Delayed treatment of cynomolgus macaques with a FVM04/CA45 monoclonal antibody cocktail provides complete protection against lethal Sudan virus infection.

Sudan ebolavirus (SUDV) is a member of the genus Ebolavirus (Family Filoviridae) and has caused sporadic outbreaks of Ebola disease (EBOD), or more specifically Sudan virus disease (SVD), with high mortality rates in Africa. Current vaccines and therapies that have been developed for filoviruses are almost all specific for Ebola virus (EBOV; of the species Zaire ebolavirus), and there is a current lack of therapeutics specific for SUDV. The recent SUDV outbreak in Uganda, which was distributed across multiple districts, including Kampala, a densely populated urban center, highlights the critical need for the development of novel SUDV-specific or pan-Ebola virus therapeutics. Previous work has characterized two monoclonal antibodies, FVM04 and CA45, which have neutralization capabilities against both EBOV and SUDV and have shown protective efficacy in animal challenge studies. Here, we expand upon this work, showing that treatment with a monoclonal antibody cocktail consisting of FVM04 and CA45 provides full protection against lethal SUDV infection in cynomolgus macaques. Studies that evaluate outcomes at late time points after infection, once clinical signs of illness are apparent, are vital for assessing the therapeutic efficacy of antibody therapeutics. We have shown that when treatment is initiated as late as 5 days after infection, with a second dose given on day 8, that treated groups showed few clinical signs or morbidity, with complete survival. This work provides further evidence that FVM04 and CA45 have strong therapeutic potential against SUDV and their development as a pan-Ebola virus therapeutic should be pursued. IMPORTANCE: There are currently no approved vaccines or therapeutics for Sudan virus, a filovirus which is highly related to Ebola virus and causes similar disease and outbreaks. In this study, a cocktail of two potent monoclonal antibodies that effectively neutralize Sudan virus was tested in a nonhuman primate model of Sudan virus disease. Treatment was highly effective, even when initiated as late as 5 days after infection, when clinical signs of infection were already evident. All treated animals showed complete recovery from infection, with little evidence of disease, while all animals that received a control treatment succumbed to infection within 8 days. The study further demonstrated the strong therapeutic potential of the antibody treatment and supported further development for use in Sudan virus outbreaks.

Efficacy of Ebola Glycoprotein-Specific Equine Polyclonal Antibody Product Against Lethal Ebola Virus Infection in Guinea Pigs.

Background: Filoviruses including Ebola, Sudan, and other species are emerging zoonotic pathogens representing a significant public health concern with high outbreak potential, and they remain a potential bioterrorism-related threat. We have developed a despeciated equine Ebola polyclonal antibody (E-EIG) postexposure treatment against Ebola virus (EBOV) and evaluated its efficacy in the guinea pig model of EBOV infection. Methods: Guinea pigs were infected with guinea pig-adapted EBOV (Mayinga strain) and treated with various dose levels of E-EIG (20-100 mg/kg) twice daily for 6 days starting at 24 h postinfection. The E-EIG was also assessed for neutralization activity against related filoviruses including EBOV strains Mayinga, Kikwit, and Makona and the Bundibugyo and Taï Forest ebolavirus species. Results: Treatment with E-EIG conferred 83% to 100% protection in guinea pigs. The results demonstrated a comparable neutralization activity (range, 1:512-1:896) of E-EIG against all tested strains, suggesting the potential for cross-protection with the polyclonal antibody therapeutic. Conclusions: This study showed that equine-derived polyclonal antibodies are efficacious against lethal EBOV disease in a relevant animal model. Furthermore, the studies support the utility of the equine antibody platform for the rapid production of a therapeutic product in the event of an outbreak by a filovirus or other zoonotic pathogen.

Animal-to-Human Dose Translation of ANTHRASIL for Treatment of Inhalational Anthrax in Healthy Adults, Obese Adults, and Pediatric Subjects.

