Effects of Clostridium difficile toxin A and B on human T lymphocyte migration

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.

Long-term expression changes of immune-related genes in prostate cancer after radiotherapy

The expression of immune-related genes in cancer cells can alter the anti-tumor immune response and thereby impact patient outcomes. Radiotherapy has been shown to modulate immune-related genes dependent on the fractionation regimen. To identify long-term changes in gene expression after irradiation, PC3 (p53 deleted) and LNCaP (p53 wildtype) prostate cancer cells were irradiated with either a single dose (SD, 10 Gy) or a fractionated regimen (MF) of 10 fractions (1 Gy per fraction). Whole human genome arrays were used to determine gene expression at 24 h and 2 months after irradiation. Immune pathway activation was analyzed with Ingenuity Pathway Analysis software. Additionally, 3D colony formation assays and T-cell cytotoxicity assays were performed. LNCaP had a higher basal expression of immunogenic genes and was more efficiently killed by cytotoxic T-cells compared to PC3. In both cell lines, MF irradiation resulted in an increase in multiple immune-related genes immediately after irradiation, while at 2 months, SD irradiation had a more pronounced effect on radiation-induced gene expression. Both immunogenic and immunosuppressive genes were upregulated in the long term in PC3 cells by a 10 Gy SD irradiation but not in LNCaP. T-cell-mediated cytotoxicity was significantly increased in 10 Gy SD PC3 cells compared to the unirradiated control and could be further enhanced by treatment with immune checkpoint inhibitors. Irradiation impacts the expression of immune-related genes in cancer cells in a fractionation-dependent manner. Understanding and targeting these changes may be a promising strategy for primary prostate cancer and recurrent tumors.

Clostridioides difficile Toxin CDT Induces Cytotoxic Responses in Human Mucosal-Associated Invariant T (MAIT) Cells

Clostridioides difficile is the major cause of antibiotic-associated colitis (CDAC) with increasing prevalence in morbidity and mortality. Severity of CDAC has been attributed to hypervirulent C. difficile strains, which in addition to toxin A and B (TcdA, TcdB) produce the binary toxin C. difficile transferase (CDT). However, the link between these toxins and host immune responses as potential drivers of immunopathology are still incompletely understood. Here, we provide first experimental evidence that C. difficile toxins efficiently activate human mucosal-associated invariant T (MAIT) cells. Among the tested toxins, CDT and more specifically, the substrate binding and pore-forming subunit CDTb provoked significant MAIT cell activation resulting in selective MAIT cell degranulation of the lytic granule components perforin and granzyme B. CDT-induced MAIT cell responses required accessory immune cells, and we suggest monocytes as a potential CDT target cell population. Within the peripheral blood mononuclear cell fraction, we found increased IL-18 levels following CDT stimulation and MAIT cell response was indeed partly dependent on this cytokine. Surprisingly, CDT-induced MAIT cell activation was found to be partially MR1-dependent, although bacterial-derived metabolite antigens were absent. However, the role of antigen presentation in this process was not analyzed here and needs to be validated in future studies. Thus, MR1-dependent induction of MAIT cell cytotoxicity might be instrumental for hypervirulent C. difficile to overcome cellular barriers and may contribute to pathophysiology of CDAC.

Detoxification of toxin A and toxin B by copper ion-catalyzed oxidation in production of a toxoid-based vaccine against Clostridioides difficile

Clostridioides difficile infections (CDI) has emerged worldwide as a serious antimicrobial-resistant healthcare-associated disease resulting in diarrhea and pseudomembranous colitis. The two cytotoxic proteins, toxin A (TcdA) and toxin B (TcdB) are the major virulence factor responsible for the disease symptoms. We examined time-dependent oxidative detoxification of TcdA and TcdB using different molar ratios of protein:Cu^2+:H₂O₂. The metal-catalyzed oxidation (MCO) reaction in molar ratios of 1:60:1000 for protein:Cu^2+:H₂O₂ at pH 4.5 resulted in a significant 6 log₁₀ fold reduction in cytotoxicity after 120-min incubation at 37 °C. Circular dichroism revealed that MCO-detoxified TcdA and TcdB had secondary and tertiary structural folds similar to the native proteins. The conservation of immunogenic epitopes of both proteins was tested using monoclonal antibodies in an ELISA, comparing our MCO-detoxification approach to a conventional formaldehyde-detoxification method. The oxidative detoxification of TcdA and TcdB led to an average 2-fold reduction in antibody binding relative to native proteins, whereas formaldehyde cross-linking resulted in 3-fold and 5-fold reductions, respectively. Finally, we show that mice immunized with a vaccine consisting of MCO-detoxified TcdA and TcdB were fully protected against disease symptoms and death following a C. difficile infection and elicited substantial serum IgG responses against both TcdA and TcdB. The results of this study present copper ion-catalyzed oxidative detoxification of toxic proteins as a method highly suitable for the rapid production of safe, immunogenic and irreversible toxoid antigens for future vaccine development and may have the potential for replacing cross-linking reagents like formaldehyde.

