR 1.02, 95% CI 0.74 to 1.41; very low certainty). No trial reported on quality of life. Aluminium adjuvants versus placebo or no intervention may increase adverse events (RR 1.13, 95% CI 1.07 to 1.20; very low certainty). We found no or little evidence of a difference between aluminium adjuvants versus placebo or no intervention when assessing serology with geometric mean titres or concentrations or participants' seroprotection.

CONCLUSIONS

Based on evidence at very low certainty, we were unable to identify benefits of aluminium adjuvants, which may be associated with adverse events considered non-serious.

Immunoinformatics Approach Toward the Introduction of a Novel Multi-Epitope Vaccine Against Clostridium difficile

Clostridium difficile (C.difficile) is an exclusively anaerobic, spore-forming, and Gram-positive pathogen that is the most common cause of nosocomial diarrhea and is becoming increasingly prevalent in the community. Because C. difficile is strictly anaerobic, spores that can survive for months in the external environment contribute to the persistence and diffusion of C. difficile within the healthcare environment and community. Antimicrobial therapy disrupts the natural intestinal flora, allowing spores to develop into propagules that colonize the colon and produce toxins, thus leading to antibiotic-associated diarrhea and pseudomembranous enteritis. However, there is no licensed vaccine to prevent Clostridium difficile infection (CDI). In this study, a multi-epitope vaccine was designed using modern computer methods. Two target proteins, CdeC, affecting spore germination, and fliD, affecting propagule colonization, were chosen to construct the vaccine so that it could simultaneously induce the immune response against two different forms (spore and propagule) of C. difficile. We obtained the protein sequences from the National Center for Biotechnology Information (NCBI) database. After the layers of filtration, 5 cytotoxic T-cell lymphocyte (CTL) epitopes, 5 helper T lymphocyte (HTL) epitopes, and 7 B-cell linear epitopes were finally selected for vaccine construction. Then, to enhance the immunogenicity of the designed vaccine, an adjuvant was added to construct the vaccine. The Prabi and RaptorX servers were used to predict the vaccine's two- and three-dimensional (3D) structures, respectively. Additionally, we refined and validated the structures of the vaccine construct. Molecular docking and molecular dynamics (MD) simulation were performed to check the interaction model of the vaccine-Toll-like receptor (TLR) complexes, vaccine-major histocompatibility complex (MHC) complexes, and vaccine-B-cell receptor (BCR) complex. Furthermore, immune stimulation, population coverage, and in silico molecular cloning were also conducted. The foregoing findings suggest that the final formulated vaccine is promising against the pathogen, but more researchers are needed to verify it.

Antigen-Specific vs. Neutralizing Antibodies Against Conditioned Media of Patients With Clostridioides difficile Infection: A Prospective Exploratory Study

The immunological response against Clostridioides difficile (C. difficile) is crucial for an improved understanding of disease mechanisms and the development of novel therapeutic strategies. From April 2014 to February 2015, adult patients with C. difficile infection (CDI) were recruited, and the clinical course and treatment response were carefully monitored. On day 1, 3, and 6 after diagnosis, patient plasma samples were screened for anti-GDH (glutamate dehydrogenase), anti-TcdA, anti-TcdB, and anti-CWP84 (cell-wall protein 84) antibodies by ELISA. Additionally, neutralization assays of toxins from conditioned media of clinical isolates (RT010, RT014, and RT027) were performed. Most patients with CDI (n = 46) had antibodies against GDH (85%) and CWP84 (61%), but only few had antibodies against TcdA (11%) and TcdB (28%). We found patients with neutralizing antibodies against C. difficile toxins (conditioned media) produced by RT027 (26%). A subgroup of these samples could neutralize both toxins from RT027 and RT014 [11%, (5/46)]; however, no single sample neutralized only RT014. Overall, neutralizing antibody titers were low (≤1:16). In a one week follow-up of acute infection, we never observed an early booster effect with seroconversion or antibody increases, irrespective of disease severity. No correlation was found between the presence of antigen-specific (ELISA) or neutralizing antibodies and the clinical course of disease. Anti-TcdB but not anti-TcdA antibodies correlated with the occurrence of neutralizing antibodies. In conclusion, natural antibody titers against C. difficile toxins were absent or low and were not associated with disease severity. The correlation between the anti-TcdB with toxin neutralization confirms the importance of TcdB for virulence of CDI. Alternative sensitization strategies, e.g., through vaccine development, are required to overcome the regular low-titer antibody production following natural intestinal C. difficile exposure.

