Safety of and Immune Response to an Adenoviral HIV Vaccine (VRC-HIVADV014-00-VP) With or Without a Plasmid HIV Vaccine (VRC-HIVDNA016-00-VP) in HIV Uninfected Adults

The worldwide HIV/AIDS epidemic may only be controlled through development of a safe and effective vaccine that will prevent HIV infection. This study will evaluate the safety and immunogenicity of an experimental adenovirus-vectored multiclade HIV vaccine, VRC-HIVADV014-00-VP, followed with either a similarly structured DNA plasmid HIV vaccine, VRC-HIVDNA016-00-VP, or a placebo. The DNA plasmids in both vaccines code for proteins from HIV subtypes A, B, and C, which together represent 90% of new HIV infections in the world. HIV uninfected volunteers will be recruited in Kenya and Rwanda. Volunteers will participate in this study for 1 year. Participants will be randomly assigned to one of four groups: * Group A participants will receive a low dose of the adenovirus-vectored vaccine or placebo at study entry. * Group B participants will receive a higher dose of the adenovirus-vectored vaccine or placebo at study entry. * Group C participants will receive the DNA plasmid vaccine or placebo at study entry and Months 1 and 2. They will receive either a low dose of the adenovirus-vectored vaccine or placebo at Month 6. * Group D participants will receive the DNA plasmid vaccine or placebo at study entry and Months 1 and 2. They will receive either a higher dose of the adenovirus-vectored vaccine or placebo at Month 6. All participants will undergo vital signs measurements before and after receiving each vaccination. Participants in Groups A and B will have 9 study visits over 12 months. A physical exam, adverse events reporting, and medical and medication history will occur at each visit. HIV testing and counseling and blood and urine collection will occur at selected visits. Participants in Groups C and D will have 17 study visits over 12 months. A physical exam, adverse events reporting, and medical and medication history will occur at each visit. HIV testing and counseling and blood and urine collection will occur at selected visits.