A Three-Dose Intramuscular Injection Schedule of Anthrax Vaccine Adsorbed Generates Sustained Humoral and Cellular Immune Responses to Protective Antigen and Provides Long-Term Protection against Inhalation Anthrax in Rhesus Macaques

Abstract

05). PA-specific gamma interferon (IFN-␥) and interleukin-4 (IL-4) CD4؉ cell frequencies and T cell stimulation indices were sustained through 50.5 months (the last time point measured). PA-specific memory B cell frequencies were highly variable but, in general, were detectable in peripheral blood mononuclear cells (PBMC) by 2 months, were significantly above control levels by 7 months, and remained detectable in the HuAVA and 1:5 and 1:20 AVA groups through 42 months (the last time point measured). HuAVA and diluted AVA elicited a combined Th1/Th2 response and robust immunological priming, with sustained production of high-avidity PA-specific functional antibody, long-term immune cell competence, and immunological memory (30 months for 1:20 AVA and 52 months for 1:10 AVA). Vaccinated animals surviving inhalation anthrax developed high-magnitude anamnestic anti-PA IgG and TNA responses.

Humoral and Cell-Mediated Immune Responses to Alternate Booster Schedules of Anthrax Vaccine Adsorbed in Humans

“…In a rhesus macaque model of inhalation anthrax, the AVA 3-IM priming series diluted up to 1/10 with no additional boosters provided significant levels of protection (60 to 100%) for up to 4 years after the first vaccination (13). The immunological characteristics of these long-term protective responses in NHPs have been reported previously, and anti-PA IgG was identified as the most accurate immune correlate of protection (COP) (1).…”

“…Laboratory methods and statistical analyses of humoral and CMI responses in humans were by design similar or equivalent to those reported previously for the analogous responses in rhesus macaques (13). Modifications for species-specific conditions and reagents are described below.…”

“…As reported previously for analogous studies with NHPs, assays for all four IgG subclasses were run when the total anti-PA IgG was Ն5 g/ml (13). Relative subclass proportions were determined in a sample when the total anti-PA IgG was Ն12.5 g/ml, all four subclasses were evaluated, and at least one IgG subclass was detected.…”

“…Detection and quantification of each of the anti-PA IgG subclasses were done in separate assays using anti-human specific monoclonal antibodies for each of the four human IgG subclasses (mouse anti-human IgG1, Anti-PA IgG avidity. Serum samples with Ն5 g/ml of total anti-PA IgG were evaluated for avidity, an indirect assessment of polyclonal antibody affinity, immune response maturation, and a surrogate for MBC persistence (13,17). The avidity indices (AIs) were determined by anti-PA IgG elution from immobilized rPA with ammonium thiocyanate (NH 4 SCN; 0.078 to 5 M) (Sigma).…”

“…However, a COP cross-walk analysis between NHPs and humans receiving only the 3-IM priming series estimated that even the lowest levels of anti-PA IgG provided significant probability of survival in humans (86.8% to 95.8%) in a combined model for two alternate booster schedules (3). In the present COP substudy of the CDC Anthrax Vaccine Research Program (AVRP) human clinical trial, we conducted the first detailed evaluation in humans of the earliest onset, magnitude, and duration of PA-specific humoral and CMI profiles analogous to those providing long-term protection in NHPs (13). The objectives were to evaluate the potential immunological effects of route of vaccine administration and the feasibility of adopting alternate booster schedules.…”