Subtractive genomic approach toward introduction of novel immunogenic targets against Clostridioides difficile: Thinking out of the box

Clostridioides difficile is one of the major causatives of nosocomial infections worldwide. Antibiotic-associated diarrhea, pseudomembranous colitis, and toxic megacolon are the most common forms of C. difficile infection (CDI). Considering the high antibiotic resistance of C. difficile isolates and the low efficacy of immunization with toxin-related vaccines, we suggested that surface-exposed and secreted proteins could be considered as potential immunogenic targets against CDI. Various immuninformatics databases were used to predict antigenicity, allergenicity, B-cell epitopes, MHC-II binding sites, conserved domains, prevalence and conservation of proteins among the most common sequence types, molecular docking, and immunosimulation of immunogenic targets. Finally, 16 proteins belonging to three functional groups were identified, including proteins involved in the cell wall and peptidoglycan layer (nine proteins), flagellar assembly (five proteins), spore germination (one protein), and a protein with unknown function. Molecular docking results showed that among all the mentioned proteins, WP_009892971.1 (Acd) and WP_009890599.1 (a C40 family peptidase) had the strongest interactions with human Toll-like receptor 2 (TLR-2) and TLR-4. This study proposes a combination of C. difficile toxoid (Tcd) and surface-exposed proteins such as Acd as a promising vaccine formulation for protection against circulating clinical strains of C. difficile.

Frontiers in antibiotic alternatives for Clostridioides difficile infection

Clostridioides difficile (C. difficile) is a gram-positive, anaerobic spore-forming bacterium and a major cause of antibiotic-associated diarrhea. Humans are naturally resistant to C. difficile infection (CDI) owing to the protection provided by healthy gut microbiota. When the gut microbiota is disturbed, C. difficile can colonize, produce toxins, and manifest clinical symptoms, ranging from asymptomatic diarrhea and colitis to death. Despite the steady-if not rising-prevalence of CDI, it will certainly become more problematic in a world of antibiotic overuse and the post-antibiotic era. C. difficile is naturally resistant to most of the currently used antibiotics as it uses multiple resistance mechanisms. Therefore, current CDI treatment regimens are extremely limited to only a few antibiotics, which include vancomycin, fidaxomicin, and metronidazole. Therefore, one of the main challenges experienced by the scientific community is the development of alternative approaches to control and treat CDI. In this Frontier article, we collectively summarize recent advances in alternative treatment approaches for CDI. Over the past few years, several studies have reported on natural product-derived compounds, drug repurposing, high-throughput library screening, phage therapy, and fecal microbiota transplantation. We also include an update on vaccine development, pre- and pro-biotics for CDI, and toxin antidote approaches. These measures tackle CDI at every stage of disease pathology via multiple mechanisms. We also discuss the gaps and concerns in these developments. The next epidemic of CDI is not a matter of if but a matter of when. Therefore, being well-equipped with a collection of alternative therapeutics is necessary and should be prioritized.

Incidence and predictive biomarkers of Clostridioides difficile infection in hospitalized patients receiving broad-spectrum antibiotics

Trial enrichment using gut microbiota derived biomarkers by high-risk individuals can improve the feasibility of randomized controlled trials for prevention of Clostridioides difficile infection (CDI). Here, we report in a prospective observational cohort study the incidence of CDI and assess potential clinical characteristics and biomarkers to predict CDI in 1,007 patients ≥ 50 years receiving newly initiated antibiotic treatment with penicillins plus a beta-lactamase inhibitor, 3rd/4th generation cephalosporins, carbapenems, fluoroquinolones or clindamycin from 34 European hospitals. The estimated 90-day cumulative incidences of a first CDI episode is 1.9% (95% CI 1.1-3.0). Carbapenem treatment (Hazard Ratio (95% CI): 5.3 (1.7-16.6)), toxigenic C. difficile rectal carriage (10.3 (3.2-33.1)), high intestinal abundance of Enterococcus spp. relative to Ruminococcus spp. (5.4 (2.1-18.7)), and low Shannon alpha diversity index as determined by 16 S rRNA gene profiling (9.7 (3.2-29.7)), but not normalized urinary 3-indoxyl sulfate levels, predicts an increased CDI risk.

Efficient production of recombinant secretory IgA against Clostridium difficile toxins in CHO-K1 cells

Despite the essential role secretory IgAs play in the defense against pathogenic invasion and the proposed value of recombinant secretory IgAs as novel therapeutics, currently there are no IgA-based therapies in clinics. Secretory IgAs are complex molecules and the major bottleneck limiting their therapeutic potential is a reliable recombinant production system. In this report, we addressed this issue and established a fast and robust production method for secretory IgAs in CHO-K1 cells using BAC-based expression vectors. As a proof of principle, we produced IgAs against Clostridium difficile toxins TcdA and TcdB. Recombinant secretory IgAs produced using our expression system showed comparable titers to IgGs, widely used as therapeutic biologicals. Importantly, secretory IgAs produced using our method were functional and could efficiently neutralize Clostridium difficile toxins TcdA and TcdB. These results show that recombinant secretory IgAs can be efficiently produced, thus opening the possibility to use them as therapeutic agents in clinics.

