IM Recombinant Ricin Toxin Vaccine (RVEc) - 3-Dose Primary Series With Boost

Inclusion Criteria: * Study participants must read and sign an approved informed consent. * Study participants must be at least 18 years old at time of screening and no older than 50 years old at time of first study vaccination. * Participants must weigh at least 110 pounds at time of screening. * Participants must be in good health as judged from medical history, physical examination, electrocardiogram, chest x-ray, hematology, clinical chemistries, urinalysis, hepatitis serology, and human immunodeficiency virus antibody test and must be medically cleared for participation by an investigator. * Females of childbearing potential must have a negative pregnancy test on screening and the morning of each vaccination prior to receipt of the vaccine and must agree to use a highly effective method of birth control from screening through 3 months following last study vaccination. A highly effective method of birth control is defined as one with a failure rate of less than 1% per year. Acceptable birth control methods that meet this criterion include hormonal implants and injectables, combined oral contraceptives, intrauterine devices (IUDs), female sterilization (tubal ligation), sexual abstinence, or a vasectomized partner. * Female participants must also agree not to breastfeed from screening through 3 months following last study vaccination. * Study participants must be willing to return for all follow-up visits. * Study participants must agree to report any adverse events (AE) that may or may not be associated with administration of the investigational product through duration of study participation. * Study participants must agree to abstain from excessive exercise (more than the usual routine) and excessive alcohol consumption (exceeds 2 drinks for males or exceeds 1 drink for females daily or binge drinking) for the duration of study participation. Exclusion Criteria: * Acute or chronic medical conditions or immunodeficiency from a medical condition or medical treatment, medications, or dietary supplements that, in the investigator's opinion, would impair the subject's ability to respond to vaccination. Use of corticosteroids, other than inhaled or topical corticosteroids or eye drops, will not be permitted. * Severe hypersensitivity to any vaccine. * History of asthma, chronic obstructive pulmonary disease, or other current/residual diseases of the lungs. * Clinically significant abnormal laboratory tests. * Current smoker, to include use of electronic cigarettes.. * Any known allergies to sodium succinate, Polysorbate 20 (a detergent), Alhydrogel, or kanamycin. * Receipt of any vaccine or investigational product within 30 days before or after vaccination with RVEc (the only exception is the inactivated influenza vaccine that can be received at least 30 days after RVEc Dose 3 or 4). * Receipt of RVEc is contraindicated based on shoulder injury related to vaccine administration (SIRVA) checklist/screening, as determined by principle investigator. (For this Phase 1 study, we will not administer product to subjects with bilateral shoulder injuries.) * Creatine phosphokinase levels that are consistently elevated more than 2 × normal * Previous vaccination with RVEc or any other ricin vaccine candidate by any route.