Inclusion Criteria

• Each patient must have an identical twin in a normal state of health with a normal screening lab panel and a normal immune profile who is documented to be antibody and culture and polymerase chain reaction (PCR) negative for HIV.
• Ability to provide informed consent.

Exclusion Criteria

Co-existing Condition:

Patients with the following conditions or symptoms are excluded:

• Malignancy other than Kaposi's sarcoma.

Patients with the following are excluded:

• Unwillingness to comply with current NIH Clinical Center guidelines concerning appropriate notification of all current sexual partners of an individual regarding his or her positive HIV serostatus and the risk of transmission of HIV infection.
• Presence of a serious opportunistic infection or other illness or condition that, in the opinion of the principal investigator, warrants exclusion from participation in the study.

Current use of illicit drugs or significant amounts of alcohol that, in the opinion of the principal investigator, would interfere with compliance with the study.