Repeat-Dose Toxicity Study of a Lyophilized Recombinant Protective Antigen-Based Anthrax Vaccine Adjuvanted With CpG 7909

Abstract

A recombinant protective antigen (rPA) anthrax vaccine candidate (rPA7909) was developed as a next-generation vaccine indicated for postexposure prophylaxis of disease resulting from suspected or confirmed Bacillus anthracis exposure. The lyophilized form of rPA7909-vaccinated candidate contains 75 µg purified rPA, 750 µg aluminum (as Alhydrogel adjuvant), and 250 µg of an immunostimulatory Toll-like receptor 9 agonist oligodeoxynucleotide CpG 7909 in a 0.5 mL phosphate-buffered suspension. General toxicity and local reactogenicity were evaluated in Sprague Dawley rats vaccinated with the full human dose of rPA7909 by intramuscular injection. Animals were immunized on study days 1, 15, and 29. Control groups were administered diluent only or adjuvant control (excipients, CpG 7909, and Alhydrogel adjuvant in diluent) intramuscularly at the same dose volume and according to the same schedule used for rPA7909. Toxicity was assessed based on the results of clinical observations, physical examinations, body weights, injection site reactogenicity, ophthalmology, clinical pathology (hematology, coagulation, and serum chemistry), organ weights, and macroscopic and microscopic pathology evaluation. The immune response to rPA7909 vaccination was confirmed by measuring serum anti-PA immunoglobulin G levels. The rPA7909 vaccine produced no apparent systemic toxicity and only transient reactogenicity at the injection site. The injection site reaction from animals receiving the adjuvant control was very similar to those receiving rPA7909 with respect to the inflammation. The inflammatory response observed in the injection site and the draining lymph nodes was consistent with expected immune stimulation. The overall results indicated a favorable safety profile for rPA7909.

Developmental and reproductive safety evaluation of AV7909 anthrax vaccine candidate in rats

“…This observation suggests that the nodules were largely resolved between 2 and 5 weeks after the last injection. Similar nodules associated with IM injection of rPA7909 and CPG 7909, consisting of microscopic inflammation of the skeletal muscle and/or subcutis, have been described previously (Savransky et al, 2019).…”

“…Animals were dosed 14 days prior to start of cohabitation (Study Day [SD] 1), on the day of cohabitation (SD 15), and on gestation day (GD) 7. Administration of two doses 2 weeks apart during the premating period was based on a previous study in rats (Savransky et al, 2019). The additional dose on GD 7 was included to ensure high antibody titers and provide exposure to the test article during organogenesis.…”

“…The nonclinical safety and efficacy of anthrax vaccines has been demonstrated in several animal studies (Ionin et al, 2013; Savransky et al, 2017). Vaccination with rPA7909, a recombinant protective antigen anthrax vaccine candidate adjuvanted with CPG 7909, produced robust immune activation in adult rodents with no systemic toxicity observed after the full human dose of vaccine was administered (Savransky, Lacy, Ionin, Skiadopoulos, & Shearer, 2019). BioThrax vaccination of female rabbits twice prior to mating and once during gestation did not produce any reproductive or developmental toxicity while generating a robust immune response and antibody transfer to fetuses and pups (Franco, Lewis, Morseth, Simon, & Waytes, 2009).…”

Repeat Dose Toxicity Study of the AV7909 Anthrax Vaccine Candidate in Juvenile Rats

“…12 Rats also respond well to CPG 7909 ODN as a vaccine adjuvant component. 6 The study was conducted under Good Laboratory Practices 13 . The housing and animal care practices met current standards of Association for Assessment and Accreditation of Laboratory Animal Care, and current requirements stated in the Guide for the Care and Use of Laboratory Animals 14 and Animal Welfare Act regulations.…”

“…5 Vaccination of rats with rPA7909, a vaccine candidate based on the recombinant PA protein (rather than the native PA such as that contained in the culture filtrates used to manufacture AVA), which is also adjuvanted with CPG 7909, produced robust immune stimulation with no systemic toxicity. 6 Clinical safety of AV7909 was subsequently demonstrated in several clinical studies, which showed that AV7909 vaccination was not associated with an increase in adverse events as compared to AVA, with the most common events being injection site reactions. 2,7,8 Young animals are considered appropriate models for pediatric assessments.…”