Protein May Trigger Tumors in AIDS Patients, Researchers Say
A protein made in the white blood cells of AIDS patients appears to play a key role in triggering Kaposi’s sarcoma, a mysterious skin tumor that afflicts many such patients with the fatal disease, National Cancer Institute researchers reported in Washington on Monday.
The discovery of the growth-promoting factor may lead to new treatments for the tumor that either block the production of the protein or interfere with its actions.
“The practical implication may be that this tumor could be reversible,” Dr. Robert C. Gallo, a co-discover of the AIDS virus, said in a telephone interview. Kaposi’s “is driven by growth factors.”
The new data from Gallo’s laboratory was announced at the annual meeting of the American Federation for Clinical Research.
Use of the new growth factor--which has yet to be officially named--has also allowed Kaposi’s sarcoma cells to be maintained in the laboratory for more than one year, Gallo said. This will greatly assist research into the tumor. Previously, researchers had been unable to grow the tumor cells outside of the body for long periods of time.
Kaposi’s sarcoma is a rare tumor, except among people with acquired immune deficiency syndrome. It primarily causes multiple brownish or purple tumors on the skin or inside the mouth but can also affect the lymph nodes and abdominal organs. The tumor has been diagnosed in about one-sixth of the more than 60,000 reported AIDS cases in the United States.
Kaposi’s sarcoma is disproportionately common in homosexual men with AIDS, as compared to those who contract the AIDS virus through intravenous drug use or heterosexual contact. But in recent years, the frequency with which the tumor is diagnosed in all groups of AIDS patients appears to be declining.
Gallo’s new findings show that the growth factor is produced when so-called “T-4" lymphocytes are infected with the AIDS virus, as well as when they are infected with other retroviruses. The growth factor is not released under normal conditions or when the cells are exposed to other germs.
In recent years, scientists have discovered many such proteins that spur the multiplication of human cells. When secreted into the circulation by one type of cell, these growth-factor molecules influence the reproduction of other types of cells elsewhere in the body. For example, one such substance, interleukin-2, is being tested for its ability to stimulate the growth of cells that fight tumors.
Because the Kaposi’s growth-promoting agent has been only partially purified, the researchers are not sure whether they have discovered a new substance or simply detected a new action of a previously discovered protein.
“We are not 100% positive that it is novel, but everything argues that it is,” Gallo said. “The final proof is when we clone the gene,” thereby determining the protein’s genetic structure.
Discovery of the growth factor will not have “immediate implications” for how Kaposi’s sarcoma patients are treated, according to Dr. Parkash Gill, an assistant professor of medicine at Los Angeles County-USC Medical Center. But Gill said AIDS researchers will now seek to learn what drugs interfere with the body’s ability to make the protein in the hope of devising new therapies.
The new findings may also stimulate research to see if varying levels of the growth factor in the body help explain why some Kaposi’s patients have mild cases or spontaneous regression of their tumors while others quickly develop lethal disease.
But Gallo acknowledged that the discovery of the growth factor still leaves many mysteries unsolved. “We have contributed nothing to the question of why homosexual men get more Kaposi’s than anybody else,” he said.