Gene therapy for sickle cell disease and thalassemia

Thalassemia and sickle cell disease are among the most frequent monogenic hereditary diseases. Access to transfusions, iron chelation therapies and drugs such as hydroxyurea have improved life expectancy and quality of life. However, these diseases still cause significant disability. The first available curative therapy, bone marrow transplantation, is unfortunately not feasible for all patients. Over the past decade, numerous studies have focused on finding new curative therapies, and many clinical trials have evaluated different gene therapy approaches.

The therapeutic targets focus on adding functional copies of the gene encoding β-globin in defective CD34 + cells, mainly using lentiviral vectors directed towards HSCs. More recently, the focus has shifted to inducing fetal hemoglobin production at therapeutic levels or repairing the underlying molecular defect, using novel gene editing techniques involving CRISPR-Cas9, transcription activation-like effector protein nucleases, zinc finger nucleases and base editing. Preclinical and clinical studies now focus on optimizing how gene therapy is performed and delivered to reduce or eliminate myeloablative treatment and its potential adverse events.

In this review, we explore the potential to induce fetal hemoglobin production at therapeutic levels or to repair the underlying molecular defect that causes the disease genetically. Here, we review recent gene editing studies that are opening a new era in curative treatment for hemoglobinopathies.