Questionable Efficacy of Therapeutic Antibodies in the Treatment of Anthrax.

Inhalational anthrax caused by Bacillus anthracis, a spore-forming Gram-positive bacterium, is a highly lethal infection. Antibodies targeting the protective antigen (PA) binding component of the toxins have recently been authorized as an adjunct to antibiotics, although no conclusive evidence demonstrates that anthrax antitoxin therapy has any significant benefit. We discuss here the rational basis of anti-PA development regarding the pathogenesis of the disease. We argue that inductive reasoning may induce therapeutic bias. We identified anthrax animal model analysis as another bias. Further studies are needed to assess the benefit of anti-PA antibodies in the treatment of inhalational anthrax, while a clearer consensus should be established around what evidence should be proven in an anthrax model.

Monoclonal antibody-based therapies for bacterial infections.

PURPOSE OF REVIEW: This review highlights recent developments in the development of monoclonal antibodies to treat bacterial disease, including preclinical advances and the status of current clinical trials. RECENT FINDINGS: Monoclonal antibody (mAb) therapy is becoming increasingly promising in the infectious disease field. Though bacterial exotoxins continue to be a mainstay of mAb targets, searches for protein targets on the surface of bacteria have uncovered new mechanisms of antibody-mediated action against bacteria. Additionally, surveys of the polysaccharide serotype prevalence among antibiotic-resistant bacterial populations have yielded opportunities to leverage human selective pressures to our clinical advantage. Several mAb candidates are progressing through clinical development with great promise, especially those with structures altered to provide maximum benefit. Although other clinical trials have recently proved unsuccessful, these failures and lessons from immune profiling provide opportunities to understand how vulnerabilities of certain targets may change in different disease states. SUMMARY: Despite the hurdles of identifying effective targets and understanding how mAbs provide protection within different infections, we show that the progress made in these fields is a positive indication of mAbs becoming more widely accepted as the future for treating bacterial infections.

Holistic Approach in Patients With Presumed Lyme Borreliosis Leads to Less Than 10% of Confirmation and More Than 80% of Antibiotic Failures.

BACKGROUND: There is no precise idea whether patients with chronic symptoms attributed to Lyme borreliosis (LB) have LB or another disease. METHODS: We evaluated patients consulting for a presumed LB with a holistic approach including presumptive treatment. We included symptomatic patients consulting for presumed LB. They were classified as confirmed LB when they met four criteria, and possible LB if three with a positive clinical response to presumptive treatment. RESULTS: Amongst the 301 patients, 275 (91%) were exposed to tick bites, and 165 (54%) were bitten by a tick. At presentation, 151 patients (50.1%) had already been treated with a median of one (1-22) course of antimicrobials, during 34 (28-730) days. Median number of symptoms was three (1-12) with a median duration of 16 (1-68) months. Median number of signs was zero (0-2). ELISA was positive in 84/295 (28.4%) for IgM and 86/295 (29.1%) for IgG, and immunoblot was positive in 21/191 (10.9%) for IgM and 50/191 (26.1 %) for IgG. Presumptive treatment after presentation failed in 46/88 patients (52%). Diagnosis of LB was confirmed in 29 patients (9.6%), and possible in 9 (2.9%). Of the 243 patients with non-LB diagnosis, diseases were psychological, musculoskeletal, neurological or other origin in 76 (31.2%), 48 (19.7%), 37 (15.2%) and 82 (33.7%) patients respectively. Patients with other diseases were significantly younger, having more symptoms, longest duration of symptoms, less clinical signs and less frequent LB positive serologies. CONCLUSIONS: Overdiagnosis and overtreatment of LB is worsening. Health authorities should investigate this phenomenon.

Immune stealth-driven O2 serotype prevalence and potential for therapeutic antibodies against multidrug resistant Klebsiella pneumoniae.

