INCLUSION CRITERIA:

An identical twin pair, one of whom is seropositive for HIV, the other twin seronegative, by standard ELISA, PCR, and Western blot testing.

Patients whose CD4+ count is less than 500/mm(3) at entry must have been on FDA-approved or expanded-access antiretroviral agent(s) for at least 2 months.

Patients with Kaposi's sarcoma are eligible for this study, but must not have received any systemic therapy for KS within 4 weeks prior to entry. The diagnosis of KS must have been confirmed by biopsy.

Anticipated survival greater than 6 months and Karnofsky Performance Status greater than or equal to 60%.

Males or females 18 years of age or older. Every effort will be made to include both genders.

Free from serious psychological or emotional illness and able to provide written informed consent.

EXCLUSION CRITERIA - RECIPIENT:

Lymphoma.

Unwillingness to comply with current NIH Clinical Center guidelines concerning appropriate notification of all current sexual partners of an individual regarding his or her HIV positive sero-status and the risk of transmission of HIV infection.

Recent history of substance abuse unless evidence is provided of an ongoing therapeutic intervention (i.e. medical therapy or counseling) to control such abuse.

Pregnancy at entry or unwillingness to practice barrier birth control or abstinence during the study.

EXCLUSION CRITERIA - DONOR:

Untreated or inadequately treated medical condition (e.g., cardiopulmonary disease, acute infection) which, in the judgement of the Principal Investigator, precludes apheresis.

Serologic positivity for Epstein Barr virus, Cytomegalovirus, Hepatitis B or Hepatitis C if and only if the recipient twin tests seronegative for the corresponding virus.