Marked enhancement of the immune response to BioThrax® (Anthrax Vaccine Adsorbed) by the TLR9 agonist CPG 7909 in healthy volunteers.

Immunization with BioThrax(®) (Anthrax Vaccine Adsorbed) is a safe and effective means of preventing anthrax. Animal studies have demonstrated that the addition of CpG DNA adjuvants to BioThrax can markedly increase the immunogenicity of the vaccine, increasing both serum anti-protective antigen (PA) antibody and anthrax toxin-neutralizing antibody (TNA) concentrations. The immune response to CpG-adjuvanted BioThrax in animals was not only stronger, but was also more rapid and led to higher levels of protection in spore challenge models. The B-class CpG DNA adjuvant CPG 7909, a 24-base synthetic, single-strand oligodeoxynucleotide, was evaluated for its safety profile and adjuvant properties in a Phase 1 clinical trial. A double-blind study was performed in which 69 healthy subjects, age 18-45 years, were randomized to receive three doses of either: (1) BioThrax alone, (2) 1 mg of CPG 7909 alone or (3) BioThrax plus 1 mg of CPG 7909, all given intramuscularly on study days 0, 14 and 28. Subjects were monitored for IgG to PA by ELISA and for TNA titers through study day 56 and for safety through month 6. CPG 7909 increased the antibody response by 6-8-fold at peak, and accelerated the response by 3 weeks compared to the response seen in subjects vaccinated with BioThrax alone. No serious adverse events related to study agents were reported, and the combination was considered to be reasonably well tolerated. The marked acceleration and enhancement of the immune response seen by combining BioThrax and CPG 7909 offers the potential to shorten the course of immunization and reduce the time to protection, and may be particularly useful in the setting of post-exposure prophylaxis.

Increased potency of BioThrax anthrax vaccine with the addition of the C-class CpG oligonucleotide adjuvant CPG 10109.

The inclusion of an adjuvant, in addition to the existing aluminum hydroxide, in the formulation of the licensed anthrax vaccine BioThrax may have the potential to positively modify immune responses. Some potential desirable outcomes from the inclusion of an additional adjuvant include increased immune response kinetics, increased response rates, more prolonged antibody decay rates, and the ability to use less antigen per dose or fewer doses to achieve immunity. One promising group of adjuvants that is being investigated with a variety of vaccines and which has been shown to cause many of these effects are oligonucleotides which contain unmethylated CpG motifs. The C-class oligonucleotide CPG 10109, constructed of a mixed phosphorothioate/phosphodiester backbone and containing 3 CpG motifs, was added to various dilutions of BioThrax and used in mouse and guinea pig immunogenicity studies. Anti-protective antigen (PA) IgG ELISAs and the anthrax toxin neutralization assay (TNA) were performed on serum samples from both species. Anti-PA IgG and TNA responses were approximately 10-fold higher after a single dose of undiluted or diluted BioThrax upon addition of 100 microg CPG 10109 in the mouse regardless of the route of immunization. Responses were also significantly greater in the guinea pig after receiving CpG-adjuvanted undiluted BioThrax or CpG-adjuvanted BioThrax diluted 1:5, 1:10 or 1:30 compared to those achieved with BioThrax alone. A guinea pig spore challenge study showed that a single injection of BioThrax vaccine diluted 1:10 in the presence of 25 microg CPG 10109 was as protective as undiluted BioThrax, whereas a single injection of BioThrax diluted 1:10 was not protective. Taken together with the results from the immunogenicity studies, these results suggest that a CpG adjuvant could be used to reduce the dose of active ingredient required to elicit a protective response, and could lead to improved immune response kinetics.