Chicago Tribune (CT) - SUNDAY May 10, 1987 Edition: FINAL EDITION Section: TEMPO Page: 7 Word Count: 1,637
Ronald Kotulak, Science writer

Scientists generally believe that a vaccine against the AIDS virus is the only way to stop the epidemic, but many are convinced that such a vaccine is a long way off--and may never be achieved.

This is because the AIDS virus appears to have an uncanny ability to evade the body's immune system, which evolution took millions of years to perfect. Eventually the virus can destroy the immune system.

The AIDS virus is a member of the family called retroviruses, which in 1978 were discovered to cause human disease. In addition to AIDS, two forms of human leukemia are known to be caused by retroviruses, and no vaccines have been developed against them.

The genetic material of the retrovirus is made of ribonucleic acid (RNA), a cousin of dioxyribonucleic acid (DNA), which makes up the genetic code in humans.

Once inside a cell, the AIDS virus releases an enzyme called reverse transcriptase that uses the cell's machinery to make DNA copies of the virus. These DNA copies then merge with the cell's genetic code and become a permanent part of the cell's genetic makeup. The DNA viral genes are passed on to daughter cells during cellular multiplication.

From their command post in the cell's DNA, the viral genes can direct the production of more AIDS viruses under conditions that scientists do not fully understand. They direct the cell to build new RNA AIDS viruses out of the chemicals normally found in the cell.

What triggers a cell to start making more AIDS viruses is unknown, but it seems to be linked to the stimulation of the immune system, such as when the immune system is called upon to fight an infection caused by another germ.

At the same time, the virus itself seems to be safe from the body's immune defenses for two reasons: Because it becomes part of the cell's genetic code, it is not recognized as foreign by the immune system, and the viruses that are ordered to be produced from the viral genes encoded in the cell's genetic code can be transmitted directly from one cell to another cell.

By going from one cell directly to another, the AIDS virus does not have to circulate freely in the blood where it would encounter the immune defenses that normally attack viruses. Thus the AIDS antibodies that are produced cannot wipe out the hidden viruses, but they do serve as a blood test to show that a person has been infected by the virus.

"We have to accept the possibility that a truly effective vaccine may not be a likelihood," said Dr. Gary Noble, AIDS coordinator for the National Institutes of Health.

Most infectious diseases, such as smallpox and measles, have been subdued by vaccines. Vaccines, which usually contain a killed or weakened form of a disease-causing germ, stimulate the body's immune defense system into manufacturing antibodies against the real germs.

Antibodies are chemical soldiers that prowl the bloodstream. When a virus or bacteria invades the body, the vaccine-produced antibodies spot the invaders and promptly gear up the immune system to destroy them. These invading germs are vulnerable to attack because they circulate freely outside cells.

Unlike other viruses, once the AIDS virus infects a person, it becomes a permanent part of the victim's genetic makeup: The infection is lifetime, and the person is believed to be infectious all the time.

The AIDS virus not only hides from the immune system, it hides in the T-4 lymphocytes, white blood cells that are the heart of the immune system. The virus' lethal nature stems from its ability to kill these critical cells.

It is this destruction that enables otherwise harmless germs to take hold in a victim's body and cause a variety of opportunistic infections that eventually result in death. The term acquired immune deficiency syndrome was coined to describe this destruction.

Furthermore, the protein coat of the virus, which allows the viral genes to penetrate cells, constantly mutates, potentially making a vaccine against one strain of the virus useless against another.

Complicating the issue even more was the announcement last week in the New England Journal of Medicine that a team of French researchers from the Pasteur Institute in Paris have discovered a second AIDS virus in West Africa. The new virus, labeled HIV 2 for human immunodeficiency virus 2, is similar to but not identical to HIV 1, and it appears to cause the same kind of disease as the first AIDS virus.

In view of these problems, the National Institutes of Health estimates that, if a vaccine can be developed, it will not be before the mid-1990s. Dr. C. Everett Koop, U.S. surgeon general, takes an even gloomier view, predicting that an AIDS vaccine will not be available this century.

