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Beta thalassemia is a rare genetic blood disorder that reduces the production of hemoglobin. Hemoglobin is an iron-containing protein found in red blood cells that carries oxygen to cells throughout the body.

During fetal development, the body makes fetal hemoglobin until about six months after birth, when a gene referred to as BCL11A stops its production. Ordinarily, red blood cells then produce adult hemoglobin to carry oxygen. However, when a person has beta thalassemia, a mutation or loss of the gene encoding beta globin impairs the production of hemoglobin, leading to severe anemia and the need for transfusions.

How gene therapy for beta thalassemia works

Blood stem cells are collected from a patient and genetically edited outside the body to block the expression of the BCL11A gene, which normally shuts off the production of fetal hemoglobin shortly after birth. This edit changes the genetic code in the blood stem cells to turn back on fetal hemoglobin production. After receiving conditioning chemotherapy to make room for the new cells in the bone marrow, the genetically edited blood stem cells are infused back into the patient.

The goal is to boost the production of new red blood cells to permanently increase fetal hemoglobin production. This type of treatment is known as gene editing.

Beta thalassemia gene therapy clinical trial

A Study to Assess the Safety, Tolerability, and Efficacy of ST-400 for Treatment of Transfusion-Dependent Beta-thalassemia (TDT)
Recruiting adults ages 18 to 40 years (full eligibility criteria)
Boston Children's Hospital
Started: March 2018
Principal investigators: David A. Williams, MD, and Erica Esrick, MD 
Colleen Dansereau, MSN, RN, CPN617-919-7008 or


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