Microbiota in Clostridioides difficile-Associated Diarrhea: Comparison in Recurrent and Non-Recurrent Infections

Clostridioides difficile infection (CDI) is the leading cause of antibiotic-associated diarrhea, especially in hospitalized elderly patients, representing a global public health concern. Clinical presentations vary from mild diarrhea to severe pseudomembranous colitis that may progress to toxic megacolon or intestinal perforation. Antibiotic therapy is recognized as a risk factor and exacerbates dysbiosis of the intestinal microbiota, whose role in CDI is increasingly acknowledged. A clinically challenging complication is the development of recurrent disease (rCDI). In this study, using amplicon metagenomics, we compared the fecal microbiota of CDI and rCDI patients (sampled at initial and recurrent episode) and of non-infected controls. We also investigated whether CDI severity relates to specific microbiota compositions. rCDI patients showed a significantly decreased bacterial diversity as compared to controls (p < 0.01). The taxonomic composition presented significant shifts: both CDI and rCDI patients displayed significantly increased frequencies of Firmicutes, Peptostreptococcaceae, Clostridium XI, Clostridium XVIII, and Enterococcaceae. Porphyromonadaceae and, within it, Parabacteroides displayed opposite behaviors in CDI and rCDI, appearing discriminant between the two. Finally, the second episode of rCDI was characterized by significant shifts of unclassified Clostridiales, Escherichia/Shigella and Veillonella. No peculiar taxa composition correlated with the severity of infection, likely reflecting the role of host-related factors in determining severity.

Clostridioides difficile Infection Induces an Inferior IgG Response to That Induced by Immunization and Is Associated with a Lack of T Follicular Helper Cell and Memory B Cell Expansion

The intracellularly active bacterial toxin TcdB is a major Clostridioides difficile virulence factor that contributes to inflammation and tissue damage during disease. Immunization with an inactive TcdB fragment prevents C. difficile infection (CDI)-associated pathology. The protective immune response against inactive TcdB involves development of antigen-specific memory B cells and long-lived plasma cells that encode TcdB-neutralizing antibodies. Unlike the response to inactive TcdB, very little is known about the host humoral immune response to C. difficile and TcdB during primary and recurrent infection. Here, we used a murine model of C. difficile disease recurrence to demonstrate that an initial infection induced a serum IgM and mucosal IgA response against the toxin, but a low serum IgG response, which is associated with a lack of protection against disease during reinfection. Infection induced a partial expansion of the T follicular helper cell compartment, essential for B cell memory responses, and, consistent with that, failed to significantly expand the memory B cell compartment. Further, infection failed to stimulate the memory B cell compartment in preimmunized mice, although they were protected against associated disease. These results delineate the key humoral immune events that follow primary and recurrent C. difficile infection and provide a compelling inverse correlation between B cell memory and disease recurrence.

Sputum from chronic obstructive pulmonary disease patients inhibits T cell migration in a microfluidic device

Chronic obstructive pulmonary disease (COPD) is a common lung disease characterized by narrowed airways, resulting in serious breathing difficulty. Previous studies have demonstrated that inflammatory infiltration of leukocytes in the airway is associated with the pathogenesis of COPD. In the present study, we employed a microfluidic approach to assess the effect of COPD sputum on activated human peripheral blood T cell migration and chemotaxis under well-controlled gradient conditions. Our results showed considerable basal migration of T cells derived from peripheral blood of COPD patients and healthy controls in the medium control groups. By contrast, the migration of T cells from COPD patients and healthy controls was significantly inhibited in the presence of a gradient of sputum supernatant from COPD patients. Furthermore, chemotaxis of T cells from COPD patients or healthy subjects toward an SDF-1α gradient was clearly inhibited by sputum samples from the COPD patients. The inhibition effect revealed by the microfluidic cell migration experiments provides new information about the complex involvement of T cell trafficking in COPD.

