A vaccine against the virus that causes AIDS is possible in the next decade but will require much research in several areas of biology, a leading AIDS and cancer research specialist and Nobel laureate said here Nov. 14.
"We will be able to make a vaccine. There is evidence that there is immunity," David Baltimore, molecular biologist at the Massachusetts Institute of Technology, told a packed audience in Law Auditorium, Schurman Hall. "We should focus as much money as we can on a vaccine."
Baltimore, who won the Nobel Prize in physiology or medicine in 1975 for discovering in 1970, simultaneously with Howard Temin, the enzyme reverse transcriptase, made his comments at the Ef Racker Lectureship in Biology and Medicine, sponsored by the Section of Biochemistry, Molecular and Cell Biology. His talk was titled "Can There Be a Vaccine Against AIDS?"
"When I was heading the National Academy [of Sciences] study 10 years ago, we said publicly it would be possible in five years, but most of us were thinking 10. Well here it is 10 years, and I would say it will take another 10 years," Baltimore said in response to a question, and added, "you can't predict a breakthrough; otherwise, it's not a breakthrough."
Baltimore, a member of the National Academy of Sciences and former president of Rockefeller University, said that there have been about a half-million cases of AIDS in the United States as of 1995 and 316,000 deaths. "This epidemic has built up, although the actual rate of increase has slowed since the early 1990s," he said.
The nature of the epidemic has changed as well, he noted. Although the greatest portion of infected people in this country are gay men, he said, intravenous drug users "are now a more serious problem than ever before. Heterosexual cases are increasing, and there is a growing problem of infection of children," he added. Also, the median age of AIDS patients who die from the disease in this country is 35.
"To me, this is the greatest tragedy, that so many people in the prime of life are dying," Baltimore said.
But there is a more compelling reason why a vaccine is needed, he said: "It's not because of AIDS in this country but because of a worldwide epidemic. The latest number I heard is that 23 million people worldwide are infected. The rates of increase are remarkable. We need all the resources we can get in vaccine development."
The molecular biologist, who helped found and was first director of the Whitehead Institute of Biomedical Research Center at MIT, said that this year has produced some exciting advances in AIDS research. A new drug therapy, based on protease inhibitors in combination with AZT and other drugs, has given new hope to AIDS patients, two of whom, Andrew Sullivan and David Sanford, wrote about their therapies recently in the New York Times and the Wall Street Journal, respectively, where they work. Protease is an enzyme that HIV -- the virus that causes AIDS -- needs to infect immune system cells.
But long-term drug therapy will be difficult, Baltimore said, because "the virus changes rapidly; it's toxic to cells, and it requires leading-edge drug design."
Although it's good to see renewed optimism such as that displayed by Sullivan and Sanford, Baltimore said, it is too early to tell if this new regimen will work.
"Because these drugs are so new, we don't know for how long they can work and what possible side effects are and whether resistance will develop. We've got a long a way to go." But he said that the articles represent "a change in thinking about the epidemic."
Baltimore outlined why he thought a vaccine was possible, describing how antibiotics are useful only against bacteria. Vaccines are used against viruses. Live attenuated vaccines, such as those for polio and smallpox, don't work against HIV in humans, although they do for some non-human primates.
The virus does its lethal work by attaching to key cells in the body's immunity arsenal, lymphocytes known as CD4 cells. These cells are critical to the body's mounting an attack against the alien invader virus cells, but the CD4 cells are killed within 48 hours of infection. Attenuated vaccines use live cells of the virus itself; the immune system kicks in and inoculated people's bodies mount a successful attack, preventing future infection. But that does not work with HIV, in part because the body never has a chance to mount an attack.
In addition to the combination drug therapies, among other major advances this year, Baltimore said, is that "we've learned that the viruses are continually multiplying," even though it takes about 10 years from the time of infection for the disease to occur. Also, "the amount of virus in a patient's blood is a good predictor of disease progression, and it takes two receptors for the virus to get into the cell. We've learned that just in the last six months."
But Baltimore said he believes a vaccine for humans is possible because there is evidence from infected people that immunity does exist. In 5 percent of the infected population, CD4 cells never decrease.
"Sex workers [male and female prostitutes] primarily in Africa have repeated, multiple exposures yet remain uninfected," he said. "Infected people rarely show signs of super-infection," that is, infections that worsen with repeated exposures, "and there is some protection against HIV1 in HIV2-infected people."
Also there is evidence, he said, that there is some "set point," a level at which the virus remains in the bloodstream without causing the disease.
The Ef Racker Lectureship is named for Efraim Racker, the late Albert Einstein Professor of Biochemistry and chair of the Section of Biochemistry at Cornell.