Anthrax Immune Globulin Intravenous (AIGIV [ANTHRASIL]), was developed for the treatment of toxemia associated with inhalational anthrax. It is a plasma product collected from individuals vaccinated with anthrax vaccine and contains antitoxin IgG antibodies against Bacillus anthracis protective antigen. A pharmacokinetic (PK) and exposure-response model was constructed to assess the PKs of AIGIV in anthrax-free and anthrax-exposed rabbits, non-human primates and anthrax-free humans, as well as the relationship between AIGIV exposure and survival from anthrax, based on available preclinical/clinical studies. The potential effect of anthrax on the PKs of AIGIV was evaluated and estimates of survival odds following administration of AIGIV protective doses with and without antibiotic co-treatment were established. As the developed PK model can simulate exposure of AIGIV in any species for any dosing scenario, the relationship between the predicted area under the concentration curve of AIGIV in humans and the probability of survival observed in preclinical studies was explored. Based on the simulation results, the intravenous administration of 420 U (units of potency as measured by validated Toxin Neutralization Assay) of AIGIV is expected to result in a > 80% probability of survival in more than 90% of the human population. Additional simulations suggest that exposure levels were similar in healthy and obese humans, and exposure in pediatrics is expected to be up to approximately seven-fold higher than in healthy adults, allowing for doses in pediatric populations that ranged from one to seven vials. Overall, the optimal human dose was justified based on the PK/pharmacodynamic (PD) properties of AIGIV in animals and model-based translation of PK/PD to predict human exposure and efficacy.

Treatment Efficacy of Cidofovir and Brincidofovir against Clade II Monkeypox Virus isolates.

While historically confined to endemic areas, Monkeypox virus (MPXV) infection has increasingly garnered international attention due to sporadic outbreaks in non-endemic countries in the last two decades and its potential for human-to-human transmission. In 2022, a multi-country outbreak of mpox disease was declared by the World Health Organization (WHO) and nearly 100,000 mpox cases have been reported since the beginning of this pandemic. The clade II variant of the virus appears to be responsible for the vast majority of these infections. While there are no antiviral drugs currently approved to treat mpox specifically, the use of tecovirimat (TPOXX®) and brincidofovir (Tembexa®) is recommended by the Centers for Disease Control and Prevention (CDC) for compassionate use in severe mpox cases, since both are FDA-approved for the treatment of the closely related smallpox disease. Given the emergence of multiple tecovirimat-resistant infections, we aimed to evaluate the treatment efficacy of brincidofovir and its active compound, cidofovir, against MPXV clade II strains. Following intranasal infection, we show that cidofovir and brincidofovir can strongly reduce the viral replication of MPXV clade IIa and IIb viruses in the respiratory tract of susceptible mice when administered systemically and orally, respectively. The high antiviral activity of both compounds against historical and currently circulating MPXV strains supports their therapeutic potential for clinical application.

Efficacy of ANTHRASIL (Anthrax Immune Globulin Intravenous (Human)) in rabbit and nonhuman primate models of inhalational anthrax: Data supporting approval under animal rule.

To meet the requirements of the Animal Rule, the efficacy of monotherapy with ANTHRASIL® (Anthrax Immune Globulin Intravenous (Human)) for inhalational anthrax was evaluated in blinded studies using rabbit and nonhuman primate models. Animals in both studies were randomized to treatment groups exposed to ~ 200 LD50 Bacillus anthracis (Ames strain) spores by the aerosol route to induce inhalational anthrax. Rabbits (N = 50/group) were treated with either 15 U/kg ANTHRASIL or a volume-matching dose of IGIV after disease onset as determined by the detection of bacterial toxin in the blood. At the end of the study, survival rates were 2% (1 of 48) in the IGIV control group, and 26% (13 of 50) in the ANTHRASIL-treated group (p = 0.0009). Similarly, ANTHRASIL was effective in cynomolgus monkeys (N = 16/group) when administered therapeutically after the onset of toxemia, with 6% survival in the IGIV control and a dose-related increase in survival of 36%, 43%, and 70% with 7.5, 15 or 30 U/kg doses of ANTHRASIL, respectively. These studies formed the basis for approval of ANTHRASIL by FDA under the Animal Rule.

