Gene Therapy May Finally Be Coming of Age

Sickle cell anemia is a genetic blood disorder characterized by episodes of severe pain, anemia and other complications. In more affluent countries, life expectancy for those who suffer from the disorder is 40-60 years.

Now, in a new study out this month in The New England Journal of Medicine, scientists report that a teenage boy with the disorder remained symptom-free for 15 months after undergoing gene therapy.

"We may be on the threshold of finally being able to cure people of genetic diseases safely using gene therapy," said Stanford University's Mark Kay, a researcher in the field, in response to the study. Kay cited recent successful gene therapy treatments for hemophilia, hereditary blindness and even leukemia.

Gene therapy is a simple concept — basically scientists add a working gene to a cell with only broken ones. The working gene then makes up for the broken copies of that gene and cures the genetic disease.

But getting the right gene safely to the right spot, in enough cells for a long enough time, turns out to be a tall order. Such a tall order that gene therapy is only now coming into its own as a somewhat reliable way to treat genetic disease.

This turnaround is not due to some leap of understanding, but because of slow, incremental improvements in every aspect of the process. Scientists are better at getting more cells to take up the therapeutic gene in a much safer way.

Safer Delivery

One of the biggest changes in gene therapy occurred in the 2000s, when scientists discovered how to better deliver to the patient functioning genes.

Most gene therapies take advantage of viruses, which are very skilled at inserting themselves into a cell’s DNA, where they would usually wreak havoc.

But with gene therapy, scientists strip out the parts of the virus that make it dangerous. It's this engineered virus they use to deliver the working genes.

In early gene therapy research, scientists used retroviruses , which are easy to work with and are very good at getting genes into a cell’s DNA.

Unfortunately, many of them tend to insert themselves into places in our DNA that switch on genes that can cause cancer; that happened in a study back in 2002. Since then, scientists have worked hard to find retroviruses that wouldn’t cause this problem.

Other Important Tweaks

But a good delivery vehicle isn’t enough to treat sickle cell anemia. Scientists also need to replace the mutated genetic material that’s causing the illness with a working gene powerful enough to keep the disease at bay. In a 2004 study, scientists engineered a gene that seems to do the job for sickle cell anemia.

In the case of the boy reported earlier this month, researchers removed his bone marrow cells, used a virus to insert a working gene into them, then returned the engineered bone marrow cells back to the patient.  Bone marrow cells are where all new blood cells are made.

Another key improvement was to treat the patient with a drug, busulfan. This allowed for more of the engineered cells to take root in the patient’s bone marrow, meaning more of his red blood cells returned to normal.

“All of these changes and more have led to a successful outcome,” says Stanford genetic researcher Dr. Michele Calos, speaking of the new study. “This successful study is the culmination of more than 30 years of work by many people.”

We may be on the threshold of finally being able to cure people of genetic diseases safely using gene therapy. Or then again, we might not.

Over the years, scientists have been heralding the coming gene therapy age again and again. Each time there was a setback that held the field back.

Gene therapy is still a very expensive and time-consuming procedure, but if it can be streamlined, it holds promise for the millions of people worldwide struggling with sickle cell anemia, cystic fibrosis and other genetic diseases.

Dr. Barry Starr is a scientist in the Department of Genetics at Stanford University. He runs the Stanford at The Tech program and the Understanding Genetics website with The Tech Museum of Innovation in San Jose, California.