Dr. Rachel Huckfeldt, seen above in an exam room at Massachusetts Eye and Ear in Boston, Dec. 19, 2018, is leading gene therapy clinical trials. (Greg Saulmon / The Republican)

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Shawn Devenish was a toddler when doctors realized he had trouble seeing. By age 8, he had been diagnosed with retinitis pigmentosa, a rare genetic disorder that involves a loss of cells in the retina.

Devenish had no color vision, no night vision and saw everything as if through a tunnel. He couldn’t play outside after dusk. As a teenager, he couldn’t drive. He struggled to read.

Devenish adapted. He played varsity football, wrestled and did track. He was licensed as a physical education teacher. Now 26 and living in Salisbury, he works as a teacher’s aide at a school in Byfield and is engaged to be married.

But until recently, Devenish could not go outside alone after dark. He struggled coaching night football games and teaching wrestling in dimly lit gyms.

That changed in September 2018, when Devenish’s doctor offered him gene therapy.

The cutting-edge treatment has the potential to revolutionize the way diseases are treated.

Michael Sherman, senior vice president and chief medical officer at Harvard Pilgrim Health Care, a Wellesley-based insurer, called the potential of gene therapy “truly transformative.”

“The model has always been treating disease on a chronic basis,” Sherman said. “The opportunity to go in and fix a defect at a genetic level ... offers the opportunity to not just manage diseases, but cure them.”

It is no exaggeration to say gene therapy changes -- and saves -- lives.

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Essentially, gene therapy involves introducing a new gene into someone’s body to cure a disease. For example, a healthy gene might be introduced to replace a mutated gene.

Take Luxturna, the treatment Devenish received at Massachusetts Eye and Ear. Luxturna targets patients with inherited retinal disease due to mutations in a particular gene that makes a protein needed for vision.

Luxturna is a one-time treatment in which a working gene is surgically injected into the eye during an outpatient procedure while the patient is under anesthesia. The working gene causes the cells in the retina to produce the protein, which results in improved vision.

While Luxturna does not fully restore vision, it allows patients to navigate the world in dimmer light.

After the procedure, Devenish’s night vision improved. He can now walk alone at night as long as he is in a familiar place.

"It’s the freedom to go places without relying on someone else,” Devenish said.

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The first gene therapy approved by the U.S. Food and Drug Administration for use in the United States was Kymriah, which was approved in August 2017 to treat a form of pediatric leukemia.

In October 2017, the Food and Drug Administration approved Yescarta to treat a type of adult non-Hodgkin lymphoma.

Both of these are referred to as CAR-T therapies. The way they work is a patient’s cells are collected, then genetically modified in a lab to include a new gene that kills cancer cells. The cells are given back to the patient, and the new gene attacks the cancer cells.

Both therapies can have serious side effects. They have been approved to treat patients who have not responded to other treatments, or whose cancer has recurred, and who have few options left.

In clinical trials, 83 percent of Kymriah patients and 51 percent of Yescarta patients went into remission, according to the FDA.

The only other gene therapy to receive FDA approval so far is Luxturna.

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Greg Saulmon / The Republican

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But while only three gene therapies are FDA-approved, more are on the way.

A recent report by the pharmaceutical trade association PhRMA identified 289 gene and cell therapies in clinical trials or awaiting FDA approval. More than 100 are for cancer, with others focused on eye problems, cardiovascular disease, neurologic disorders and blood disorders.

Mike Ybarra, vice president of medical affairs and strategic alliances at PhRMA, acknowledged that some will never reach the market, but he said the number of therapies in the pipeline is promising.

“This is really challenging science,” Ybarra said. “It’s something most people won’t believe is real because it is so complicated.”

Ybarra said many of the treatments are for rare diseases or serious chronic diseases. “The idea would be you can use this technology to have a potentially one-time application or use, and that significantly alters the course of that patient’s life,” Ybarra said.

The next therapy likely to be approved is a one-time gene replacement therapy for spinal muscular atrophy called AVXS-101. According to drugmaker Novartis, the therapy could be available in the U.S. market in 2019.

Thomas Barker, a health care attorney at Foley Hoag, estimated that five to 10 gene therapies could be approved in the next couple of years.

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These therapies are already making a difference in Massachusetts.

Dr. Rachel Huckfeldt is leading gene therapy clinical trials for blindness at Mass. Eye and Ear. She works with Dr. Jason Comander, the surgeon who treated Devenish with Luxturna.