Equine Polyclonal Antibodies Prevent Acute Chikungunya Virus Infection in Mice.

Chikungunya virus (CHIKV) is a mosquito-transmitted pathogen that causes chikungunya disease (CHIK); the disease is characterized by fever, muscle ache, rash, and arthralgia. This arthralgia can be debilitating and long-lasting, seriously impacting quality of life for years. Currently, there is no specific therapy available for CHIKV infection. We have developed a despeciated equine polyclonal antibody (CHIKV-EIG) treatment against CHIKV and evaluated its protective efficacy in mouse models of CHIKV infection. In immunocompromised (IFNAR-/-) mice infected with CHIKV, daily treatment for five consecutive days with CHIKV-EIG administered at 100 mg/kg starting on the day of infection prevented mortality, reduced viremia, and improved clinical condition as measured by body weight loss. These beneficial effects were seen even when treatment was delayed to 1 day after infection. In immunocompetent mice, CHIKV-EIG treatment reduced virus induced arthritis (including footpad swelling), arthralgia-associated cytokines, viremia, and tissue virus loads in a dose-dependent fashion. Collectively, these results suggest that CHIKV-EIG is effective at preventing CHIK and could be a viable candidate for further development as a treatment for human disease.

Passive immunotherapies protect WRvFire and IHD-J-Luc vaccinia virus-infected mice from lethality by reducing viral loads in the upper respiratory tract and internal organs.

Whole-body bioimaging was employed to study the effects of passive immunotherapies on lethality and viral dissemination in BALB/c mice challenged with recombinant vaccinia viruses expressing luciferase. WRvFire and IHD-J-Luc vaccinia viruses induced lethality with similar times to death following intranasal infection, but WRvFire replicated at higher levels than IHD-J-Luc in the upper and lower respiratory tracts. Three types of therapies were tested: licensed human anti-vaccinia virus immunoglobulin intravenous (VIGIV); recombinant anti-vaccinia virus immunoglobulin (rVIG; Symphogen, Denmark), an investigational product containing a mixture of 26 human monoclonal antibodies (HuMAbs) against mature virion (MV) and enveloped virion (EV); and HuMAb compositions targeting subsets of MV or EV proteins. Bioluminescence recorded daily showed that pretreatment with VIGIV (30 mg) or with rVIG (100 µg) on day -2 protected mice from death but did not prevent viral replication at the site of inoculation and dissemination to internal organs. Compositions containing HuMAbs against MV or EV proteins were protective in both infection models at 100 µg per animal, but at 30 µg, only anti-EV antibodies conferred protection. Importantly, the t statistic of the mean total fluxes revealed that viral loads in surviving mice were significantly reduced in at least 3 sites for 3 consecutive days (days 3 to 5) postchallenge, while significant reduction for 1 or 2 days in any individual site did not confer protection. Our data suggest that reduction of viral replication at multiple sites, including respiratory tract, spleen, and liver, as monitored by whole-body bioluminescence can be used to predict the effectiveness of passive immunotherapies in mouse models.

Evaluation of therapeutic interventions for vaccinia virus keratitis.

BACKGROUND: Vaccinia virus keratitis (VACVK) is a complication of smallpox vaccination that can result in blindness. There are no Food and Drug Administration-approved treatments for VACVK, and vaccinia immunoglobulin (VIG) is contraindicated in isolated VACVK. We used a rabbit model of infection to compare several therapeutic options for VACVK. METHODS: Rabbit eyes were infected with 10(5) plaque-forming units of the Dryvax strain of vaccinia virus and scored daily for 28 days using a modified MacDonald-Shadduck scoring system. Animals were treated for 10 days after the onset of keratitis with albumin, VIG, prednisolone acetate, trifluridine, or combinations thereof. Ocular viral titers and vaccinia-specific antibody titers were determined by plaque assay and enzyme-linked immunosorbent assay, respectively. RESULTS: Treatment with intravenous VIG neither exacerbated nor ameliorated VACVK. Topical prednisolone acetate interfered with viral clearance, and ocular disease rebounded in prednisolone-treated groups. The most effective treatment was topical trifluridine alone. CONCLUSIONS: We conclude that (1) VIG did not negatively affect the treatment of isolated keratitis, (2) topical corticosteroids should not be used for treating VACVK, and (3) treatment with topical trifluridine, with or without intravenous VIG, is the preferred therapeutic regimen for treating VACVK.