AAV-mediated delivery of actoxumab and bezlotoxumab results in serum and mucosal antibody concentrations that provide protection from C. difficile toxin challenge

Clostridium difficile is the leading cause of antibiotic-associated nosocomial diarrhea in the developed world. When the host-associated colon microbiome is disrupted by the ingestion of antibiotics, C. difficile spores can germinate, resulting in infection. C. difficile secretes enterotoxin A (TcdA) and cytotoxin B (TcdB) that are responsible for disease pathology. Treatment options are limited as the bacterium demonstrates resistance to many antibiotics, and even with antibacterial therapies, recurrences of C. difficile are common. Actotoxumab and bezlotoxumab are human monoclonal antibodies that bind and neutralize TcdA and TcdB, respectively. In 2016, the US food and drug administration (FDA) approved bezlotoxumab for use in the prevention of C. difficile infection recurrence. To ensure the long-term expression of antibodies, gene therapy can be used. Here, adeno-associated virus (AAV)6.2FF, a novel triple mutant of AAV6, was engineered to express either actotoxumab or bezlotoxumab in mice and hamsters. Both antibodies expressed at greater than 90 μg/mL in the serum and were detected at mucosal surfaces in both models. Hundred percent of mice given AAV6.2FF-actoxumab survived a lethal dose of TcdA. This proof of concept study demonstrates that AAV-mediated expression of C. difficile toxin antibodies is a viable approach for the prevention of recurrent C. difficile infections.

Diagnostic and therapy of severe Clostridioides difficile infections in the ICU

PURPOSE OF REVIEW

The purpose of the review is to provide all the recent data focusing on the diagnostic and treatment of Clostridioides difficile infection in patients admitted in the ICU.

RECENT FINDINGS

In the ICU, diagnosis remains complicated with a large number of alternative diagnosis. The treatment classically relies on vancomycin but fidaxomicin and fecal microbiota transplantation are now potential solutions in selected indications.

SUMMARY

Data on ICU-related CDI remain limited and conflicting. To date, there is no unique and simple way to obtain a diagnosis for CDI, the combination of clinical signs and a two-step testing algorithm remains the recommended gold-standard. Two molecules can be proposed for first line treatment: vancomycin and fidaxomicin. Although metronidazole may still be discussed as a treatment option for mild CDI in low-risk patients, its use for ICU-patients does not seem reasonable. Several reports suggest that fecal microbiota transplantation could be discussed, as it is well tolerated and associated with a high rate of clinical cure. CDI is a dynamic and active area of research with new diagnostic techniques, molecules, and management concepts likely changing our approach to this old disease in the near future.

Enhanced Humoral Immune Responses against Toxin A and B of Clostridium difficile is Associated with a Milder Disease Manifestation

The role of the humoral immune response to Clostridium difficile in modulating the severity of C. difficile infection (CDI) is unclear. We compared the levels of serum immunoglobulin G (IgG) and immunoglobulin A (IgA) against toxin A (TcdA) and toxin B (TcdB) of C. difficile between CDI and control patients and according to disease severity. The levels of IgG and IgA antibodies against TcdA and TcdB were measured in sera from patients with CDI (n = 50; 19 had severe CDI) and control patients (n = 52), using ELISA. Patients with CDI had higher levels of IgG antibodies against TcdA and TcdB than controls (p = 0.001 and p = 0.04, respectively). Higher IgG levels against TcdA and TcdB were found in patients with mild vs. severe CDI 7-14 days after the diagnosis (p = 0.004 and 0.036, respectively). A factor analysis included both IgA and IgG levels against both toxins into one composite variable, which was of higher values in patients with mild vs. severe CDI (p = 0.026). In conclusion, the systemic humoral immune responses against TcdA and TcdB might modulate the severity of CDI. These preliminary findings provide a basis for future large-scale studies and support the development and evaluation of active and passive immunotherapies for CDI management.

Prevention and treatment of recurrent Clostridioides difficile infection

PURPOSE OF REVIEW

Clostridioides difficile infection (CDI) is a significant burden on the health system, especially due to high recurrence rates. Since the beginning of the CDI epidemic in early 2000s, many strategies for combatting recurrence have been explored, with moderate success so far. This review will focus on the most recent developments in recurrent CDI prevention and treatment.

