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What Are Gene and Cell Therapies?

Contributor: Florian Eichler, MD
5 minute read
DNA double helix

Lately, gene and cell therapies have been getting a lot of buzz—and for good reason. They hold great promise for treating diseases such as cancer, ALS, multiple sclerosis, heart disease, and more. 

As the largest hospital-based research system in the country, Mass General Brigham has more than 400 researchers studying gene and cell therapies, from basic research in the lab to clinical trials that test new therapies in patients. Gene therapy pioneer Roger Hajjar, MD, has been named director of the Mass General Brigham Gene and Cell Therapy Institute.

“This is a different class of medicine than we’ve seen in the past, and it constitutes a real paradigm shift,” says Florian Eichler, MD, a Mass General Brigham pediatric neurologist who studies the genetics of nervous system disorders.

“These transformative therapies are allowing us to treat some disorders we never thought we’d be able to treat, and they’re helping us treat others in new ways.”

Because gene and cell therapies are so new and different, many people have questions about them. What, exactly, do these new treatments do? How do they work, and what makes them so special? Consider this your Gene and Cell Therapy 101.

Different kinds of gene and cell therapies

What is the difference between cell therapy and gene therapy? They aren’t exactly the same, but they are closely related, and they sometimes overlap.

“Gene and cell therapy both belong in the realm of precision medicine,” Dr. Eichler explains. In precision medicine, doctors tailor treatments to a person based on their genes or other unique characteristics. 

Here’s how these treatments work.

Gene therapy

Many diseases are caused by mutations (mistakes) in a person’s genes. There might be a typo in the DNA. Or a gene might be missing or repeated. Gene therapy is designed to silence a mistake in the gene or replace the faulty gene with a corrected version.

Usually, doctors use viruses to deliver the healthy, corrected version of the gene into the patient’s body. The idea of infecting someone with a virus on purpose might sound strange. But the virus is altered first so it doesn’t cause any disease symptoms, Dr. Eicher explains. “We’re just using it as a delivery vehicle to drop off the gene cargo.”

Once inside, the healthy gene inserts itself into a patient’s DNA, replacing the faulty version. With the mistake corrected, the gene should begin working properly, eliminating the disease.

Cell therapy

In cell therapy, doctors transplant human cells into a patient to replace or repair damaged cells. Not all types of cell therapy are new. Blood transfusions are one common example. Transplants of stem cells from bone marrow have been used for decades to treat leukemia and other diseases.

But scientists are making new breakthroughs in cell therapy. In regenerative medicine, doctors might inject fat or bone marrow cells to help heal joint damage. And many promising treatments blend cell therapy with gene therapy. You can think of them as cell-based gene therapies.

Cell-based gene therapy

With these treatments, doctors remove cells from a patient. In the lab, experts alter those cells using gene therapy. Doctors then implant the modified cells back into the patient’s body, where they fight disease or give rise to new, healthy cells.

People often ask: Is stem cell therapy the same as gene therapy? Not necessarily. Stem cells are special because they have the ability to turn into many different cell types. Some types of cell therapy use stem cells, but others don’t.

Take CAR-T cell therapy, for example. In CAR-T cell cancer treatment, doctors draw a patient’s blood and remove the T-cells, a type of immune cell. Scientists modify T-cells in the lab and then doctors return them to the patient’s body. There, the altered cells seek out and attack cancer cells. CAR-T cell therapy has been approved to treat lymphoma and multiple myeloma, and scientists are studying its potential for treating other cancers.

All of a sudden, we’re able to address rare diseases that we’ve never been able to treat before.

Florian Eichler, MD
Pediatric Neurologist
Mass General Brigham

How many gene and cell therapies are FDA-approved?

To date, the U.S. Food and Drug Administration (FDA) has approved more than 20 gene and cell therapies, Dr. Eichler says. But researchers are studying thousands more, so that number is likely to grow quickly. “We’re going to see a huge surge in these treatments,” he predicts.

Many of those approved therapies are offering hope for people with diseases that, until now, have been difficult or impossible to treat. “All of a sudden, we’re able to address rare diseases that we’ve never been able to treat before,” Dr. Eichler says. More than 7,000 rare diseases are thought to be caused by a mistake in a single gene, he adds. Gene and cell therapy offer an opportunity to fix those genetic errors.

Researchers at Mass General Brigham are leading that effort. “In the past 2 years, the number of gene therapy trials at our hospital has more than doubled, and we expect a lot more growth to come,” Dr. Eichler says. “There are tremendous opportunities to develop new treatments.”

Headshot of Florian Eichler, MD


Pediatric Neurologist