Huckfeldt said inherited retinal disorders — some of which can cause total blindness — affect one in 3,000 people. Until Luxturna was approved, there was no treatment for them. Now, she said, around a dozen gene therapy trials are underway to treat these diseases.

“Gene therapy gets to the root of the problem,” Huckfeldt said. “If a gene is misspelled, making either no protein or insufficient or abnormal protein, by putting a correctly spelled gene into the retina, you can solve the problem.”

Huckfeldt said the ongoing trials provide hope for patients.

“Just that the ball is in motion here, and there are these new therapies on the horizon that are being tested, is a tremendous source of hope for patients, because they’ve been told all their lives in many cases that there’s no treatment for them,” Huckfeldt said.

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Manny Johnson shows a tattoo of the sickle cell disease awareness ribbon during an interview at Boston Children's Hospital on Dec. 19, 2018. In May 2018, Johnson became the first patient ever to try a new gene therapy to cure sickle cell disease, in a clinical trial run by Boston Children's Hospital and funded by the National Institutes of Health. (Greg Saulmon / The Republican)

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Manny Johnson, 21, of Mattapan, was diagnosed with sickle cell disease when he was 3 years old. He had two strokes as a child and has undergone monthly blood transfusions since then to prevent problems.

When babies are first born, their bodies make fetal hemoglobin. Soon after birth, the body stops making fetal hemoglobin and begins making adult hemoglobin. In people with sickle cell disease, that adult hemoglobin sickles. That means a mutation in the hemoglobin molecule distorts red blood cells into a crescent shape.

This blocks the cells from passing through blood vessels and delivering oxygen to organs and tissues. Symptoms can include anemia, severe pain, respiratory problems, eye problems, strokes and kidney damage.

Johnson’s half-brother Aiden, 7, also has sickle cell disease.

The only cure is a bone marrow transplant — a potentially risky treatment that requires a matching donor.

In May 2018, Johnson became the first patient ever to try a new gene therapy to cure sickle cell disease, in a clinical trial run by Boston Children’s Hospital and funded by the National Institutes of Health.

“I wanted to do history-making stuff,” Johnson said. “Everybody wants to make history before they leave; I guess this is my little imprint on the world.”

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In the gene therapy that Johnson underwent, a gene is introduced into the body that knocks down the gene that represses fetal hemoglobin after birth. The idea is for the body to restart making fetal hemoglobin, which cannot sickle, and reduce its production of sickling hemoglobin.

For Johnson, the experience was difficult. He spent around 35 days in the hospital. His blood cells were collected, then he underwent aggressive chemotherapy, which caused painful side-effects. Finally, he received an infusion of his genetically modified cells.

It worked, and Johnson’s body began producing fetal hemoglobin.

“We’re thrilled with the results so far,” said Dr. Erica Esrick, co-principal investigator on the clinical trial and a pediatric hematologist-oncologist at Boston Children's Hospital.

Johnson has had no blood transfusions since the treatment. He is symptom-free, and his blood is back to normal, with no sickled cells. He will be monitored for 15 years to measure the long-term effects of the treatment. So far, he has felt no negative side-effects.

The Children’s Hospital pilot study has enrolled seven patients, and the hospital hopes to expand it. Meanwhile, other hospitals are experimenting with slightly different gene therapy treatments.

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Dr. Erica Esrick speaks with a reporter at Boston Children's Hospital on Dec. 19, 2018. Esrick, a pediatric hematologist-oncologist at the hospital, is the co-principal investigator on a clinical trial for a gene therapy treatment of sickle cell disease. (Greg Saulmon / The Republican)

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“Not too long ago, there were no brand-new therapies for sickle cell,” Esrick said.

To have promising therapies that can cure the disease rather than manage the symptoms, she said, is exciting. “Our goal is to have a one-time intervention that doesn’t need to be done again,” Esrick said. “It’s something many patients are really eager for, so they don’t have to take medicine every day for the rest of their life.”

Research is ongoing in areas like ways to make the chemotherapy easier.

For Johnson, he still likes to travel, play video games and go to the gym. He works for his mother’s business, which helps clients improve their credit, enjoys making YouTube videos and hopes to become an entertainer. He is happy to talk about his treatment as a way to encourage others to never feel limited by a disease.

“I like to just relax and enjoy life, smiling and laughing, because life is about happiness to me,” Johnson said. “And to inspire the world, one person at a time.”