Hookworms digest hemoglobin from erythrocytes for use as an energy source via a proteolytic cascade that begins with the aspartic protease, APR-1. Vaccination with recombinant APR-1 has protected animals from infection in challenge studies. This study will evaluate the safety and immunogenicity of two formulations of Na-APR-1 (M74) in healthy adult volunteers when co-administered with different concentrations of the immunostimulant GLA-AF.