It was a notable year for gene therapy. The first such treatments in the U.S. came to market this year after winning approval from the Food and Drug Administration. Meanwhile, researchers announced more miraculous cures of patients with rare and life-threatening diseases who were treated with experimental therapies.

Decades in the making, gene therapy—the idea of modifying a person’s DNA to treat disease—represents a major shift in medicine. Instead of just treating symptoms like the vast majority of drugs on the market, gene therapy aims to correct the underlying genetic cause of a disease. Doctors and scientists hope these treatments will be a one-shot cure.

Last year, we wrote that 2016 was gene therapy’s most promising year. But 2017 proved to be even bigger.

Sickle-cell cure

In March, researchers announced that a teenage boy in France had been cured of sickle-cell disease after receiving an experimental gene therapy developed by Bluebird Bio. Caused by a single genetic mutation, sickle-cell is an inherited blood disorder that affects 100,000 people in the U.S. and millions around the world. Scientists removed stem cells from the boy’s bone marrow and modified them in the lab by introducing copies of a gene to prevent his red blood cells from becoming “sickled.” When the treated cells were infused back into his body, they began to make normal blood cells. More than two years after treatment, the patient has enough normal red blood cells to evade any side effects of the disorder.

Cancer killers

This year the FDA approved two pioneering treatments, Kymriah and Yescarta, that use a patient’s own immune cells to fight rare types of cancer. Called CAR-T therapies, these “living drugs” are made by extracting T cells from patients and genetically engineering them to go after and destroy cancer cells. The cells are then infused back into the body. So far, these therapies are being tested only in a handful of lethal cancers as a last resort when more traditional treatments, like chemotherapy, don’t work. Kymriah treats a bone marrow cancer that affects children and young adults, and Yescarta treats a type of lymphoma. Some patients have had remarkable recoveries and remain in remission months or years later.

Building new skin

When a bacterial infection threatened his life, a boy with a devastating connective tissue disorder called epidermolysis bullosa got new skin created with gene therapy. To make it, scientists extracted cells from a part of the child’s body that wasn’t blistered. They isolated skin stem cells and added copies of a healthy version of the gene. They let these cells grow into small sheets and, in a series of three surgeries, transplanted them onto the patient’s body at a hospital in Germany. Researchers announced the groundbreaking skin graft in November.

Restoring sight

In December, the FDA approved the first gene therapy for an inherited disease. The treatment, called Luxturna, aims to correct a mutation responsible for a range of retinal diseases that make people gradually go blind. In human tests, the treatment has restored vision for more than two dozen patients who were losing their sight. It isn’t an outright cure because it doesn’t give patients normal vision, and it’s unknown yet how long the benefits last. The company that makes the therapy, Spark Therapeutics, said it won’t be announcing its price until January. Some analysts have predicted it could cost $1 million or more.

Hope for hemophilia

BioMarin is one company working on a gene therapy that replaces the faulty gene involved in the most common type of hemophilia, effectively curing the disorder. In December, the company published early clinical trial results showing that nine patients who received its therapy saw substantial increases in the blood-clotting proteins absent in hemophilia. A year and a half after treatment, patients have had fewer bleeding issues and have been able to cut back on infusions of clotting factor. Meanwhile, a handful of patients with hemophilia B, a rarer form of the disease, are already experiencing amazing cures after one-time treatments.