Emerging multidrug-resistant bacteria are a challenge for modern medicine, but how these pathogens are so successful is not fully understood. Robust antibacterial vaccines have prevented and reduced resistance suggesting a pivotal role for immunity in deterring antibiotic resistance. Here, we show the increased prevalence of Klebsiella pneumoniae lipopolysaccharide O2 serotype strains in all major drug resistance groups correlating with a paucity of anti-O2 antibodies in human B cell repertoires. We identify human monoclonal antibodies to O-antigens that are highly protective in mouse models of infection, even against heavily encapsulated strains. These antibodies, including a rare anti-O2 specific antibody, synergistically protect against drug-resistant strains in adjunctive therapy with meropenem, a standard-of-care antibiotic, confirming the importance of immune assistance in antibiotic therapy. These findings support an antibody-based immunotherapeutic strategy even for highly resistant K. pneumoniae infections, and underscore the effect humoral immunity has on evolving drug resistance.

Prophylactic Efficacy of Hyperimmune Bovine Colostral Antiadhesin Antibodies Against Enterotoxigenic Escherichia coli Diarrhea: A Randomized, Double-Blind, Placebo-Controlled, Phase 1 Trial.

Background: Tip-localized adhesive proteins of bacterial fimbriae from diverse pathogens confer protection in animal models, but efficacy in humans has not been reported. Enterotoxigenic Escherichia coli (ETEC) commonly elaborate colonization factors comprising a minor tip adhesin and major stalk-forming subunit. We assessed the efficacy of antiadhesin bovine colostral IgG (bIgG) antibodies against ETEC challenge in volunteers. Methods: Adults were randomly assigned (1:1:1) to take oral hyperimmune bIgG raised against CFA/I minor pilin subunit (CfaE) tip adhesin or colonization factor I (CFA/I) fimbraie (positive control) or placebo. Two days before challenge, volunteers began a thrice-daily, 7-day course of investigational product administered in sodium bicarbonate 15 minutes after each meal. On day 3, subjects drank 1 × 109 colony-forming units of colonization factor I (CFA/I)-ETEC strain H10407 with buffer. The primary efficacy endpoint was diarrhea within 120 hours of challenge. Results: After enrollment and randomization, 31 volunteers received product, underwent ETEC challenge, and were included in the per protocol efficacy analysis. Nine of 11 placebos developed diarrhea, 7 experiencing moderate to severe disease. Protective efficacy of 63% (P = .03) and 88% (P = .002) was observed in the antiadhesin bIgG and positive control groups, respectively. Conclusions: Oral administration of anti-CFA/I minor pilin subunit (CfaE) antibodies conferred significant protection against ETEC, providing the first clinical evidence that fimbrial tip adhesins function as protective antigens.

Efficacy of the Rabbit Polyclonal Anti-leptospira Antibody against Homotype or Heterotype Leptospira Infection in Hamster.

Leptospirosis, caused by Leptospira, is one of the most important of neglected emerging zoonotic diseases that has important impacts on public health worldwide. Polyclonal antibody (pcAb) therapy is a potential method to process a series of pathogens for which there are limited determination of treatment, such as leptospirosis. First, we evaluated the efficacy of pcAb, derived from the sera of rabbits inoculated with Leptospira, against homotype (Leptospira interrogans serovar Lai) or heterotype (Leptospira interrogans serovar Autumnalis) Leptospira infection in a lethal hamster model. The pcAb treatment improved survival compared to the controls. The histopathology's of the infected kidney, liver and lung were also examined by hematoxylin and eosin staining. Using real-time quantitative PCR, we determined that most of the leptospires in the primary organs were almost completely removed by pcAb. In the second experiment, treatments, including antibiotic, pcAb, and combination, were started immediately after occurrence of the first serious sickness mouse in any group. No significant difference in survival rate between pcAb group and antibiotic group was found, but the combination therapy group significantly improved survival rate compared to the others (P<0.05). We conclude that the rabbit pcAb treatment may cure both the homotype and the heterotype lethal Leptospira infections in hamster, and combination therapy improved survival compared to antibiotic group in the late treatment of homotype leptospirosis.

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

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

Preclinical Efficacy of Clumping Factor A in Prevention of Staphylococcus aureus Infection.

