A few years ago, Oscar Diep, a 33-year-old software engineer living in Weymouth, Mass., started needing blood transfusions more often to manage a blood disorder called beta thalassemia. He also noticed that it was becoming harder for the nurses to find a vein for his infusions.
On top of this, Diep and his then girlfriend, now wife, were thinking about starting a family.
“I wanted to cut out the ‘going to the hospital’ part of my life,” he says.
To do that, he started thinking about pursuing a cure for the disease. An exciting new possibility caught his eye. Gene therapy for beta thalassemia was approved by the U.S. Food and Drug Administration (FDA) in January 2024.
Soon after, Diep decided to come to Dana-Farber Cancer Institute for gene therapy.
“At our center, he’s a pioneer.” says Joseph Antin, MD, chief emeritus of Stem Cell Transplantation at Dana-Farber, who oversaw Oscar’s treatment.
Oscar Diep at Dana-Farber after treatment. Credit: Johnson Photography, Inc.
A normal life
Diep was diagnosed with beta thalassemia major when he was two. He inherited two copies of a gene mutation that disables the production of a substance called beta globin. Without beta globin, the body can’t make hemoglobin, a protein in red blood cells that helps them distribute oxygen to tissues in the body.
People with two copies of the mutation — a condition called beta thalassemia major — end up not having enough functional red blood cells to survive. To replenish his supply, Diep has needed monthly blood transfusions his whole life.
Another complication of the disease is that it can result in an overabundance of iron in the body. Hemoglobin normally uses iron to assemble itself, but when hemoglobin isn’t being made because of this disease, the iron starts to build up in organs and damage them.
To remove the excess iron, Diep has received iron chelation therapy since he was a child. Before 2005, iron chelation therapy was delivered as an infusion using a pump. It took 8 to 12 hours to infuse the medicine.
“My mom was the one who prepared that and did everything for us when we were kids,” says Diep. “That was probably a little bit tough for her to have to do that for us.”
Challenges mount
Years later, during his late 20s, Diep started to notice that he was more tired a few weeks after a transfusion. He needed them more frequently. And the transfusion process was getting more complicated.
In 2022, he met with Antin at Dana-Farber to talk about a cure. Diep had heard about gene therapy several years earlier, but he was hesitant to try something so new.
They settled on an allogeneic stem cell transplant. This process would involve replacing Diep’s bone marrow stem cells with stem cells from a healthy donor. The procedure is curative, but it involves a risk. Even with the best match for a donor — someone with the same immune markers on their cells as on Diep’s — there was a risk that Diep’s body would reject the cells, and that risk had him worried.
In 2024, while preparing for the stem cell transplant, Antin mentioned that a gene therapy, called exagamglogene autotemcel (Casgevy), had been approved by the FDA. Diep was eligible to receive it because he was dependent on blood transfusions, but otherwise was healthy. In addition, the gene therapy would use Diep’s own cells, so it would have a lower risk of rejection.
Diep switched gears and opted for gene therapy.
Oscar Diep and Joseph Antin, MD, chief emeritus of Stem Cell Transplantation at Dana-Farber, who oversaw Oscar’s treatment, discuss the results of gene therapy treatment. Credit: Johnson Photography, Inc.
Newly approved gene therapy
In November of 2024, Diep’s stem cells were collected and sent to a laboratory to be edited using CRISPR/Cas9 gene editing tools.
The CRISPR edits turn on an ability for blood cells to produce fetal hemoglobin, a form of the protein produced before birth. The fetal hemoglobin replaces the faulty adult hemoglobin and removes the need for blood transfusions and iron chelation.
The idea for this therapy stems from research at Dana-Farber and Boston Children’s Hospital that led to the discovery of a gene that switches between fetal and adult hemoglobin at birth. That gene, BCL11A, turns on at birth, but gene editing tools like CRISPR can dial it back down.
“The process reverses a change that happened in his body over 30 years ago, shortly after birth,” says Antin. “You are perfectly healthy with fetal hemoglobin instead of adult hemoglobin.”
Oscar Diep and his wife Shirley Chan. Credit: Johnson Photography, Inc.
The cells were ready in May 2025. Before infusion, Diep received chemotherapy to destroy his remaining bone marrow stem cells. This process leaves room for the edited cells to fill the space, settle in, and begin making blood cells.
After infusion of the edited cells, Diep was in the hospital for about three weeks until he had recovered enough to go home. For the following six months, he’ll have weekly checkups with Antin, who will track Diep’s blood counts to make sure the edited stem cells are producing healthy levels of white blood cells, red blood cells and platelets.
“The true measure of success is that he becomes transfusion independent,” says Antin.
Looking ahead
Diep is still recovering from the therapy, but by all measures the newly edited cells appear to be working properly. Going forward, Diep will no longer need transfusions or iron chelation therapy. He also will not have to stay close to home and a hospital for frequent medical needs anymore.
“It will be nice to be able to travel and take a longer vacation if we want to,” he says.
Diep is also looking forward to starting a family, though he’s not quite ready for more big changes yet.
“I’m taking it day by day and hoping for the best,” he says.
Joseph H. Antin, MD
About the Medical Reviewer
Dr. Antin received his MD from Cornell University in 1978, and postgraduate training in hematology and medical oncology at Dana-Farber and Brigham and Women's Hospital. He subsequently served as director of the Bone Marrow Transplantation Service at Brigham from 1987 to 1997. He is Chief Emeritus of the Stem Cell Transplant Program of the Department of Medical Oncology at Dana-Farber and Brigham. He is a founding member and past president of the American Society of Blood and Marrow Transplantation and a past Chairman of the Steering Committee of the BMT Clinical Trial Network.
Written By: Beth Dougherty
Medically Reviewed By: Joseph H. Antin, MD