Pharmacokinetic and Pharmacodynamic Effects of Polyclonal Antibodies against SARS-CoV2 in Mice.

Despite ongoing vaccination efforts to prevent SARS-CoV-2 infections, treatment tools are still necessary to address the ongoing COVID-19 pandemic. We report here that COVID-HIGIV, a human immunoglobulin product for treatment of COVID-19, provided a significant survival benefit in SARS-CoV-2 infected transgenic mice compared to controls. COVID-HIGIV also has similar pharmacokinetic profiles in healthy and SARS-CoV-2 infected mice over time after intravenous administration, with identical or comparable Tmax, Cmax, AUC0-∞ and Cl. AUC0-last increased and mean residence time, T1/2, and Vd reduced in infected animals compared to healthy animals. These data suggest that COVID-HIGIV may be an effective treatment for SARS-CoV-2 infection when given early after exposure.

Exposure-Response Modeling and Simulation to Support Human Dosing of Botulism Antitoxin Heptavalent Product.

Botulism antitoxin heptavalent (A, B, C, D, E, F, and G - Equine; BAT) product is a sterile solution of F(ab')2 and F(ab')2 -related antibody fragments prepared from plasma obtained from horses that have been immunized with a specific serotype of botulinum toxoid and toxin. BAT product is indicated for the treatment of symptomatic botulism following documented or suspected exposure to botulinum neurotoxin serotypes A to G in adults and pediatric patients. Pharmacokinetic and exposure-response models were used to explore the relationship between BAT product exposure and the probability of survival, and the occurrence of relevant moderate clinical signs observed during the preclinical development of BAT product to justify the clinical dose. The predicted probability of survival in humans for all serotypes of botulinum neurotoxin was more than 95.9% following intravenous administration of one vial of BAT product. Furthermore, this BAT product dose is expected to result in significant protection against clinical signs in human adults for all botulinum neurotoxin serotypes. Our exposure response model indicates that we have sufficient antitoxin levels to give full protection at various theoretical exposure levels and, based on neutralization capacity/potency of one dose of BAT product, it is expected to exceed the amount of circulating botulinum neurotoxin.

Efficacy of COVID-HIGIV in animal models of SARS-CoV-2 infection.

In late 2019 the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus emerged in China and quickly spread into a worldwide pandemic. It has caused millions of hospitalizations and deaths, despite the use of COVID-19 vaccines. Convalescent plasma and monoclonal antibodies emerged as major therapeutic options for treatment of COVID-19. We have developed an anti-SARS-CoV-2 immunoglobulin intravenous (Human) (COVID-HIGIV), a potential improvement from using convalescent plasma. In this report the efficacy of COVID-HIGIV was evaluated in hamster and mouse models of SARS-CoV-2 infection. COVID-HIGIV treatment in both mice and hamsters significantly reduced the viral load in the lungs. Among COVID-HIGIV treated animals, infection-related body weight loss was reduced and the animals regained their baseline body weight faster than the PBS controls. In hamsters, COVID-HIGIV treatment reduced infection-associated lung pathology including lung inflammation, and pneumocyte hypertrophy in the lungs. These results support ongoing trials for outpatient treatment with COVID-HIGIV for safety and efficacy evaluation (NCT04910269, NCT04546581).

Human immune globulin treatment controls Zika viremia in pregnant rhesus macaques.

