U.S. government researchers are expanding use of gene therapy to fight cancer, turning the human immune system against a deadly tumor found in young adults.
The approach may shrink tumors in many patients with common cancers, said Steven Rosenberg, chief of surgery at the National Cancer Institute’s Center for Cancer Research in Bethesda, Maryland. In a study, 9 of 17 patients with advanced cancer that had withstood other treatments saw tumors shrink after gene therapy, according to results published today in the Journal of Clinical Oncology.
The researchers genetically modified each patient’s immune system so it would recognize antigen produced by cancer cells and destroy them. The approach worked five years ago in a small study that targeted melanoma. The new work uses an antigen produced by many tumors, including some in breast, prostate, lung and ovarian cancer, though only certain patients with synovial cell sarcoma and metastatic melanoma were included in the study.
“It’s not a vial off the shelf,” Rosenberg, the lead investigator for the study, said in a telephone interview. “It’s the ultimate in personalized medicine because we are making a new drug for every patient.”
The treatment takes a patient’s white blood cells, called lymphocytes, amplifies their number and activity, and gives them back, Rosenberg said.
“We have now shown that this gene therapy, this genetic engineering of the immune system, can work not only on melanoma but on sarcoma,” he said. “We’re now looking to see if it will work on other cancers.”
Cancer is the second-leading cause of death in the nation, after heart disease, yearly killing almost 570,000 people, according to the American Cancer Society, based in Atlanta. Each year, more than 1.5 million people in the U.S. are diagnosed with cancer.
Companies, including New York-based Bristol-Myers Squibb Co. and Pfizer Inc. and Seattle-based Dendreon Corp., are devising drugs, therapeutic vaccines, antibodies and other treatments to augment the immune system’s cancer-fighting efforts. Rosenberg’s approach is a single therapy, infused in patients during 10 days in the hospital, that alters the immune system so it can see and fight cancers producing an antigen dubbed NY-ESO-1.
The immune system typically fights infections caused by bacteria, viruses and fungus after detecting antigens, substances that trigger antibodies. The gene therapy alters the immune system’s infection-fighting white blood cells so they have a receptor that sees antigens produced by many cancer cells as foreign invaders.
The study researchers obtained the gene that they used from a former cancer patient whose immune system inexplicably identified the NY-ESO-1 antigen. The gene, which helps produce a receptor that matches with the antigen, isn’t normally part of the immune system.
The human body naturally makes the antigen during fetal development. It is later produced by cancer cells, though no normal adult cells make it, Rosenberg said. As a result, only malignant cells would become vulnerable after the genetically engineered cells are put back in the body.
In the study, four of six patients with synovial cell sarcoma saw tumors shrink after getting the gene therapy. One patient had a partial response that lasted 18 months. The cancer, which affects the soft tissue that lines tendons and cavities in joints such as knees or elbows, is often fatal in patients with advanced disease.
Five of 11 patients with metastatic melanoma had tumors shrink, including two who had complete regression. In the earlier melanoma study, which used a different antigen to target the tumor, one patient remains cancer free more than five years after treatment, Rosenberg said.
“We’re giving patients the cells that can directly kill the cancer,” Rosenberg said. “All of these patients have had surgery, extensive chemotherapy, and some radiation therapy, and the cancer has grown through all of it. We are treating patients that have no other options.”
At the moment, the therapy is available only at the National Cancer Institute. The researchers have conducted trials in lymphoma patients and have approval to start tests in other tumors. The scientists have sent samples of the vector, or virus, used to modify the lymphocytes to investigators around the U.S., so additional trials may be conducted, Rosenberg said.
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