Development and preclinical evaluation of a new F(ab')2 antitoxin against botulinum neurotoxin serotype A.

Concern about the malicious applications of botulinum neurotoxin has highlighted the need for a new generation of safe and highly potent antitoxins. In this study, we developed and evaluated the preclinical pharmacology and safety of a new F(ab')2 antitoxin against botulinum neurotoxin serotype A (BoNT/A). As an alternative to formalin-inactivated toxoid, the recombinant Hc domain of botulinum neurotoxin serotype A (rAHc) was used to immunize horses, and the IgGs from the hyperimmune sera were digested to obtain F(ab')2 antitoxin. The protective effect of the new F(ab')2 antitoxin against BoNT/A was determined both in vitro and in vivo. The results showed that the F(ab')2 antitoxin could prevent botulism in mice challenged with BoNT/A and effectively delayed progression of paralysis from botulism in the therapeutic setting. The preclinical safety of the new F(ab')2 antitoxin was also evaluated, and it showed neither harmful effects on vital functions nor adverse effects such as acute toxicity, or immunological reactions in mice and dogs. Thus, our results provide valuable experimental data for this new antitoxin as a potential candidate for treatment of botulism caused by BoNT/A, and our findings support the safety of the new F(ab')2 antitoxin for clinical use. Our study further demonstrates the proof of concept for development of a similar strategy for obtaining potent antitoxin against other BoNT serotypes.

Effects of solution conditions and surface chemistry on the adsorption of three recombinant botulinum neurotoxin antigens to aluminum salt adjuvants.

Botulinum neurotoxin (BoNT) is a biological warfare threat. Protein antigens have been developed against the seven major BoNT serotypes for the development of a recombinant protein vaccine. This study is an evaluation of adsorption profiles for three of the recombinant protein antigens to aluminum salt adjuvants in the development of a trivalent vaccine against BoNT. Adsorption profiles were obtained over a range of protein concentrations. The results document that charge-charge interactions dominate the adsorption of antigen to adjuvant. Optimal conditions for adsorption were determined. However, potency studies and solution stability studies indicated the necessity of using aluminum hydroxide adjuvant at low pH. To improve the adsorption profiles to AlOH adjuvant, phosphate ions were introduced into the adsorption buffers. The resulting change in the adjuvant chemistry led to an improvement of adsorption of the BoNT antigens to aluminum hydroxide adjuvant while maintaining potency. Competitive adsorption profiles were also determined, and showed changes in maximum adsorption from mixed solutions compared to adsorption from individual protein solutions. The adsorption profiles for each protein varied due to differences in adsorption mechanism and affinity for the adjuvant surface. These results emphasize the importance of evaluating competitive adsorption in the development of multivalent vaccine products.

Formulation of botulinum neurotoxin heavy chain fragments for vaccine development: mechanisms of adsorption to an aluminum-containing adjuvant.

Heavy chain fragments of botulinum neurotoxin serotypes A and B are being developed as a bivalent vaccine for botulism. To potentiate the immune response, an aluminum containing adjuvant will be formulated with the two antigens. The adsorption mechanisms of each antigen to aluminum phosphate and aluminum hydroxide adjuvants were studied. The adsorption of the serotype A antigen to each adjuvant, and the serotype B antigen to aluminum phosphate adjuvant, is dependent on electrostatic attractive forces. The serotype A antigen is basic, and pretreatment with phosphate anions is required for favorable adsorption conditions to aluminum hydroxide adjuvant. In contrast, the serotype B antigen displays a high affinity to aluminum hydroxide adjuvant even when the two species possess the same charge. It is proposed that the serotype B antigen is adsorbed to aluminum hydroxide adjuvant by a ligand exchange mechanism.

Emerging therapeutic applications of botulinum toxin.

Botulinum toxin, the most potent known biological neurotoxin, holds great promise in the therapy of many diseases. It has been used effectively to treat strabismus, dystonias and other movement disorders, and spasticity. However, a number of potential new therapeutic indications have emerged and attracted a considerable amount of interest from the scientific community. These emerging indications included treatment for conditions associated with pain (e.g. headaches, myofascial pain, chronic low back pain), hypersecretion of glands (e.g. hyperhidrosis, sialorrhea, intrinsic rhinitis), and excessive or dyssynergic muscle contraction, and for cosmesis (e.g. myokymia, bruxism, anal fissure). There is a need for more controlled clinical trials, dose-ranging studies to determine optimal treatment, validated clinical scales and studies developed to assess the value of electromyographic guidance and skill of investigators on the outcome of treatment for some of these diseases. The long-term cost effectiveness of treatment and immunoresistance from repeated injections are also important clinical issues to address.

Antibody response to bacterial antigens covalently bound to biodegradable polymerized serum albumin beads.

Model vaccines have been made by covalently linking Clostridium botulinum type D toxin and Klebsiella pneumoniae capsular polysaccharide antigen to polymerized rabbit serum albumin beads. When injected into rabbits these bead vaccines induced an enhanced production of specific humoral antibody without causing adverse reactions. The adjuvant effect is due to a slow release from the bead structure and offers an alternative to oil emulsions and mineral salt adsorbents.