This study will test the safety and effectiveness of genetically altered T lymphocytes (white blood cells of the immune system) in reducing viral load in patients infected with the human immunodeficiency virus (HIV). The lymphocytes will have two genes inserted into them; a laboratory-manufactured anti-HIV gene designed to inhibit HIV reproduction (either the RevTD or Rev-TD-antiTAR gene), and a "marker" gene that will show whether or not the inserted genes have gotten into the cells.

Identical twin pairs 18 years of age and older- one of whom is HIV-positive (infected with the human immunodeficiency virus) and the other HIV-negative (not infected) may be eligible for this study.

All participants will have a complete medical history and physical examination, blood tests and a tetanus booster shot, if indicated. The non HIV-infected twin will then undergo lymphapheresis to collect lymphocytes. In this procedure, whole blood is collected through a needle placed in an arm vein. The blood circulates through a machine that separates it into its components. The lymphocytes are then removed, and the red cells and plasma are returned to the donor, either through the same needle or through a second needle placed in the other arm.

The donor cells are grown in the laboratory for a few days, and then the new genes are inserted into them. The genetically altered cells are grown in the laboratory for several days until their numbers increase approximately a thousand-fold. They are then infused intravenously (through a vein) into the infected twin. These procedures-lymphapheresis, gene modification and infusion-will be repeated at approximately 2-month intervals up to four times.

Each lymphocyte infusion takes about 60 minutes. The patient's vital signs (temperature, pulse, blood pressure and breathing) are monitored frequently during the infusion and hourly for 4 hours after the infusion. Blood samples are taken the day of the infusion, 3 days later, and then weekly to monitor the gene-modified cells, immune status, viral activity, and other factors. These tests may be done less often as the study progresses and more is learned about the safety of the infusions. The infusions are done on an outpatient basis unless side effects require that they be done in the hospital with post-infusion monitoring for at least 24 hours.

Patients will be followed for long-term effects of treatment monthly for the first 3 months, once a month for the next 9 months and yearly from then on.

This study will contribute information about the use and side effects of gene therapy in HIV infection that may lead to new treatment strategies.

A potential direct benefit to HIV-infected individuals participating in this study is reduced viral load; in laboratory studies, the RevTD and Rev-TD-antiTAR genes have inhibited HIV spread in the test tube. However, this is an early phase of study, and the likelihood of receiving this benefit is unknown.