Although a human vaccine for AIDS is most likely years away, significant progress has been made toward developing a variety of drug treatments to help its victims, scientists reported at the Third International Conference on AIDS.

More than a dozen new drugs are showing promise against the virus in laboratory experiments reported during meetings here last week. Better therapies are being used to treat the complications of acquired immune deficiency syndrome, such as the pneumonias or cytomegalovirus (CMV) infections. New strategies are beginning to emerge on how to rebuild an AIDS-damaged immune system.

Advances in the scientific understanding of the virus and the progression of the disease are enabling physicians to monitor the progress of their patients better and predict the next phases of the disease.

"It is not so much that there are new things, but we are thinking of things in new ways," said Dr. Clifford Lane of the National Institute of Allergy and Infectious Diseases (NIAID).

One example of a new approach for monitoring the progression of the disease in infected individuals who have no symptoms is just emerging from the lab. It is based on the production of certain virus proteins, such as one named p24, in an infected person that have been linked to the development of AIDS symptoms. Early in the infection, very little p24 can be found in the patient's blood, but as the disease progresses, p24 levels rise. By monitoring the levels of the p24 protein, Lane said, physicians could choose that point to begin aggressive treatment with AZT or some other drug.

Current drug therapies aimed at AIDS generally focus on two different strategies: suppressing the AIDS virus in the body and rebuilding the ravaged immune system.

AZT, the only drug approved by the Food and Drug Administration for use in AIDS patients, is only the first of a number of drugs shown to block the virus in the body. In the pipeline are dozens of chemically related drugs, such as dideoxycytidine, that may be more effective or have fewer side effects than AZT. Some of these drugs are about to be tested in humans.

A number of other drugs -- such as interferon and tumor necrosis factor -- attack the virus by stimulating the immune system to attack the invader. "The next most promising drug after AZT probably is alpha-interferon," said Dr. Anthony Fauci, NIAID director.

An early study, however, indicated that interferon failed to help patients with AIDS. Why that happened may turn out to be a valuable lesson for physicians.

All the patients in the interferon study had had their disease for a long time, Lane said. Because AIDS attacks and destroys the immune system, the longer the patient has the disease, the greater the damage to the immune system. And if it is destroyed, the immune system cannot respond to interferon stimulation and attack the virus. If the disease is treated earlier with interferon, Lane said, the drug should be more effective. Tests of that hypothesis are under way.

Beginning treatment early, before the virus has had the time to damage the body and when the body is better able to withstand the side effects of the drugs, seems to be receiving more emphasis, researchers reported.

A large study is being organized to use AZT to treat people infected with the AIDS virus but who do not have symptoms. The researchers want to determine whether AZT treatment can halt the progression of the virus and prevent symptoms from developing.

In another report, Fauci's group at the National Institutes of Health has been transplanting bone marrow from a healthy twin into the infected brother who has full-blown AIDS to see if this strategy can rebuild the immune system.

Ten AIDS patients have been treated for 12 weeks with AZT and then given bone marrow transplants from their identical twins. Some continue to receive AZT, while others do not.

One patient treated with a bone marrow transplant more than a year and a half ago, and not part of the 10-patient study now under way, is still alive after several transplants, but his course has been rocky, Fauci said. No results are yet available on the 10 patients, and it is not yet clear whether bone marrow transplants -- with or without AZT -- will become a standard treatment.

A number of other drugs are also being tested to determine whether they can boost -- but probably not rebuild -- the immune system.

One, called GMCSF, a hormone that stimulates the production of certain white blood cells, does not appear to have an immediate impact on AIDS, but it may prove useful in preventing some of the opportunistic infections associated with the disease.

Another is IL-2, a natural hormone that stimulates production of white blood cells, including those killed by the AIDS virus. Lane said that IL-2 increases the number of white blood cells in the AIDS patient, but "IL-2 {alone} is of minimal, if any, clinical benefit," he said. But if combined with other drugs such as AZT or interferon, IL-2 could become a powerful treatment.

In the late stages of the disease, AIDS patients "are like time bombs," Fauci said. They develop many different kinds of infections and some unusual cancers. Each of these must be treated as a separate disease in a patient already suffering from AIDS.

Besides progress in fighting the virus, researchers have found a number of treatments to control complications of AIDS.

Two infections, a type of bacterial pneumonia and CMV, cause many of the AIDS deaths. Trimetrexate, a drug similar to the anti-cancer agent methotrexate, appears to work against the pneumonia and cause fewer side effects. Another drug, DHGP, seems effective in controlling CMV, but it has to be taken for the rest of the patient's life.

The progress of the last few years has been rapid, a number of researchers said. Much progress has come from the ability of molecular biologists to dissect the genetic structure of the AIDS virus. Scientists have now isolated most of AIDS viral genes. Understanding the virus' basic machinery has given researchers targets for new drugs.

And the number of targets is small, Lane said. The AIDS virus has only eight genes compared to the 200 or more in CMV. Being less complex, it should be easier to stop.

Said Lane: "We are lucky it is a simple virus."