SAN FRANCISCO CHRONICLE (SF) - SATURDAY October 1, 1988 Edition: FINAL Section: NEWS Page: A15 Word Count: 681
David Perlman, Chronicle Science Editor

The scientists, led by Dr. Robert Gallo, reported recently at an international conference on AIDS in Tanzania that they have identified a protein that acts to stimulate the growth of the purplish clusters of cells and broken blood vessels marking Kaposi's.

The disease was named after Dr. Moritz Kaposi, the 19th century physician who first identified the lesion. It was widely known in Africa long before the outbreak of the AIDS epidemic, and is referred to by its initials, KS.

In African patients, KS is an extremely slow-growing form of malignancy and is rarely fatal, but in AIDS patients the condition can be lethal. According to the nationalCenters for Disease Control, 6,857 patients in the United States have developed Kaposi's sarcoma since the AIDS epidemic began in 1981, and 3,378 of them have died.

From Benign to Malignant

Ten years ago, Dr. Alan Rabson, a pathologist at the cancer institute, proposed a theory that in the early stages of KS the lesions are not cancerous, but that they later develop into malignant tumors.

More recently the concept has been detailed by Gallo and his colleagues to suggest that the transformation of KS lesions from benign to malignant occurs under the stimulus of proteins released by one of two major classes of cells among the many that comprise the human immune system.

The Physiology of AIDS

In the now-standard explanation of the cause of AIDS, the human immunodeficiency virus, known as HIV, infects the immune system's T cells, and the virus takes over the genetic material of the T cells to reproduce.

The cells originate in the bone marrow and grow to maturity after migrating to the thymus gland. Other bone marrow cells differentiate elsewhere in the body to become B cells, which are also involved in the immune system and produce antibodies.

In his report to the AIDS conference in Africa, Gallo noted that the class of organisms called retroviruses - including the two known AIDS viruses and others that cause certain leukemias - release little-understood proteins when the retroviruses infect human cells. The proteins are known as growth factors, and Gallo said one of those growth factors has now been isolated in his laboratory.

Mysterious Proteins

Although the protein has not been purified, it is apparently important in the development of KS lesions, Gallo said. It may also be indirectly responsible for the transformation of KS lesions from benign to malignant in people infected by the AIDS virus, he said. And it is significant, he said, that Kaposi's sarcoma can develop in people infected with the human T-cell leukemia viruses as well as those infected by HIV.

The newly discovered growth factor, Gallo said, is capable of stimulating the growth of KS tumor cells in laboratory experiments. Its biochemical nature has been partially characterized by Rabson, but the gene that governs its formation has not been cloned, nor does anyone know just how stable the protein is.

But in the experiments using the growth factor to stimulate the growth of KS cells, Gallo said, his colleagues have found that the proteins release a host of other cell products and other growth factors - all of them yet to be studied in detail.

The proteins have been injected into laboratory mice, Gallo said, and the animals develop a form of Kaposi's sarcoma that is different from the human disease and unique to the strain of mice used in the experiments.

Ultimately, he said, a deeper knowledge of the role of these growth factors in KS may lead to the development of drugs that would combat the early lesions and prevent their development into true cancers by interfering with the action of the growth factors themselves.

Two reports on the continuing KS growth factor work will be published in the journal Science later this month, the editors of that journal said. A third report is now in preparation.

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