There are currently no approved drugs to treat Zika virus (ZIKV) infection during pregnancy. Hyperimmune globulin products such as VARIZIG and WinRho are FDA-approved to treat conditions during pregnancy such as Varicella Zoster virus infection and Rh-incompatibility. We administered ZIKV-specific human immune globulin as a treatment in pregnant rhesus macaques one day after subcutaneous ZIKV infection. All animals controlled ZIKV viremia following the treatment and generated robust levels of anti-Zika virus antibodies in their blood. No adverse fetal or infant outcomes were identified in the treated animals, yet the placebo control treated animals also did not have signs related to congenital Zika syndrome (CZS). Human immune globulin may be a viable prophylaxis and treatment option for ZIKV infection during pregnancy, however, more studies are required to fully assess the impact of this treatment to prevent CZS.

The Ability of Zika virus Intravenous Immunoglobulin to Protect From or Enhance Zika Virus Disease.

The closely related flaviviruses, dengue and Zika, cause significant human disease throughout the world. While cross-reactive antibodies have been demonstrated to have the capacity to potentiate disease or mediate protection during flavivirus infection, the mechanisms responsible for this dichotomy are still poorly understood. To understand how the human polyclonal antibody response can protect against, and potentiate the disease in the context of dengue and Zika virus infection we used intravenous hyperimmunoglobulin (IVIG) preparations in a mouse model of the disease. Three IVIGs (ZIKV-IG, Control-Ig and Gamunex®) were evaluated for their ability to neutralize and/or enhance Zika, dengue 2 and 3 viruses in vitro. The balance between virus neutralization and enhancement provided by the in vitro neutralization data was used to predict the IVIG concentrations which could protect or enhance Zika, and dengue 2 disease in vivo. Using this approach, we were able to define the unique in vivo dynamics of complex polyclonal antibodies, allowing for both enhancement and protection from flavivirus infection. Our results provide a novel understanding of how polyclonal antibodies interact with viruses with implications for the use of polyclonal antibody therapeutics and the development and evaluation of the next generation flavivirus vaccines.

Application of bioluminescence imaging to the prediction of lethality in vaccinia virus-infected mice.

To find an alternative endpoint for the efficacy of antismallpox treatments, bioluminescence was measured in live BALB/c mice following lethal challenge with a recombinant WR vaccinia virus expressing luciferase. Intravenous vaccinia immunoglobulin treatments were used to confer protection on a proportion of animals. Using known lethality outcomes in 200 animals and total fluxes recorded daily in live animals, we performed univariate receiver operating characteristic (ROC) curve analysis to assess whether lethality can be predicted based on bioluminescence. Total fluxes in the spleens on day 3 and in the livers on day 5 generated accurate predictive models; the area under the ROC curve (AUC) was 0.91. Multiple logistic regression analysis utilizing a linear combination of six measurements: total flux in the liver on days 2, 3, and 5; in the spleen on days 1 and 3; and in the nasal cavity on day 4 generated the most accurate predictions (AUC = 0.96). This model predicted lethality in 90% of animals with only 10% of nonsurviving animals incorrectly predicted to survive. Compared with bioluminescence, ROC analysis with 25% and 30% weight loss as thresholds accurately predicted survival on day 5, but lethality predictions were low until day 9. Collectively, our data support the use of bioimaging for lethality prediction following vaccinia virus challenge and for gaining insight into protective mechanisms conferred by vaccines and therapeutics.

Efficacy of anti-influenza immunoglobulin (FLU-IGIV) in ferrets and mice infected with 2009 pandemic influenza virus.

Seasonal influenza causes significant morbidity and mortality around the world each year, even with the use of vaccines and antivirals. There is a need for more effective treatments for severe and hospitalized cases of influenza. In this study, we have tested the efficacy of a human plasma-derived IgG product (FLU-IGIV) against seasonal influenza in mouse and ferret models of influenza infection. FLU-IGIV successfully protected mice (100% survival) against lethal influenza infection. Also, the survival rate observed with FLU-IGIV treatment was better than the survival rate observed with oseltamivir (60% survival). FLU-IGIV significantly reduced the viral load in the lungs compared to placebo (PBS) in ferrets infected with influenza A/California/07/2009 (H1N1pdm09) virus. Overall, these studies demonstrate the efficacy of human plasma-derived FLU-IGIV in relevant animal models of influenza virus infection.