Effects of Clostridium difficile toxin A on K562/A02 cell proliferation, apoptosis and multi-drug resistance

The aim of the present study was to investigate the cytotoxic effect and multi-drug resistance (MDR) of Clostridium difficile toxin A (TcdA) on K562/A02 cells, and understand its underlying molecular pathways. K562/A02 cells were treated with TcdA at different concentrations for 24, 48 and 72 h, and the inhibition effect and drug resistance of TcdA on K562/A02 cell proliferation was assessed by methyl thiazolyl tetrazolium colorimetric assay. Furthermore, cell cycle-apoptosis was analyzed by flow cytometry, P-glycoprotein (P-gp) expression was determined by western blot analysis and caspase-3 activity was measured using a caspase-3 activity kit. TcdA inhibited K562/A02 cell proliferation in a time- and dose-dependent manner. The inhibition rate of K562/A02 cells reached 8.76±0.76, 28.55±0.43, 47.89±0.27, 58.08±0.06 and 57.70±0.79% following treatment with 50, 100, 200, 400 and 800 ng/ml TcdA, respectively, for 24 h. K562/A02 cells in the G0/G1 phase increased and cells in the S phase decreased following treatment with TcdA (P<0.05), and the apoptotic rates in the 200 and 400 ng/ml concentration groups were 14.05 and 22.89%, respectively. In addition, TcdA (50 ng/ml) significantly inhibited the proliferation of K562/A02 cells and reduced the half maximal inhibitory concentration of these drugs in combination with chemotherapy drugs. The reversal folds were 3.09, 2.89 and 2.79, respectively. Furthermore, TcdA treatment was associated with the upregulation of P-gp in K562/A02 cells, and caspase-3 activity was observed to increase in K562/A02 cells following TcdA treatment, when compared with untreated controls (P<0.05). These findings suggested that TcdA may be able to inhibit K562/A02 cell growth, induce cell apoptosis by decreasing P-gp levels and caspase-3 activation, and partially reverse MDR. Further studies are required to evaluate the potential of TcdA as a candidate for the chemotherapy of hematologic malignancies.

Candidemia in Patients with Body Temperature Below 37°C and Admitted to Internal Medicine Wards: Assessment of Risk Factors

BACKGROUND

An increasing number of candidemia episodes has been reported in patients cared for in internal medicine wards. These usually older and frail patients may not be suspected as having candidemia because they lack fever at the onset of the episode. To identify the risk factors associated with the lack of fever at the onset of candidemia (ie, the collection of the first positive blood culture for Candida spp.) in patients cared for in internal medicine wards, we compared 2 group of patients with or without fever.

METHODS

We retrospectively review data charts from 3 tertiary care, university hospitals in Italy, comparing patients with or without fever at onset of candidemia. Consecutive candidemic episodes in afebrile patients and matched febrile controls were identified during the 3-year study period. Patient baseline characteristics and several infection-related variables were examined. Random forest analysis was used, given the number of predictors to be considered and the potential complexity of their relations with the onset of fever.

RESULTS

We identified 147 candidemic episodes without fever at onset and 147 febrile candidemia episodes. Factors associated with the lack of fever at onset of candidemia were diabetes, Clostridium difficile infection, and a shorter delta time from internal medicine wards admission to the onset of candidemia. The only variable associated with fever was the use of intravascular devices. Quite unexpectedly, antifungal therapy was administered more frequently to patients without fever, and no differences on 30-day mortality rate were documented in the 2 study groups.

CONCLUSIONS

Clinicians should be aware that an increasing number of patients with invasive candidiasis cared for in internal medicine wards may lack fever at onset, especially those with diabetes and C. difficile infection. Candidemia should be suspected in patients with afebrile systemic inflammatory response syndrome or in worsening clinical condition: blood cultures should be taken, and a timely and appropriate antifungal therapy should be considered.

Clostridium difficile infection: A brief update on emerging therapies

PURPOSE

Established and investigational antibiotic, monoclonal antibody, vaccine, and microbe-based approaches to the prevention and treatment of Clostridium difficile infection (CDI) are reviewed.

SUMMARY

CDI is increasingly prevalent in the United States and other countries, particularly among hospitalized patients and the elderly, who are at high risk for potentially fatal CDI-related enterotoxic diarrhea. Established therapies for CDI such as vancomycin and metronidazole (an off-label use) are limited by poor efficacy and high recurrence rates. An investigational antibiotic with potent in vitro activity against all C. difficile strains (including the hypervirulent BI/NAP1/027 strain) has yielded encouraging results in early clinical trials. Another promising approach involves the use of monoclonal antibodies with selective activity against toxins responsible for CDI-associated diarrhea; in a small Phase II clinical trial, a single monoclonal antibody infusion in combination with vancomycin or metronidazole therapy was more effective than antibiotic therapy alone in preventing CDI relapse. Other emerging approaches to CDI treatment and prophylaxis include the use of vaccines against C. difficile toxins (several C. difficile-targeted vaccines are under development in Europe and the United States); microbe-based strategies such as fecal microbiota transplants, "microbial ecosystem therapeutics," and probiotic supplements; and an investigational encapsulated form of β-lactamase designed to prevent C. difficile colonization from progressing to CDI.

