Study of a Human Bispecific Antibody VRC-HIVMAB0121-00-AB (CAP256J3LS) Administered Intravenously or Subcutaneously to Healthy Adults

* INCLUSION CRITERIA: A participant must meet all of the following criteria: 1. Willing and able to complete the informed consent process. 2. Able to provide proof of identity to the satisfaction of the study clinician completing the enrollment process. 3. Available for clinical follow-up through the last study visit. 4. 18 to 60 years of age. 5. In good general health without a clinically significant medical history. 6. Physical examination without clinically significant findings within the 56 days prior to enrollment. 7. Adequate venous access if assigned to an IV group or adequate abdominal subcutaneous tissue if assigned to a SC group. 8. Willing to have blood samples collected, stored indefinitely, and used for research purposes. Laboratory Criteria within 56 days prior to enrollment: 9. White blood cell count (WBC): 2,500-12,000/mm\^3. 10. WBC differential either within institutional normal range or accompanied by the Principal Investigator (PI) or designee approval, excluding absolute lymphocyte count which must not be lower than normal range. 11. Platelets: 125,000 - 400,000/mm\^3. 12. Hemoglobin within institutional normal range or is lower than normal range but does not meet Grade 1 criteria and is not clinically concerning. 13. Creatinine: \<= 1.1 x Upper Limit of Normal (ULN). 14. ALT: \<= ULN. 15. AST: \<= ULN. 16. ALP: \<= ULN. 17. Total bilirubin within institutional normal range or is outside normal range but does not meet Grade 1 criteria and is not clinically concerning 18. Direct bilirubin: \<= ULN 19. Negative HIV 1/2 Antibody/Ag test. Female-Specific Criteria: 20. Agrees to use an effective means of birth control from 21 days prior to enrollment through the duration of study participation. 21. Negative beta-HCG (human chorionic gonadotropin) pregnancy test (urine or serum) on day of enrollment for women presumed to be of reproductive potential. EXCLUSION CRITERIA: A participant will be excluded if one or more of the following conditions apply: 1. Woman who is breast-feeding or planning to become pregnant during study participation. 2. Weight \> 115 kg. 3. Any history of a severe allergic reaction with generalized urticaria, angioedema or anaphylaxis prior to enrollment that has a reasonable risk of recurrence during the study. 4. Hypertension that is not well controlled. 5. Receipt of any investigational study product within 28 days prior to enrollment. 6. Receipt of an investigational HIV vaccine or anti-HIV monoclonal antibody. 7. Receipt of any live attenuated vaccine within 28 days prior to enrollment. 8. Receipt of any vaccine within 2 weeks prior to enrollment. 9. Known history of Gilbert's syndrome. 10. Known history of kidney or liver disease. 11. Diabetes mellitus (type I or II), with the exception of a history of gestational diabetes. 12. More than 10 days of systemic immunosuppressive medications or cytotoxic medications within the 4 weeks prior to enrollment or any within 14 days prior to enrollment. 13. 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. 14. Any other chronic or clinically significant medical condition that in the opinion of the investigator would jeopardize the safety or rights of the volunteer, including but not limited to diabetes mellitus, hepatitis, asthma, infectious disease, autoimmune disease, psychiatric disorder, heart disease, cancer and clinically significant forms of drug or alcohol abuse.