Researchers Inject Genes in 2 Fights Against Disease : Human genetics: The tests against a deadly cancer and cholesterol may refine technique for DNA therapy.
In the latest advance in the genetics revolution, physicians have directly inserted a gene into humans in an attempt to cure a deadly disease, University of Michigan researchers announced Tuesday.
The researchers injected the gene, encased in small globules of fat, directly into the tumor of a 67-year-old woman with metastatic melanoma, the most deadly form of skin cancer, in hopes that the added gene would stimulate the immune system to attack tumor cells. Although the researchers hope that the condition of the woman, the first of 12 patients to be treated, will be improved, the procedure is now being tested primarily for safety.
Previous attempts at gene therapy have involved modification of cells removed from the body followed by re-injection, a procedure some believe to be safer. But many researchers believe that the future of gene therapy lies in “direct injection” techniques.
If such techniques are effective, “they would provide a much simpler and less costly alternative” to modifying cells outside the body, said geneticist A. Dusty Miller of the Fred Hutchison Cancer Center in Seattle.
Only when direct-injection techniques are perfected, said molecular biologist W. French Anderson of the National Cancer Institute, will gene therapy “have a major impact on the health care of our population.”
A second group at the University of Michigan also announced Tuesday that it has begun gene therapy for an inherited form of high cholesterol that sharply increases the risk of heart disease. The effort, in which liver cells were modified outside the body and re-injected into a 29-year-old Canadian woman, marks only the second time in the United States that a disease other than cancer has been treated with gene therapy.
The two efforts are part of a variety of human gene therapy experiments that are under way or scheduled to begin this year as the once-controversial approach to treatment gains wider acceptance. “We have begun to use DNA as a drug,” said Michigan molecular geneticist Gary J. Nabel, who conceived the melanoma treatment. DNA (deoxyribonucleic acid) is the genetic blueprint of life.
The experiments offer the hope that eventually any doctor will be able to use gene therapy in the office to treat a wide variety of life-threatening diseases.
Nabel’s approach to cancer treatment is to “mimic the process of organ rejection that occurs in transplants,” he said. In transplant rejection, the body targets proteins, called transplantation antigens, on the surface of cells in the new organ, causing the immune system to attack it.
Most cancer cells do not bear such antigens on their surface, but Nabel has developed a way to put them there. Of the 13 human trials of gene therapy now in progress worldwide, Nabel’s is the only one that does not use a virus to insert the added gene into cells.
Rather, Nabel and his colleagues take the gene for a transplantation antigen called HLA-B7 and encapsulate it in fat particles called liposomes. When the liposomes are injected into the tumor, they bind to the surface membranes of the tumor cells and carry the HLA-B7 genes into the interior of the cells.
Genetic machinery within the cells produces the antigens, which travel to the cellular membrane, where they are recognized and attacked by the body’s immune system. In the process of attacking these cells, Nabel said, “the body also learns to recognize tumor cells that haven’t been modified” and attacks them as well.
Studies in animals have shown that the technique produces a sharp reduction in tumor size and numbers.
Nabel and his colleagues will treat 12 patients in their trial of the technique. Like the first woman, whose identity is being kept confidential, all have metastatic melanoma, which kills 6,700 Americans each year. Although the technique could be used for other types of cancer, melanoma was chosen because the skin tumors are readily accessible and no invasive medical procedures are necessary.
Those selected to participate in the trials have a life expectancy of less than one year and will not benefit from further standard treatment, such as surgery, chemotherapy or radiation.
Nabel cautioned that the first trials are designed only to show safety of the technique and to determine the proper dosage of the gene. “There is a possibility that the tumors will respond, but it is unlikely,” he said, because the doses will be relatively small. “If these patients are OK after the treatment, then we will become more aggressive” in attacking the tumor.
Many ethicists have been concerned about attempts to genetically modify cells within the human body because of the risks that the viruses normally used in such attempts might modify other cells as well, causing severe side effects. The use of liposomes, plus their direct injection into the tumors, sharply reduces the risk of other cells being inadvertently modified, Nabel said.
A small risk remains nonetheless, he added, and one of the goals of the trials is to look for such inadvertent modifications.
The procedure was conducted on the Michigan woman last Thursday. She tolerated the injection well, Nabel said, and was discharged from the hospital over the weekend.
The second clinical trial involves patients with a rare genetic disorder called familial hypercholesterolemia. Patients with the disease have an abnormal gene that is the blueprint for a liver-cell protein called an LDL receptor. LDL, or low-density lipoprotein, is the so-called “bad” form of cholesterol. The receptor allows the liver to remove LDL from the bloodstream before it builds up to life-threatening levels.
About one in every 500 Americans has one abnormal LDL receptor gene, which causes elevated levels of cholesterol and heart attacks. About one in every million has two defective genes, having received one from each parent, which allows cholesterol to build up at a very early age. One-third of children who inherit two bad genes have heart attacks by age 10. This group, with two defective genes, is being treated by University of Michigan molecular geneticist James Wilson and his colleagues. The two other patients to be treated have not been chosen, but probably will be adults.
Last Friday, surgeon Steven Raper removed about 15% of the Canadian woman’s liver, simultaneously inserting a catheter into an artery leading into the liver. The liver cells were taken into a laboratory and treated with a specially modified virus that inserted a healthy gene for the LDL receptor into their DNA.
On Monday, about 1 billion modified cells were infused into the woman’s liver through the catheter. Research in rabbits indicates that the cells will lodge in the liver and begin producing the receptor. That research suggests that having a healthy receptor on as few as 5% of the liver cells leads to a significant reduction in blood cholesterol levels.
Wilson has permission to attempt the procedure in two other patients, who are now being selected.
Gene Therapy of Malignant Melanoma
Using a new approach to human gene therapy, Michigan researchers hope to get the body to reject tumors in the same manner that it rejects transplanted organs.
1. The gene for a transplantation antigen (a protein that marks the cells as being foreign) is encased in fat globules and injected directly into the tumor.
2. Inside the tumor cells, the gene produces the marker protein, which accumulates on the surface of the tumor cells.
3. The marker protein makes the immune system think that the tumor is a foreign object. Antibodies recognize the marker protein and attack the cancer cell
4. Cell dies.