UNLABELLED: Treatment of Staphylococcus aureus infections has become increasingly difficult because of the emergence of multidrug-resistant isolates. Development of a vaccine to prevent staphylococcal infections remains a priority. To determine whether clumping factor A (ClfA) is a good target protein for inclusion in a multivalent vaccine, we evaluated its efficacy in a variety of relevant staphylococcal infection models, challenging with different S. aureus strains. ClfA adsorbed to Alhydrogel and mixed with Sigma Adjuvant System was more immunogenic and stimulated a more robust Th17 response than ClfA administered with alum alone. ClfA immunization induced the production of functional antibodies in rabbits and mice that blocked S. aureus binding to fibrinogen and were opsonic for S. aureus strains that produced little or no capsular polysaccharide. Mice immunized with ClfA showed a modest reduction in the bacterial burden recovered from subcutaneous abscesses provoked by S. aureus USA300 strain LAC. In addition, the ClfA vaccine reduced lethality in a sepsis model following challenge with strain Newman, but not ST80. Vaccination with ClfA did not protect against surgical wound infection, renal abscess formation, or bacteremia. Passive immunization with antibodies to ClfA did not protect against staphylococcal bacteremia in mice or catheter-induced endocarditis in rats. Some enhancement of bacteremia was observed by ClfA immunization or passive administration of ClfA antibodies when mice were challenged by the intraperitoneal route. Although rodent models of staphylococcal infection have their limitations, our data do not support the inclusion of ClfA in an S. aureus multivalent vaccine. IMPORTANCE: Antibiotics are often ineffective in eradicating Staphylococcus aureus infections, and thus, a preventative vaccine is sorely needed. Two single-component vaccines and two immunoglobulin preparations failed to meet their designated endpoints in phase III clinical trials. Importantly, recipients of an S. aureus surface protein (iron surface determinant B) vaccine who developed a staphylococcal infection experienced a higher rate of multiorgan failure and mortality than placebo controls, raising safety concerns. Multicomponent S. aureus vaccines have now been generated, and several include surface protein clumping factor A (ClfA). We immunized mice with ClfA and generated a robust T cell response and serum antibodies that were functional in vitro. Nonetheless, ClfA was not protective in a number of relevant animal models of S. aureus infection, and high levels of ClfA antibodies enhanced bacteremia when mice were challenged with community-acquired methicillin-resistant S. aureus strains. Evidence supporting ClfA as a vaccine component is lacking.

Therapeutic approaches for Clostridium difficile infections.

Metronidazole and vancomycin remain the front-line therapies for most Clostridium difficile infections (CDI). However, recurrent CDI occurs in ∼ 25% of patients, causing significant morbidity and mortality and healthcare costs. For this population, traditional antibiotic therapies fail and new treatment options are greatly needed. The US Food and Drug Administration recently approved fidaxomicin for CDI treatment. This narrow-spectrum antibiotic preserves the normal gut microbiota and shows promise as a treatment for severe and recurrent CDI. Monoclonal antibodies and vaccines directed against toxin are currently in clinical trials and represent alternative, non-antibiotic therapies. Less traditional therapeutic interventions include bacteriotherapy with non-toxigenic C. difficile and fecal transplant. This commentary will provide an overview of current and forthcoming CDI therapies.

Randomized control trials using a tablet formulation of hyperimmune bovine colostrum to prevent diarrhea caused by enterotoxigenic Escherichia coli in volunteers.

