Anthrax-rPA: Safety, Tolerability, Immunogenicity

The primary objective is to determine the tolerability and safety, from days 0 to 210, of escalating doses of rPA either with or without Alhydrogel (an adjuvant; used to increase the action of the principle drug) given in a two-dose, intramuscular regimen to health adults. The secondary objective is to evaluate antibody responses to rPA, from days 0 to 210, following one of four escalating doses of vaccine given with and without Alhydrogel given in a two-dose series to healthy adults, and to compare immune responses following rPA with those following BioThrax (tm) given by either the intramuscular or SQ route. The tertiary objective is to describe the antibody kinetics following vaccination. This information will be used to determine the most probable optimal dose of rPA and/or Alhydrogel that is safe, well tolerated, and maximally immunogenic for use in future phase II trials.