Some persons infected with the AIDS virus develop a condition known as AlDS-related complex, or ARC, characterized by fatigue, fever, weight loss, diarrhea, and swollen lymph glands. Yet other persons who are infected with the AIDS virus apparently remain well; however, even though they develop no symptoms, they can transmit the virus to others.

AIDS is a contagious disease, spread by intimate sexual contact, by direct inoculation of the virus into the bloodstream or from mother to child during pregnancy. Most of the AIDS cases in the United States have been found among homosexual and bisexual men with multiple sex partners, and among intravenous drug abusers. Others have involved men who received untreated blood products for hemophilia; persons who received transfusions of inadvertently contaminated blood-primarily before the AIDS virus was discovered and virtually eliminated from the nation's blood supply with a screening test; the heterosexual partners of persons with AIDS, and children born to infected mothers.

There is presently no cure for AIDS, although several drugs have been developed that appear to hold the virus in check, at least for a time. AIDS patients are also being treated with agents, such as interleukin-2, that bolster immune responses. Bone marrow transplants between identical twins, one with AIDS and the other healthy have brought temporary respite in experimental studies. Research on a vaccine to prevent the spread of AIDS is under way

 Bone Marrow Transplants

When the immune response is severely depressed-as the result of inherited defects, cancer therapy or AIDS-one possible remedy is a transfer of healthy bone marrow. Bone marrow transplants are also used to treat patients with cancers of the blood, the blood-forming organs, and the lymphoid system-the leukemias and lymphomas.

Once in the circulation, transplanted bone marrow cells travel to the bones where the immature cells grow into functioning B and T cells. Like other transplanted tissue, however, bone marrow from a donor must carry self markers that closely match those of the person intended to receive it. This match is essential not only to prevent the transplant from being rejected, but also to fend off a life-threatening situation known as graft-versus-host disease. In graft-versus-host disease, mature T cells from the donor attack and destroy the tissues of the recipient.

To prevent graft-versus-host disease, scientists have developed techniques to. "cleanse" the donor marrow of potentially dangerous mature T cells. These include chemicals and, more recently, a monoclonal antibody (OKT3) that specifically recognizes and eliminates mature T cells.

For cancer patients who face immunosuppressive therapy, but who have no readily matched donor, doctors have used "autologous" transplants: the person's bone marrow is removed, frozen, and stored until therapy is complete; then the cells are thawed and reinfused.