Therapeutic efficacy of equine botulism heptavalent antitoxin against all seven botulinum neurotoxins in symptomatic guinea pigs.

Botulism neurotoxins are highly toxic and are potential agents for bioterrorism. The development of effective therapy is essential to counter the possible use of these toxins in military and bioterrorism scenarios, and to provide treatment in cases of natural intoxication. Guinea pigs were intoxicated with a lethal dose of botulinum neurotoxin serotypes A, B, C, D, E, F or G, and at onset of the clinical disease intoxicated animals were treated with either BAT® [Botulism Antitoxin Heptavalent (A, B, C, D, E, F, G)-(Equine)] or placebo. BAT product treatment significantly (p<0.0001) enhanced survival compared to placebo for all botulinum neurotoxin serotypes and arrested or mitigated the progression of clinical signs of botulism intoxication. These results demonstrated the therapeutic efficacy of BAT product in guinea pigs and provided supporting evidence of effectiveness for licensure of BAT product under FDA 21 CFR Part 601 (Subpart H Animal Rule) as a therapeutic for botulism intoxication to serotypes A, B, C, D, E, F or G in adults and pediatric patients.

Efficacy of equine botulism antitoxin in botulism poisoning in a guinea pig model.

BACKGROUND: Botulism is a disease caused by neurogenic toxins that block acetylcholine release, resulting in potentially life threatening neuroparalysis. Seven distinct serotypes of botulinum neurotoxins (BoNTs) have been described and are found in nature world-wide. This, combined with ease of production, make BoNTs a significant bioweapon threat. An essential countermeasure to this threat is an antitoxin to remove circulating toxin. An antitoxin, tradename BAT (Botulism Antitoxin Heptavalent (A, B, C, D, E, F, G)-(Equine)), has been developed and its efficacy evaluated against all seven serotypes in guinea pigs. METHODS AND FINDINGS: Studies were conducted to establish the lethal dose and clinical course of intoxication for all seven toxins, and post-exposure prophylactic efficacy of BAT product. Animals were monitored for signs of intoxication and mortality for 14 days. Guinea pig intramuscular LD50s (GPIMLD50) for all BoNTs ranged from 2.0 (serotype C) to 73.2 (serotype E) of mouse intraperitoneal LD50 units. A dose of 4x GPIMLD50 was identified as the appropriate toxin dose for use in subsequent efficacy and post-exposure prophylaxis studies. The main clinical signs observed included hind limb paralysis, weak limb, change in breathing rate/pattern, and forced abdominal respiration. Mean time to onset of clinical signs ranged from 12 hours (serotype E) to 39 hours (serotype G). Twelve hours post-intoxication was selected as the appropriate time point for intervention for all serotypes apart from E where 6 hours was selected because of the rapid onset and progression of clinical signs. Post-exposure treatment with BAT product resulted in a significantly (p<0.0001) higher survival at >0.008 scaled human dose for serotypes A, B, C, F and G, at >0.2x for serotype D and >0.04x for serotype E. CONCLUSIONS: These studies confirm the efficacy of BAT as a post-exposure prophylactic therapy against all seven known BoNT serotypes.

Human Polyclonal Antibodies Prevent Lethal Zika Virus Infection in Mice.