RECENT FINDINGS

There are two main mechanisms of CDI recurrence: alteration in microbiome and poor antibody response. Development of new antibiotics aims to minimize damage to the microbiome. Fecal transplant or other microbiome replacement therapies seek to replenish the missing elements in the microbiome. Fecal microbiota transplant is the most effective treatment for prevention of CDI recurrenceso far, but is difficult to standardize and regulate, leading to efforts to develop microbiome-derived therapeutics. A deficiency in developing antibodies to C. difficile toxins is another mechanism of recurrence. Active immunization using toxoid vaccines or passive immunization using mAbs address this aspect.

SUMMARY

There are promising new treatments for recurrent CDI in development. Fecal microbiota transplant remains the most effective therapy for multiply recurrent CDI. New antibiotics, microbiome-derived therapeutics, and immunologic therapies are in development.

Ribotype Classification of Clostridioides difficile Isolates Is Not Predictive of the Amino Acid Sequence Diversity of the Toxin Virulence Factors TcdA and TcdB

Clostridioides (Clostridium) difficile is the most commonly recognized cause of infectious diarrhea in healthcare settings. Currently there is no vaccine to prevent initial or recurrent C. difficile infection (CDI). Two large clostridial toxins, TcdA and TcdB, are the primary virulence factors for CDI. Immunological approaches to prevent CDI include antibody-mediated neutralization of the cytotoxicity of these toxins. An understanding of the sequence diversity of the two toxins expressed by disease causing isolates is critical for the interpretation of the immune response to the toxins. In this study, we determined the whole genome sequence (WGS) of 478 C. difficile isolates collected in 12 countries between 2004 and 2018 to probe toxin variant diversity. A total of 44 unique TcdA variants and 37 unique TcdB variants were identified. The amino acid sequence conservation among the TcdA variants (≥98%) is considerably greater than among the TcdB variants (as low as 86.1%), suggesting that different selection pressures may have contributed to the evolution of the two toxins. Phylogenomic analysis of the WGS data demonstrate that isolates grouped together based on ribotype or MLST code for multiple different toxin variants. These findings illustrate the importance of determining not only the ribotype but also the toxin sequence when evaluating strain coverage using vaccine strategies that target these virulence factors. We recommend that toxin variant type and sequence type (ST), be used together with ribotype data to provide a more comprehensive strain classification scheme for C. difficile surveillance during vaccine development objectives.

Recommendations for the diagnosis and treatment of Clostridioides difficile infection: An official clinical practice guideline of the Spanish Society of Chemotherapy (SEQ), Spanish Society of Internal Medicine (SEMI) and the working group of Postoperative Infection of the Spanish Society of Anesthesia and Reanimation (SEDAR)

This document gathers the opinion of a multidisciplinary forum of experts on different aspects of the diagnosis and treatment of Clostridioides difficile infection (CDI) in Spain. It has been structured around a series of questions that the attendees considered relevant and in which a consensus opinion was reached. The main messages were as follows: CDI should be suspected in patients older than 2 years of age in the presence of diarrhea, paralytic ileus and unexplained leukocytosis, even in the absence of classical risk factors. With a few exceptions, a single stool sample is sufficient for diagnosis, which can be sent to the laboratory with or without transportation media for enteropathogenic bacteria. In the absence of diarrhoea, rectal swabs may be valid. The microbiology laboratory should include C. difficile among the pathogens routinely searched in patients with diarrhoea. Laboratory tests in different order and sequence schemes include GDH detection, presence of toxins, molecular tests and toxigenic culture. Immediate determination of sensitivity to drugs such as vancomycin, metronidazole or fidaxomycin is not required. The evolution of toxin persistence is not a suitable test for follow up. Laboratory diagnosis of CDI should be rapid and results reported and interpreted to clinicians immediately. In addition to the basic support of all diarrheic episodes, CDI treatment requires the suppression of antiperistaltic agents, proton pump inhibitors and antibiotics, where possible. Oral vancomycin and fidaxomycin are the antibacterials of choice in treatment, intravenous metronidazole being restricted for patients in whom the presence of the above drugs in the intestinal lumen cannot be assured. Fecal material transplantation is the treatment of choice for patients with multiple recurrences but uncertainties persist regarding its standardization and safety. Bezlotoxumab is a monoclonal antibody to C. difficile toxin B that should be administered to patients at high risk of recurrence. Surgery is becoming less and less necessary and prevention with vaccines is under research. Probiotics have so far not been shown to be therapeutically or preventively effective. The therapeutic strategy should be based, rather than on the number of episodes, on the severity of the episodes and on their potential to recur. Some data point to the efficacy of oral vancomycin prophylaxis in patients who reccur CDI when systemic antibiotics are required again.

