Killer-cell infusions fight viral diseases.

Infusions of white blood cells called killer T cells can arm bone marrow transplant recipients against a virus that often causes deadly lung infections among such patients, according to the results of a new study.

Researchers speculate that the treatment might also benefit AIDS patients, who are vulnerable to infection with the same virus. A similar strategy, they suggest, might also help AIDS patients combat HIV, the virus that causes AIDS.

The treatment consists of taking uninfected killer T cells from the blood of healthy people who have been exposed to a particular virus and inserting those cells into a sick person infected with the same virus. The previous exposure primes the killer cells to attack and eradicate the patient's infected cells. Otherwise, such infected cells could serve as founts of continuing infection.

In the new study, a group of researchers at the Fred Hutchinson Cancer Research Center in Seattle infused killer T cells isolated from bone marrow donors exposed to cytomegalovirus (CMV) into three cancer patients who had received bone marrow transplants as part of their treatment. The group, led by immunologist Stanley R. Riddell, hoped that the killer cells would prevent the transplant recipients from succumbing to a CMV infection while their own immune systems were recovering.

CMV only causes illness in people with impaired immune systems. Bone marrow transplant recipients -- as well as patients who receive whole-organ transplants -- are at risk because they must take immunity-suppressing drugs to avoid rejecting their new grafts. Even a month after transplantation, two-thirds of all bone marrow recipients lack sufficient T cells to ward off CMV infection, according to previous studies. And despite treatment with the antiviral drug ganciclovir, half of all bone marrow transplant recipients who develop a CMV infection die, usually of CMV pneumonia.

CMV's effects in AIDS patients are similarly grim. While few AIDS patients develop CMV pneumonia, most carry a CMV infection, which can contribute to weight loss and wasting. Roughly 20 percent of all AIDS patients also develop CMV retinitis, an infection of the retina that can progress to blindness (SN: 10/26/91, p.260).

To test their new anti-CMV preventive, Riddell's group administered four weekly doses of roughly 2 billion CMV-exposed killer T cells to each of the three bone marrow recipients. The researchers selected only those cells that were incapable of attacking the recipients' own cells and causing graft-vs.-host disease.

Riddell and his colleagues report in the July 10 SCIENCE that the cell infusions boosted the bone marrow transplant recipients' ability to kill CMV-infected cells. In test-tube experiments, they found that blood from the recipients could kill just as many, if not more, CMV-infected cells as blood from the marrow donors. Moreover, none of the recipients fell ill from a CMV infection or developed side effects from the treatment.

Riddell says his group plans to confirm the efficacy of the treatment in a larger number of bone marrow transplant recipients. In addition, they are preparing to treat their first AIDS patient with HIV-exposed killer T cells "within a couple of months." Riddell and his colleagues also plan to infuse AIDS patients with CMV-exposed killer T cells to help them ward off CMV infection.

The success of Riddell's group in preventing CMV infection among bone marrow transplant recipients "is certainly going to have a positive impact on the efforts to use HIV-specific [killer T cells] in HIV-infected individuals," says Anthony S. Fauci, director of the National Institute of Allergy and Infectious Diseases in Bethesda, Md. "This is an interesting and important step in the right direction."