The virus can remain dormant for years. In one recent study, 14 percent of victims had developed AIDS within five years of infection, 25 percent after six years and 36 percent after seven years, the longest the study group has been followed. Overall, more than 70 percent of the people who have been infected at least seven years ago have developed AIDS, leading some experts to predict that all of those infected may eventually develop the fatal disease.

To date, the great majority of those infected fall into the principal risk groups: homosexuals, bisexuals and IV drug users. The virus has been transmitted primarily through the exchange of semen and blood, but there have been cases in which vaginal secretions have served as the agent of transmission.

Despite pessimistic assessments, "there are reasons to be optimistic," said Dr. D. Peter Drotman, a member of the Centers for Disease Control's AIDS task force. "When we started with AIDS in 1981, there was hardly anybody working on it. Now, there's hardly any good people who are not working on it. Thousands of the best scientists in the world are working on this problem."

The Federal Food and Drug Administration recently received two applications to test experimental AIDS vaccines in humans, and some human tests may begin this year. In addition, another four to six vaccines are being researched by medical institutions and drug companies.

Dr. Daniel Zagury of the Pierre and Marie Curie University in Paris reported last month that he had injected himself and a small number of people in Kinshasa, Zaire, where AIDS is pandemic, with a vaccine made from part of the AIDS virus' protein coat.

Although it seems that the race to develop an AIDS vaccine has gotten off to a quick start, many experts believe it will be years before scientists know if it is even possible to develop an effective vaccine. Vaccine research also raises questions about the ethics of testing the vaccine on humans.

Because of the emergency nature of the AIDS epidemic, some short cuts and risks will have to be taken to develop a vaccine, said Dr. Allan Goldstein of George Washington University. Goldstein and his colleagues have developed a synthetic vaccine using a part of the inner protein coat of the AIDS virus that they hope will overcome the problem with the virus' changing coat.

Twelve volunteers have been selected at George Washington and another 12 at the Institute for Immunological Disorders in Houston to get the experimental vaccine if the FDA approves their application.

Yet drug companies are reluctant to bring a new vaccine on the market, especially one potentially fraught with problems like an AIDS vaccine, without federal government protection against liability suits. Sometimes, adverse side effects from vaccines do not appear until years after a vaccine is administered, as was the case with the swine flu and measles vaccines.

Remarkable progress has been made in understanding the AIDS epidemic, thanks to modern molecular biology. Three years after the deadly infection was identified in 1981, the virus was discovered.

"If this epidemic had hit us in 1960 we would have been in a real panic situation, probably 1,000 times worse than now because we didn't even know that these viruses existed then," said Dr. Robert Gallo of the National Cancer Institute, a discoverer of the AIDS virus. "We would still be blaming semen for causing the disease."

Fortunately, the AIDS virus is hard to catch, said Dr. June Osborn, dean of public health at the University of Michigan. Unlike other major infectious organisms that can be spread through the air or through water, the AIDS virus is transmitted through sexual intercourse or sharing IV needles contaminated with infected blood.

Some scientists believe that the reason the AIDS virus is hard to catch is because of its preference for passing from one cell to another.

That may also explain why there is no evidence that the AIDS virus can be transmitted through casual contact with an AIDS victim. There is no transmission because there is no direct cell to cell contact from using doorknobs, sharing bathrooms or touching other things used by an AIDS patient.

"There has never been an epidemic in which science so quickly told people how the infectious agent was transmitted and developed strategies to cope with it," she said.

"Even in the absence of a vaccine you can avoid this virus," said Osborn. "You couldn't avoid measles, polio or the flu because the germs that caused them were airborne. But you can avoid this virus by deciding you want nothing to do with multiple sex partners, unknown sex partners and intravenous drug use."

Globally, an estimated 5 to 10 million people are believed to have been infected with the AIDS virus, and cases have been reported in 99 countries.

CAPTION: Graphic: AIDS virus at work. Chicago Tribune Graphic; Source: The National Cancer Institute.

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