Hospital Infection Control: Clostridioides difficile

Clostridioides difficile remains a leading cause of healthcare-associated infection. Efforts at C. difficile prevention have been hampered by an increasingly complex understanding of transmission patterns and a high degree of heterogeneity among existing studies. Effective prevention of C. difficile infection requires multimodal interventions, including contact precautions, hand hygiene with soap and water, effective environmental cleaning, use of sporicidal cleaning agents, and antimicrobial stewardship. Roles for probiotics, avoidance of proton pump inhibitors, and isolation of asymptomatic carriers remain poorly defined.

In vitro Production and Immunogenicity of a Clostridium Difficile Spore-Specific BclA3 Glycopeptide Conjugate Vaccine

Abstract: The BclA3 glycoprotein is a major component of the exosporangial layer of Clostridium difficile spores and in this study we demonstrate that this glycoprotein is a major spore surface associated antigen. Here, we confirm the role of SgtA glycosyltransferase (SgtA GT) in BclA3 glycosylation and recapitulate this process by expressing and purifying SgtA GT fused to MalE, the maltose binding protein from Escherichia coli. In vitro assays using the recombinant enzyme and BclA3 synthetic peptides demonstrated that SgtA GT was responsible for the addition of β-O-linked GlcNAc to threonine residues of each synthetic peptide. These peptide sequences were selected from the central, collagen repeat region of the BclA3 protein. Following optimization of SgtA GT activity, we generated sufficient glycopeptide (10 mg) to allow conjugation to KLH (keyhole limpet hemocyanin) protein. Glycosylated and unglycosylated versions of these conjugates were then used as antigens to immunize rabbits and mice. Immune responses to each of the conjugates were examined by Enzyme Linked Immunosorbent Assay ELISA. Additionally, the BclA3 conjugated peptide and glycopeptide were used as antigens in an ELISA assay with serum raised against formalin-killed spores. Only the glycopeptide was recognized by anti-spore polyclonal immune serum demonstrating that the glycan moiety is a predominant spore-associated surface antigen. To determine whether antibodies to these peptides could modify persistence of spores within the gut, animals immunized intranasally with either the KLH-glycopeptide or KLH-peptide conjugate in the presence of cholera toxin, were challenged with R20291 spores. Although specific antibodies were raised to both antigens, immunization did not provide any protection against acute or recurrent disease.

Report from the World Health Organization's third Product Development for Vaccines Advisory Committee (PDVAC) meeting, Geneva, 8-10th June 2016

The third meeting of WHO's Product Development for Vaccines Advisory Committee (PDVAC) was held in June 2016, with a remit to revisit the pathogen areas for which significant progress has occurred since recommendations from the 2015 meeting, as well as to consider new advances in the development of vaccines against other pathogens. Since the previous meeting, significant progress has been made with regulatory approvals of the first malaria and dengue vaccines, and the first phase III trials of a respiratory syncytial virus (RSV) vaccine candidate has started in the elderly and pregnant women. In addition, PDVAC has also supported vaccine development efforts against important emerging pathogens, including Middle Eastern Coronavirus (MERS CoV) and Zika virus. Trials of HIV and tuberculosis vaccine candidates are steadily progressing towards pivotal data points, and the leading norovirus vaccine candidate has entered a phase IIb efficacy study. WHO's Immunization, Vaccine and Biologicals (IVB) department is actively working in several pathogen areas on the recommendation of PDVAC, as well as continuing horizon scanning for advances in the development of vaccines that may benefit low and middle income countries (LMICs), such as the recent licensure of the enterovirus 71 (EV71) vaccine in China. Following on from discussions with WHO's Strategic Advisory Group of Experts (SAGE) on Immunization, PDVAC will also look beyond licensure and consider data needs for vaccine recommendation and implementation to reduce the delay between vaccine approval and vaccine impact.

Proteomic profiling of precipitated Clostridioides difficile toxin A and B antibodies

Clostridioides difficile infection is the leading cause of nosocomial diarrhoea globally. Immune responses to toxins produced by C. difficile are important in disease progression and outcome. Here, we analysed the anti-toxin A and anti-toxin B serum antibody proteomes following natural infection or vaccination with a C. difficile toxoid A/toxoid B vaccine using a modified miniaturised proteomic approach based on de novo mass spectrometric sequencing. Analysis of immunoglobulin variable region (IgV) subfamily expression in immunoprecipitated toxin A and toxin B antibodies from four and seven participants of a vaccine trial, respectively, revealed a polyclonal proteome with restricted IGHV, IGKV and IGLV subfamily usage. No dominant IGHV subfamily was observed in the toxin A response, however the dominant anti-toxin B heavy (H)-chain was encoded by IGHV3-23. Light (L)-chain usage was convergent for both anti-toxin A and anti-toxin B proteomes with IGKV3-11, 3-15, 3-20 and 4-1 shared among all subjects in both cohorts. Peptide mapping of common IgV families showed extensive public and private amino acid substitutions. The cohort responses to toxin A and toxin B showed limited similarity in shared IGHV subfamilies. L-chain subfamily usage was more similar in the anti-toxin A and anti-toxin B responses, however the mutational signatures for each subfamily were toxin-dependent. Samples taken both post vaccination (n = 5) or at baseline, indicating previous exposure (n = 2), showed similar anti-toxin B IgV subfamily usage and mutational profiles. In summary, this study provides the first sequence-based proteomic analysis of the antibody response to the major disease-mediating toxins of C. difficile, toxin A and toxin B, and demonstrates that despite the potential for extreme diversity, the immunoglobulin repertoire can raise convergent responses to specific pathogens whether through natural infection or following vaccination.