OBJECTIVE: Enterotoxigenic Escherichia coli (ETEC) is the leading cause of travelers' diarrhea. The aim of this study was to investigate the ability of a powdered extract of hyperimmune bovine colostrum to protect against diarrhea in volunteers challenged with ETEC. MATERIALS AND METHODS: Tablets were manufactured from a colostrum extract from cattle immunized with 14 ETEC strains, including serogroup O78. Two separate randomized, double-blind, placebo-controlled trials involving 90 healthy adult volunteers were performed to investigate the ability of different tablet formulations to protect against diarrhea following an oral challenge with an O78 ETEC strain. RESULTS: The first study with 30 participants evaluated the efficacy of tablets, containing 400 mg of colostrum protein, taken thrice daily with bicarbonate buffer. This regimen conferred 90.9% protection against diarrhea in the group receiving the active preparation compared with the placebo group (p = 0.0005). The second study examined the efficacy of tablets containing 400 mg colostrum protein given with buffer (83.3% protection; p = 0.0004) or without buffer (76.7% protection; p = 0.007), and tablets containing 200 mg colostrum protein given without buffer (58.3% protection; p = 0.02), compared with placebo. The difference between buffered and unbuffered treatments was not significant (p > 0.1). CONCLUSIONS: Active tablet formulations were significantly more effective than placebo in protecting volunteers against the development of diarrhea caused by ETEC. These results suggest that administration of a tablet formulation of hyperimmune bovine colostrum containing antibodies against ETEC strains may reduce the risk of travelers' diarrhea.

Immunotherapeutic strategies to combat staphylococcal infections.

Antibiotic-resistant staphylococci are the leading cause of nosocomial infections in many hospitals around the world. Meanwhile, methicillin-resistant Staphylococcus aureus (MRSA) spread also in the community where highly virulent strains infect healthy adults that have no predisposing risk factors. Although a few novel antibiotics have been recently introduced into clinical practice, the search for alternative strategies to efficiently combat staphylococcal infections is urgently demanded to decrease the enormous burden caused by pathogenic staphylococci. In particular, immunological strategies based on vaccine development or therapeutic antibodies may significantly enhance the efficiency of anti-staphylococcal therapy. Most approaches are directed against surface components of staphylococci such as cell wall-linked adhesins, teichoic acids, capsule, the biofilm component PIA/PNAG, or soluble virulence determinants such as alpha-toxin, Panton-Valentine leukocidin, or superantigenic enterotoxins. Although 2 recent clinical trials have failed, several novel promising vaccines and therapeutic antibodies are currently in preclinical and clinical development.

Treatment of anthrax infection with combination of ciprofloxacin and antibodies to protective antigen of Bacillus anthracis.

Currently there is no effective treatment for inhalational anthrax beyond administration of antibiotics shortly after exposure. There is need for new, safe and effective treatments to supplement traditional antibiotic therapy. Our study was based on the premise that simultaneous inhibition of lethal toxin action with antibodies and blocking of bacterial growth by antibiotics will be beneficial for the treatment of anthrax. In this study, we tested the effects of a combination treatment using purified rabbit or sheep anti-protective antigen (PA) antibodies and the antibiotic ciprofloxacin in a rodent anthrax model. In mice infected with a dose of Bacillus anthracis Sterne strain corresponding to 10 LD(50), antibiotic treatment with ciprofloxacin alone only cured 50% of infected animals. Administration of anti-PA IgG in combination with ciprofloxacin produced 90-100% survival. These data indicate that a combination of antibiotic/immunoglobulin therapy is more effective than antibiotic treatment alone in a rodent anthrax model.

[Evaluation on monkeys of reactogenicity and effectiveness of the complex immunoglobulin preparation formulation]. / Otsenka na obez'ianakh reaktogennocti i éffektivnosti lekarstvennykh form kompleksnogo immunoglobulinovogo preparata.

Experiments on 75 monkeys, 20--healthy and 75--with diarrhea, showed that ready medicinal forms of the complex immunoglobulin preparation in tablets, capsules or in a dried form (vials) were safe, well tolerated, clinically and bacteriologically effective. When used simultaneously with antiparasitic treatment, this preparation, irrespective of the kind of its ready medicinal form, showed high curative effect (80-90%). The diarrhea ceasing was accompanied by the gradual normalization of intestinal microbiocenosis (an increased concentrations of Escherichia coli and Bifidobacterium, a decreased amount of opportunistic bacteria). The complex method of the treatment of diarrhea in monkeys (antibiotics, trichopol, phage and probiotics) made it possible to achieve curative effect only in 60% of cases, which required the additional course of treatment, namely the use of rehydration therapy.