Zika virus (ZIKV) is an emerging mosquito-borne flavivirus that represents a major threat to global health. ZIKV infections in adults are generally asymptomatic or present with mild symptoms. However, recent outbreaks of ZIKV have revealed that it can cause Congenital Zika Syndrome in neonates and Guillain-Barré syndrome in adults. Currently, no ZIKV-specific vaccines or antiviral treatments are available. In this study, we tested the efficacy of convalescent plasma IgG hyperimmune product (ZIKV-IG) isolated from individuals with high neutralizing anti-ZIKV titers as a therapeutic candidate against ZIKV infection using a model of ZIKV infection in Ifnar1-/- mice. ZIKV-IG successfully protected mice from lethal ZIKV challenge. In particular, ZIKV-IG treatment at 24 hours after lethal ZIKV infection improved survival by reducing weight loss and tissue viral burden and improving clinical score. Additionally, ZIKV-IG eliminated ZIKV-induced tissue damage and inflammation in the brain and liver. These results indicate that ZIKV-IG is efficacious against ZIKV, suggesting this human polyclonal antibody is a viable candidate for further development as a treatment against human ZIKV infection.

Preparation and characterization of monopegylated human granulocyte-macrophage colony-stimulating factor.

ABSTRACT Conjugates of recombinant human granulocyte-macrophage colony-stimulating factor (GM-CSF) attached to polyethylene glycol (PEG) chains were prepared using amine-reactive chemistry. Molecular masses of the PEGs were 20, 30, and 40 kDa. The monopegylated forms were isolated by anion-exchange chromatography and characterized by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), size-exclusion chromatography, mass spectrometry, reverse-phase high-performance liquid chromatography (HPLC), peptide mapping, in vitro cell proliferation bioassays, and rat pharmacokinetic studies. The pegylation site of the purified monopegylated products was identified as the N-terminus of the protein. All forms of pegylated GM-CSF were able to stimulate TF-1 cell proliferation in a colorimetric bioassay at concentrations equal to or lower than that of GM-CSF. Pharmacokinetic studies in rats demonstrated 32-fold, 27-fold, and 40-fold extensions in elimination half-lives for 20, 30, and 40 kDa PEG-GM-CSF, respectively, as compared with nonmodified GM-CSF.

Therapeutic efficacy of equine botulism antitoxin in Rhesus macaques.

BACKGROUND: There are currently no licensed vaccines available for prevention of botulism in humans. The vaccination is not desirable due to expanding therapeutic indications of botulinum toxins. The only available specific treatment for botulism is antitoxin to remove circulating toxin, thus, preventing further neuronal damage. BAT® (Botulism Antitoxin Heptavalent (A, B, C, D, E, F, G)-(Equine)) has been developed and its therapeutic efficacy evaluated against botulinum neurotoxin serotype A (BoNT/A) in Rhesus macaques. METHODS AND FINDINGS: In a post-exposure prophylaxis (PEP) study, animals were exposed to 4x LD50/kg of BoNT/A and administered intravenously with either BAT (1x or 0.1x scaled human dose), or placebo at 4 hours post-exposure. The animals were monitored for 14 days. For the therapeutic intervention studies, animals were exposed to a 1.7x LD50/kg of BoNT/A and treated intravenously with either placebo or BAT at a 1x scaled human dose at the onset of clinical signs. Animals were monitored on an hourly basis for 14 or 21 days. In the PEP study, all animals tolerated equine based antitoxin without any adverse clinical signs. A 100% survival was observed in groups treated with the BAT compared to 0% survival in those treated with the placebo (p<0.001, Fisher's exact test). BAT antitoxin prevented the development of signs of neurotoxicity of botulinum toxin. In a therapeutic study, treatment with the BAT at scaled 1x human dose after the onset of clinical signs significantly enhanced survival compared to the placebo (46.6% vs. 0%, p<0.0001, Fisher's exact test). Additionally, treatment with the BAT delayed the progression of signs (muscular weakness, respiratory distress, oral/nasal discharge) of toxin intoxication and reduced the severity of the disease. CONCLUSIONS: A single dose of BAT, when administered to symptomatic monkeys, resulted in a statistically significant survival benefit compared to the placebo. Additionally, BAT completely protected monkeys from the clinical signs of intoxication and subsequent death when administered as PEP treatment. These data in part supported the licensure of BAT under the Animal Rule in the United States by the Food and Drug Administration.