Clostridioides difficile: diagnosis and treatments

Clostridioides difficile (formerly Clostridium) is a major cause of healthcare associated diarrhea, and is increasingly present in the community. Historically, C difficile infection was considered easy to diagnose and treat. Over the past two decades, however, diagnostic techniques have changed in line with a greater understanding of the physiopathology of C difficile infection and the use of new therapeutic molecules. The evolution of diagnosis showed there was an important under- and misdiagnosis of C difficile infection, emphasizing the importance of algorithms recommended by European and North American infectious diseases societies to obtain a reliable diagnosis. Previously, metronidazole was considered the reference drug to treat C difficile infection, but more recently vancomycin and other newer drugs are shown to have higher cure rates. Recurrence of infection represents a key parameter in the evaluation of new drugs, and the challenge is to target the right population with the adapted therapeutic molecule. In multiple recurrences, fecal microbiota transplantation is recommended. New approaches, including antibodies, vaccines, and new molecules are already available or in the pipeline, but more data are needed to support the inclusion of these in practice guidelines. This review aims to provide a baseline for clinicians to understand and stratify their choice in the diagnosis and treatment of C difficile infection based on the most recent data available.

Current and future trends in clostridioides (clostridium) difficile infection management

Current and future management of Clostridioides difficile infection (CDI) including antibiotic treatment is increasingly focused on preventive strategies, either prevention of recurrent CDI (rCDI) or primary prevention of CDI. In addition to newer narrow spectrum antibiotics and pulse dosing of antibiotic treatment, multiple widely differing approaches to prevention of CDI and rCDI are under clinical development or recently approved for clinical use. They include immunologics, both passive monoclonal antibodies and active vaccines targeted at C. difficile toxins, approaches to reduce antibiotic dysbiosis in the gut, microbiome restoration using fecal microbiome transplants (FMT) or biotherapeutic bacterial derivatives, and substitution of non-toxigenic C. difficile (NTCD) for toxigenic C. difficile. Newer antibiotics, monoclonal antibodies, and FMT are targeted at reducing rCDI whereas vaccines and reduction of antibiotic dysbiosis in the gut are targeted at prevention of primary CDI. Biotherapeutics may be used for prevention of either primary CDI or rCDI. Approaches such as monoclonal antibodies, FMT, and biotherapeutics provide rapid but transient preventive benefits, whereas vaccines require weeks to months to be effective, but will presumably provide long term prevention. More rapid but transient prevention strategies such as FMT and biotherapeutics could be used in combination with vaccines to provide both rapid and durable CDI prevention.

Vaccination against Clostridium difficile by Use of an Attenuated Salmonella enterica Serovar Typhimurium Vector (YS1646) Protects Mice from Lethal Challenge

Clostridium difficile disease is mediated primarily by toxins A and B (TcdA and TcdB, respectively). The receptor binding domains (RBD) of TcdA and TcdB are immunogenic, and anti-RBD antibodies are protective. Since these toxins act locally, an optimal C. difficile vaccine would generate both systemic and mucosal responses. We have repurposed an attenuated Salmonella enterica serovar Typhimurium strain (YS1646) to produce such a vaccine. Plasmid-based candidates expressing either the TcdA or TcdB RBD were screened. Different vaccine routes and schedules were tested to achieve detectable serum and mucosal antibody titers in C57BL/6J mice. When given in a multimodality schedule over 1 week (intramuscularly and orally [p.o.] on day 0 and p.o. on days 2 and 4), several candidates provided 100% protection against lethal challenge. Substantial protection (82%) was achieved with combined p.o. TcdA and TcdB vaccination alone (days 0, 2, and 4). These data demonstrate the potential of the YS1646-based vaccines for C. difficile and strongly support their further development.

