HIV-1 Vaccine Booster in Previously Immunized Uninfected Adult Volunteers

* INCLUSION CRITERIA: A participant must meet all of the following criteria: Completed three injections of 4 mg or 8 mg of study vaccine in VRC 004 (03-I-0022) without experiencing a serious adverse event (SAE) that was possibly, probably or definitely related to study vaccine. Available for clinical follow-up for 24 weeks after enrollment. Completion of an Assessment of Understanding prior to enrollment and able to verbalize understanding of all questions answered incorrectly. Able and willing to complete the informed consent process. Willing to receive HIV test results and willing to abide by NIH guidelines for partner notification of positive HIV results. Willing to donate blood for sample storage to be used for future research. Willing to discuss HIV infection risks and amenable to risk reduction counseling. In good general health without clinically significant medical history and satisfactory completion of the screening process. Laboratory Criteria within 28 days prior to enrollment: Hemoglobin greater than or equal to 11.5 g/dL for women; greater than or equal to 13.5 g/dL for men. WBC = 3,300-12,000 cells/mm(3). Differential either within institutional normal range or accompanied by site physician approval. Total lymphocyte count greater than or equal to 800 cells/mm(3). Platelets = 125,000 - 550,000/mm(3). ALT (SGPT) less than or equal to 1.25 x upper limit of normal. Serum creatinine less than or equal to 1 x upper limit of normal (less than or equal to 1.3 mg/dL for females; less than or equal to 1.4 mg/dL for males). Normal urinalysis defined as negative glucose, negative or trace protein, and no clinically significant blood in the urine. Negative HIV PCR. Negative Hepatitis B surface antigen. Negative anti-HCV. Female-Specific Criteria: Negative beta-HCG pregnancy test (urine) on day of study enrollment for women presumed to be of reproductive potential. A female participant must meet one of the following criteria: No reproductive potential because of menopause \[one year without menses\] or because of a hysterectomy, bilateral oophorectomy, or tubal ligation, or Participant agrees to be heterosexually inactive at least 21 days prior to enrollment and through Week 24 of the study, or Participant agrees to consistently practice contraception at least 21 days prior to enrollment and through Week 24 of the study by one of the following methods: * condoms, male or female, with or without a spermicide * diaphragm or cervical cap with spermicide * intrauterine device * contraceptive pills or patch, Norplant, Depo-Provera or other FDA-approved contraceptive method * male partner has previously undergone a vasectomy for which there is documentation. EXCLUSION CRITERIA: A volunteer will be excluded if one or more of the following conditions apply: Women: Breast-feeding or planning to become pregnant during the 24 weeks of study participation. Volunteer has received any of the following substances: Immunosuppressive or cytotoxic medications or inhaled corticosteroids within the past six months (with the exception of corticosteroid nasal spray for allergic rhinitis or topical corticosteroids for an acute uncomplicated dermatitis). Blood products within 120 days prior to HIV screening. Immunoglobulin within 60 days prior to HIV screening. Live attenuated vaccines within 30 days prior to initial study vaccine administration. Investigational research agents within 30 days prior to study vaccine administration. Medically indicated subunit or killed vaccines, e.g. influenza, pneumococcal, or allergy treatment with antigen injections, within 14 days of study vaccine administration. Current anti-TB prophylaxis or therapy. Volunteer has a history of any of the following clinically significant conditions: Serious adverse reactions to vaccines such as anaphylaxis, hives, respiratory difficulty, angioedema, or abdominal pain. Autoimmune disease or immunodeficiency. Asthma that is unstable or required emergent care, urgent care, hospitalization or intubation during the past two years or that requires the use of oral or intravenous corticosteroids. Diabetes mellitus (type I or II), with the exception of gestational diabetes. History of thyroidectomy or thyroid disease that required medication within the past 12 months. Serious angioedema episodes within the previous 3 years or requiring medication in the previous two years. Hypertension that is not well-controlled by medication or is more than 145/95 at enrollment. Bleeding disorder diagnosed by a doctor (e.g. factor deficiency, coagulopathy, or platelet disorder requiring special precautions) or significant bruising or bleeding difficulties with IM injections or blood draws. Syphilis infection that is active or a positive serology due to a syphilis infection treated less than six months ago. Malignancy that is active or treated malignancy for which there is not reasonable assurance of sustained cure or malignancy that is likely to recur during the period of the study. Seizure disorder other than: 1) febrile seizures under the age of two, 2) seizures secondary to alcohol withdrawal more than 3 years ago, or 3) a singular seizure not requiring treatment within the last 3 years. Asplenia or any condition resulting in the absence or removal of the spleen. Psychiatric condition that precludes compliance with the protocol; past or present psychoses; past or present bipolar disorder requiring therapy that has not been well controlled on medication for the past two years; disorder requiring lithium; or suicidal ideation occurring within five years prior to enrollment. Any medical, psychiatric, social condition, occupational reason or other responsibility that, in the judgment of the investigator, is a contraindication to protocol participation or impairs a volunteer's ability to give informed consent.