Antibacterial effects of Carica papaya on common wound organisms [abstract]

OBJECTIVE: The objective was to investigate the antibacterial activity of the crude Carica papaya preparations as used by nurses, on gram negative and gram positive organisms; to determine which part and stage of maturity of the fruit yielded the best antibacterial activity, and determine the effects of storage conditions on the observed activity. METHODS: The pathogens commonly found in human wounds were obtained from the Microbiology Department, University of the West Indies, Biochemistry Section, The University of the West Indies and the Jamaican Bureau of Standards. Cultures were routinely maintained in nutrient agar slants at 4§c. Extracts were obtained by separately grinding fractions of the epicarp, endocarp and seeds of the immature, mature and ripe Carica papaya fruit and filtering them through guaze. Sensitivity tests were conducted by adding 0.06 ml. of agar wells (6 mm diameter) prepared from 20 ml agar seeded with 10 cells/ml suspension of one of the eight organisms per plate. The inoculated plates were allowed to equilibrate at 4§c for one hour then incubated at 37§c for 24 hours, after which zones of inhibition were measured in millimeters. Antibacterial activity was expressed in terms of the radius of the zone of inhibition calculated as the difference in radius of the observed zones and the edge of the agar wells. Daily sensitivity tests were carried out on extracts stored at 5§c, 25§c and 35§c for 7 days. RESULTS: The seed extracts from all three stages of the fruit showed an average order of inhibition in the following order: B cereus> E coli> S faecalis> S aureus> P vulgaris> and X flexneri. There was no significant difference in bacterial sensitivity between the immature, mature and ripe fruits tested. The epicarp and endocarp did not produce any inhibition zone in any of the three stages of the fruit tested. There was a gradual reduction in antibiotic activity with increasing storage item. Also, a fall-off of activity was found to be more drastic at higher temperatures. CONCLUSION: The findings show that crude extracts of Carica papaya seed have antibacterial activity that inhibits the growth of both gram positive (B cereus, S aureus and S faecalis) and gram negative (E coli, P vulgaris and S flexneri) organisms. Observed activity was dependent on stage of maturity but tended to decrease with duration and conditions of storage. No antibacterial activity was observed from the epicarp and the endocarp of the fruit. (AU)

[The corrective action of antibodies in experimental intestinal dysbacteriosis]. / Korektiruiushchee deistvie antitel pri éksperimental'nom kishechnom disbakterioze.

As shown in this work, antisera obtained after the immunization of animals with vaccines, prepared from Salmonella minnesota strain R595 (Re mutant) or Escherichia coli O14 having enterobacterial common antigen (ECA), as well as human antisera with elevated titers of antibodies to Re glycolipid or to LPS O14 (ECA), inhibited the development of experimental intestinal dysbacteriosis in white mice, induced by the administration of ampyox in large doses. The degree of the inhibiting action of the antisera was proportional to antibody titers, which was indicative of the fact that antibodies possibly played some role in the regulation of the amount of intestinal microflora.

[The protective activity of polyclonal and monoclonal antibodies to the lipopolysaccharide of Neisseria meningitidis serogroup A in in vivo experiments]. / Protektivnaia aktivnost' poliklonal'nykh i monoklonal'nykh antitel k lipopolisakharidu Neisseria meningitidis serogruppy A v opytakh in vivo.

The protective activity of the sera of mice immunized with the preparations of native and detoxified N. meningitidis lipopolysaccharide (LPS), group A, as well as with monoclonal antibodies to N. meningitidis antigens, groups A and B, was studied on the mucin model of meningococcal infection. The study showed that the maximum level of anti-LPS antibodies in mice was observed on day 7 after the injection of LPS. Immune sera obtained from mice were capable of protecting the animals from fetal meningococcemia induced by N. meningitidis strains of homologous and heterologous groups. As shown by the results of this study, the alkaline treatment of N. meningitidis native LPS did not decrease the protective properties of antibodies. The monoclonal antibodies under study were found to possess high preventive activity in mice challenged with N. meningitidis, groups A and B. Anti-LPS monoclonal antibodies showed greater protective activity than antipolysaccharide monoclonal antibodies.