Status of vaccine research and development for Clostridium difficile

Clostridium difficile associated disease is fundamentally associated with dysbiosis of the gut microbiome as a consequence of antibiotic use. This is because this sporulating, obligate anaerobe germinates and proliferates rapidly in the dysbiotic gut, which is an indirect consequence of their use. During its growth, C. difficile produces two toxins, toxin A (TcdA) and toxin B (TcdB), which are responsible for the majority of clinical symptoms associated with the disease. Three parenterally delivered vaccines, based on detoxified or recombinant forms of these toxins, have undergone or are undergoing clinical trials. Each offers the opportunity to generate high titres of toxin neutralising antibodies. Whilst these data suggest these vaccines may reduce primary symptomatic disease, they do not in their current form reduce the capacity of the organism to persist and shed from the vaccinated host. The current progress of vaccine development is considered with advantages and limitations of each highlighted. In addition, several alternative approaches are described that seek to limit C. difficile germination, colonisation and persistence. It may yet prove that the most effective treatments to limit infection, disease and spread of the organism will require a combination of therapeutic approaches. The potential use and efficacy of these vaccines in low and middle income countries will be depend on the development of a cost effective vaccine and greater understanding of the distribution and extent of disease in these countries.

Novel therapies and preventative strategies for primary and recurrent Clostridium difficile infections

Clostridium difficile is the leading infectious cause of antibiotic-associated diarrhea and colitis. C. difficile infection (CDI) places a heavy burden on the healthcare system, with nearly half a million infections yearly and an approximate 20% recurrence risk after successful initial therapy. The high incidence has driven new research on improved prevention such as the emerging use of probiotics, intestinal microbiome manipulation during antibiotic therapies, vaccinations, and newer antibiotics that reduce the disruption of the intestinal microbiome. While the treatment of acute C. difficile is effective in most patients, it can be further optimized by adjuvant therapies that improve the initial treatment success and decrease the risk of subsequent recurrence. Finally, the high risk of recurrence has led to multiple emerging therapies that target toxin activity, recovery of the intestinal microbial community, and elimination of latent C. difficile in the intestine. In summary, CDIs illustrate the complex interaction among host physiology, microbial community, and pathogen that requires specific therapies to address each of the factors leading to primary infection and recurrence.

Management of adult Clostridium difficile digestive contaminations: a literature review

Clostridium difficile infections (CDI) dramatically increased during the last decade and cause a major public health problem. Current treatments are limited by the high disease recurrence rate, severity of clinical forms, disruption of the gut microbiota, and colonization by vancomycin-resistant enterococci (VRE). In this review, we resumed current treatment options from official recommendation to promising alternatives available in the management of adult CDI, with regard to severity and recurring or non-recurring character of the infection. Vancomycin remains the first-line antibiotic in the management of mild to severe CDI. The use of metronidazole is discussed following the latest US recommendations that replaced it by fidaxomicin as first-line treatment of an initial episode of non-severe CDI. Fidaxomicin, the most recent antibiotic approved for CDI in adults, has several advantages compared to vancomycin and metronidazole, but its efficacy seems limited in cases of multiple recurrences. Innovative therapies such as fecal microbiota transplantation (FMT) and antitoxin antibodies were developed to limit the occurrence of recurrence of CDI. Research is therefore very active, and new antibiotics are being studied as surotomycin, cadazolid, and rinidazole.

Oral Immunization with Nontoxigenic Clostridium difficile Strains Expressing Chimeric Fragments of TcdA and TcdB Elicits Protective Immunity against C. difficile Infection in Both Mice and Hamsters

The symptoms of Clostridium difficile infection (CDI) are attributed largely to two C. difficile toxins, TcdA and TcdB. Significant efforts have been devoted to developing vaccines targeting both toxins through parenteral immunization routes. However, C. difficile is an enteric pathogen, and mucosal/oral immunization would be particularly useful to protect the host against CDI, considering that the gut is the main site of disease onset and progression. Moreover, vaccines directed only against toxins do not target the cells and spores that transmit the disease. Previously, we constructed a chimeric vaccine candidate, mTcd138, comprised of the glucosyltransferase and cysteine proteinase domains of TcdB and the receptor binding domain of TcdA. In this study, to develop an oral vaccine that can target both C. difficile toxins and colonization/adhesion factors, we expressed mTcd138 in a nontoxigenic C. difficile (NTCD) strain, resulting in strain NTCD_mTcd138. Oral immunization with spores of NTCD_mTcd138 provided mice full protection against infection with a hypervirulent C. difficile strain, UK6 (ribotype 027). The protective strength and efficacy of NTCD_mTcd138 were further evaluated in the acute CDI hamster model. Oral immunization with spores of NTCD_mTcd138 also provided hamsters significant protection against infection with 2 × 10⁴ UK6 spores, a dose 200-fold higher than the lethal dose of UK6 in hamsters. These results imply that the genetically modified, nontoxigenic C. difficile strain expressing mTcd138 may represent a novel mucosal vaccine candidate against CDI.

