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GENE THERAPYÝADVANCE
By Sean Henahan, Access Excellence BALTIMORE (4/25/97) Early results of a pioneering gene therapy trial indicate successful activation of patients' immune systems, an important step in development of gene therapies. The results from the first human trial of a genetically engineered cancer vaccine are the culmination of more than eight years of laboratory, animal and preclinical human studies. Eighteen patients with metastatic or widespread kidney cancer received the experimental therapy at the Johns Hopkins Oncology Center. One patient, whose tumor continued to grow and spread to his lungs after surgery, obtained a substantial remission for seven months after receiving the vaccine. The rest all had measurable immune responses, but not remissions. Many patients died from their disease within the first year of the trial. "The purpose of this study was to determine whether the vaccine could cause an immune response in patients and be administered safely, and we proved that it could," says Fray Marshall, M.D., professor of urology and oncology and senior author of the study. "The patients we treated had extremely advanced disease so we did not expect to cure anybody." He cautions patients and their families that there is much more research to do before the treatment is widely available. "There have been too many promises made in the study of gene therapy, without much delivery. We proceeded slowly and cautiously, verifying and re-verifying the findings over this eight-year period. We believe these results demonstrate that the vaccine has clinical potential." The next step, he adds, is to test the vaccine in high risk patients with less widespread disease, following them over a longer period of time. Those studies will begin this year in Japan, he says. In the randomized, double-blinded study, one group of patients received a tumor vaccine with a potent immune system activating gene (GM-CSF) inserted into the cells. The other group received a tumor vaccine without the inserted gene. The vaccine therapy began with surgical removal of the kidney tumor. The researchers collected a small sample of cancer cells from the tumor and radiated them to stop growth. In the gene vaccine group, the researchers used an inactive virus, called a retrovirus, to carry the GM-CSF gene into the cancer cells. These genetically engineered cells were then injected under the skin of the patient.
Once inside the body, the GM-CSF
gene supercharges the immune system, causing it to seek and destroy cancer
cells throughout the body. Although patients receiving both types of tumor
vaccines showed immune responses, patients with the gene vaccine also showed
activation of immune cells called eosinophils, believed to be important
in antitumor immunity.
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