Progress toward development of an inhalation vaccine against botulinum toxin

Subunit vaccine efficacy against Botulinum neurotoxin subtypes

Botulinum neurotoxins (BoNT) are classified into 7 serotypes (A-G) based upon neutralization by serotype-specific anti-sera. Several recombinant serotype-specific subunit BoNT vaccines have been developed, including a subunit vaccine comprising the receptor binding domain (HCR) of the BoNTs. Sequencing of the genes encoding BoNTs has identified variants (subtypes) that possess up to 32% primary amino acid variation among different BoNT serotypes. Studies were conducted to characterize the ability of the HCR of BoNT/A to protect against challenge by heterologous BoNT/A subtypes (A1-A3). High dose vaccination with HCR/A subtypes A1-A4 protected mice from challenge by heterologous BoNT/A subtype A1-A3, while low dose HCR vaccination yielded partial protection to heterologous BoNT/A subtype challenge. Absolute IgG titers to HCRs correlated to the dose of HCR used for vaccination, where HCR/A1 elicited an A1 subtype-specific IgG response, which was not observed with HCR/A2 vaccination. Survival of mice challenged to heterologous BoNT/A2 following low dose HCR/A1 vaccination correlated with elevated IgG titers directed to the denatured C-terminal sub-domain of HCR/A2, while survival of mice to heterologous BoNT/A1 following low dose HCR/A2 vaccination correlated to elevated IgG titers directed to native HCRc/A1. This implies that low dose vaccinations with HCR/A subtypes elicit unique IgG responses, and provides a basis to define how the host develops a neutralizing immune response to BoNT intoxication. These results may provide a reference for the development of pan-BoNT vaccines.

Small molecule inhibitors as countermeasures for botulinum neurotoxin intoxication

Botulinum neurotoxins (BoNTs) are the most potent of known toxins and are listed as category A biothreat agents by the U.S. CDC. The BoNT-mediated proteolysis of SNARE proteins inhibits the exocytosis of acetylcholine into neuromuscular junctions, leading to life-threatening flaccid paralysis. Currently, the only therapy for BoNT intoxication (which results in the disease state botulism) includes experimental preventative antibodies and long-term supportive care. Therefore, there is an urgent need to identify and develop inhibitors that will serve as both prophylactic agents and post-exposure ‘rescue’ therapeutics. This review focuses on recent progress to discover and develop small molecule inhibitors as therapeutic countermeasures for BoNT intoxication.

Aerosol vaccines for tuberculosis: a fine line between protection and pathology

Pulmonary delivery of vaccines against airborne infection is being investigated worldwide, but there is limited effort directed at developing inhaled vaccines for tuberculosis (TB). This review addresses some of the challenges confronting vaccine development for TB and attempts to link these challenges to the promises of mucosal immunity offered by pulmonary delivery. There are several approaches working toward this goal including subunit vaccines, recombinant strains, a novel vaccine strain Mycobacterium w, and DNA vaccine approaches. While it is clear that lung-resident adaptive immunity is an attainable goal, vaccine platforms must ensure that damage to the lung is limited during both vaccination and when memory cells respond to pathogenic infection.

Extreme sensitivity of botulinum neurotoxin domains towards mild agitation

Botulinum neurotoxins (BoNTs) and their fragments are targets of therapeutic developments and are increasingly used as therapeutic, prophylactic, and research reagents. However, published data on their properties vary widely. In order to gain a better understanding of these variations, we initiated a systematic investigation of the stability parameters of catalytic light chains (Lc) as well as of cell surface binding domains (Hc) of the neurotoxin. When followed by CD spectroscopy, we noticed that the recombinant light chains of serotypes A (LcA), B, D, E, and G rapidly lost their secondary structures by mild stirring. Denaturation of LcA increased with stirring speed and temperature resulting in a catalytically inactive precipitate. Reducing agents or an anaerobic environment were ineffective in the denaturation. Under identical conditions, bovine serum albumin, ovalbumin, carboxypeptidase B, and of thermolysin, a structural and functional analogue of LcA, remained unchanged. Hc domains of serotype A, B, C, E, and F were also denatured by mild stirring. Adding the nonionic detergent Tween-20 to LcA completely prevented the denaturation. We speculate that the BoNT domains undergo surface denaturation due to rapid exposure of hydrophobic residues by mechanical agitation. This study has important implications for handling BoNT proteins used in therapeutic development.

Botulism: cause, effects, diagnosis, clinical and laboratory identification, and treatment modalities

Botulism is a neuroparalytic disease caused by neurotoxins produced by the bacteria Clostridium botulinum. Botulinum neurotoxins (BoNTs) are among the most potent naturally occurring toxins and are a category A biological threat agent. The 7 toxin serotypes of BoNTs (serotypes A-G) have different toxicities, act through 3 different intracellular protein targets, and exhibit different durations of effect. Botulism may follow ingestion of food contaminated with BoNT, from toxin production of C botulinum present in the intestine or wounds, or from inhalation of aerosolized toxin. Intoxication classically presents as an acute, symmetrical, descending flaccid paralysis. Early diagnosis is important because antitoxin therapy is most effective when administered early. Confirmatory testing of botulism with BoNT assays or C botulinum cultures is time-consuming, and may be insensitive in the diagnosis of inhalational botulism and in as many as 32% of food-borne botulism cases. Therefore, the decision to initiate botulinum antitoxin therapy is primarily based on symptoms and physical examination findings that are consistent with botulism, with support of epidemiological history and electrophysiological testing. Modern clinical practice and antitoxin treatment has reduced botulism mortality rates from approximately 60% to < or =10%. The pentavalent botulinum toxoid is an investigational product and has been used for more than 45 years in at-risk laboratory workers to protect against toxin serotypes A to E. Due to declining immunogenicity and potency of the pentavalent botulinum toxoid, novel vaccine candidates are being developed.

Botulinum Toxin in Ophthalmology

Since its introduction into clinical medicine in 1980, botulinum toxin has become a major therapeutic drug with applications valuable to many medical sub-specialties. Its use was spearheaded in ophthalmology where its potential applications have expanded to cover a broad range of visually related disorders. These include dystonic movement disorders, strabismus, nystagmus, headache syndromes such as migraine, lacrimal hypersecretion syndromes, eyelid retraction, spastic entropion, compressive optic neuropathy, and, more recently, periorbital aesthetic uses. Botulinum toxin is a potent neurotoxin that blocks the release of acetylcholine at the neuromuscular junction of cholinergic nerves. When used appropriately it will weaken the force of muscular contraction, or inhibit glandular secretion. Recovery occurs over 3 to 4 months from nerve terminal sprouting and regeneration of inactivated proteins necessary for degranualtion of acetylcholine vesicles. Complications are related to chemodenervation of adjacent muscle groups, injection technique, and immunological mechanisms.