Clostridium difficile control measures: current and future methods for prevention

INTRODUCTION

Clostridium difficile is the most common cause of healthcare associated infection, and C. difficile infection (CDI) is associated with significant costs, morbidity, and mortality. One obstacle to preventing CDI is lack of high quality data on interventions to prevent CDI. This has led some to focus on areas, such as method of hand hygiene, unlikely to impact CDI incidence as much as others, such as contact precautions. In addition, existing strategies, although effective, do have limitations. Another challenge is the ability to rapidly, and accurately, diagnose CDI. Given these obstacles, new strategies to effectively prevent CDI are imperative to improve patient outcomes. Areas covered: Evidence of the interventions recommended by international scientific societies will be reviewed, as well as ongoing research on new strategies, such as screening for asymptomatic C. difficile carriage, microbiota sparing agents, bacteriocins and vaccines. Expert commentary: Current measures to prevent CDI are effective, but have significant limitations. Contact precautions and antimicrobial stewardship are likely the most effective of current prevention recommendations. Diagnostic assay utilization plays a role as well. New strategies to prevent CDI are needed, and, fortunately, several are being studied. Most likely a combination of approaches will be necessary to optimize CDI prevention.

Novel Chimeric Protein Vaccines Against Clostridium difficile Infection

Clostridium difficile infection (CDI) is the leading cause of world-wide nosocomial acquired diarrhea in adults. Active vaccination is generally accepted as a logical and cost-effective approach to prevent CDI. In this paper, we have generated two novel chimeric proteins; one designated Tcd169, comprised of the glucosyltransferase domain (GT), the cysteine proteinase domain (CPD), and receptor binding domain (RBD) of TcdB, and the RBD of TcdA; the other designated Tcd169FI, which contains Salmonella typhimurium flagellin (sFliC) and Tcd169. Both proteins were expressed in and purified from Bacillus megaterium. Point mutations were made in the GT (W102A, D288N) and CPD (C698) of TcdB to ensure that Tcd169 and Tcd169FI were atoxic. Immunization with Tcd169 or Tcd169Fl induced protective immunity against TcdA/TcdB challenge through intraperitoneal injection, also provided mice full protection against infection with a hyper-virulent C. difficile strain (BI/NAP1/027). In addition, inclusion of sFlic in the fusion protein (Tcd169Fl) enhanced its protective immunity against toxin challenge, reduced C. difficile numbers in feces from Tcd169Fl-immunized mice infected C. difficile. Our data show that Tcd169 and Tcd169FI fusion proteins may represent alternative vaccine candidates against CDI.

Clinical review of Clostridium difficile infection: an update on treatment and prevention

INTRODUCTION

Clostridium difficile infection (CDI) has become a significant healthcare-associated infection and is strongly associated with antibiotic use. Practice guidelines have recently been revised incorporating updated recommendations for diagnosis, treatment, and prevention.

AREAS COVERED

This review discusses updated aspects of CDI management. New and emerging pharmacologic options for treatment and prevention are reviewed.

EXPERT OPINION

Metronidazole is associated with lower rates of treatment success compared to vancomycin and should no longer be used as primary therapy for the first episode of CDI or recurrent disease. Vancomycin or fidaxomicin are now recommended for first-line therapy for most cases of CDI. Fecal microbiota transplant is effective and safe for the treatment of recurrent CDI. Evidence supports the use of fidaxomicin and bezlotoxumab for prevention of recurrent CDI; however, the costs associated with these therapies may limit their use. Validated risk prediction tools are needed to identify patients most likely to benefit from these treatments. Future advancements in microbiota targeting treatments will emerge as promising alternatives to standard CDI treatments. Antibiotic stewardship and infection control measures will remain essential components for CDI management.

Current clostridium difficile treatments: Lessons that need to be learned from the clinical trials

Clostridium difficile infection (CDI) is the most common infectious disease cause of nosocomial diarrhea in adults in developed countries. Judging from the clinical trials on drugs used in CDIs, no approved treatment for recurrences exists, possibly indicating that a combination of treatment approaches are mandatory especially in severe infections, with current studies not being fully representative. Among the new strategies researched intensively fidaxomicin is presented, which demonstrates reduced CDI recurrences. Moreover, biotherapeutic strategies, mainly fecal microbiota transplantation but also competitive inhibition with non-toxigenic strains of C. difficile, and finally monoclonal antibodies against C. difficile toxins which offer protection against recurrences. Careful interpretation of the results based on lessons learned from previous trials conducted seems crucial. Questions are raised regarding how the results of future studies regarding new strategies researched will be managed and interpreted especially with regard to recurrence management as relevant data must be monitored for at least 30 days after end of treatment.