CONCLUSION

The current antibiotic therapies for CDI, mainly vancomycin and (off-label) metronidazole and the newer agent fidaxomicin, have limitations with respect to efficacy, recurrence rates, and adverse effects, but a variety of promising approaches are emerging.

Clostridium difficile infection in the postcolectomy patient

Clostridium difficile infection (CDI) after total colectomy has been increasingly recognized over the past decade. C. difficile enteritis (CDE) is a rare occurrence, whereas C. difficile pouchitis (CDP) has been reported in approximately 10% of symptomatic patients seen at a referral center for pouch dysfunction. Similar to colonic CDI in the general population, antibiotic use and comorbid diseases may be risk factors for CDE. In contrast, the postoperative use of antibiotics does not seem to be associated with CDP, whereas male gender, recent hospitalization, and presurgery antibiotic use were shown to be risk factors for CDP. C. difficile is capable of colonizing all intestinal sites, including the ileal pouch. Similarities with the colon at physiological and cellular levels may contribute to the susceptibility of the ileal pouch to CDI. Postcolectomy CDI likely represents a disease spectrum from asymptomatic colonization to severe symptomatic infection. CDI should be considered in ostomy patients with fever and increased ileostomy output and in ileal pouch patients with a change in "normal" symptom pattern or chronic antibiotic-refractory pouchitis. Sensitive and specific methods for detection of CDI are available, and endoscopy is useful in evaluating the patient with suspected CDE or CDP, although pseudomembranes are typically absent. Vancomycin is used as the first-line therapy for CDP and may be warranted for patients with inflammatory bowel disease with CDE. Fecal microbiota transplantation has found its use in the management of severe or antibiotic refractory CDP, but this approach requires evaluation for the management of refractory CDE.

Clostridium difficile recurrence is characterized by pro-inflammatory peripheral blood mononuclear cell (PBMC) phenotype

Clostridium difficile infection (CDI) is a prevalent nosocomial and increasingly community-acquired problem. Little is known about the productive cellular response in patients. We used flow cytometry to define inflammatory (Th1 and Th17) and regulatory [Foxp3(+) T-regulatory (Treg)] cells present in circulating peripheral blood mononuclear cells (PBMC) from CDI patients. We consented 67 inpatients that tested either positive or negative for CDI and 16 healthy controls and compared their PBMC phenotypes. PBMC were collected, isolated, and stained for CD3, CD8 and either IL17 (Th17), IFN-γ (Th1) or Foxp3 (Treg) and analysed using flow cytometry. Twenty thousand events were collected in the lymphocyte gate (gate 1) and T-cell phenotypes were defined. CDI patients who clear the primary initial infection have greater numbers of non-CD3 PBMC. CDI patients who develop recurrence of CDI have a greater percentage of CD3(+)CD8(+), CD3(+)CD4(+)Foxp3 and fewer low granular CD3(-)Foxp3(+) PBMC. These patients have greater numbers of IFN-γ-producing lymphocytes, as well as PBMC phenotypes represented by increased IFN-γ- and IL17-co-expressing CD4(+)CD3(+). This initial pro-inflammatory phenotype decreases with repeated recurrence, demonstrating importance of timing of sample collection and history of symptoms. Patients with a history of recurrence had increased Foxp3(+)CD3(+)CD4(+) and IL17(+)CD3(+)CD4(+) populations. Hence, CDI recurrence is hallmarked by greater numbers of circulating CD3(+) lymphocytes skewed towards a Th1/Th17 inflammatory population as well as possible immune plasticity (Th17/Treg).

The roles of toxin A and toxin B in Clostridium difficile infection: insights from the gnotobiotic piglet model

We recently published our findings indicating that anti-TcdB antibodies were effective as treatment for C. difficile infection, but that anti-TcdA actually worsened prognosis in the gnotobiotic piglet model. To further investigate the roles of the two toxins, we administered purified toxins separately or together, systemically, to piglets and found that both toxins, either alone or together, are able to elicit severe lesions systemically and are also able to cross into the gut lumen and cause large intestinal lesions typical of infection. We also found that anti-TcdA administered before systemic challenge with TcdA again did not protect from development of disease, but, in this case, did not appear to worsen prognosis. Further work is still needed, but these findings add to the growing knowledge regarding the roles of the C. difficile toxins.