Vertex Pharmaceuticals has reported long-term data for its gene therapy Casgevy (exa-cel) in patients with sickle cell disease or transfusion-dependent beta-thalassemia (TDT).

Currently boasting the only approved CRISPR-based gene editing therapy, Vertex presented the results from the long-term follow-up trials at the annual European Haematology Association (EHA) Congress, held in Madrid, Spain from 13 to 16 June.

The data is from more than 100 patients – 46 with sickle cell disease and 56 with TDT – treated with Casgevy.

Casgevy was approved by the US Food and Drug Administration (FDA) in December 2023 alongside bluebird bio’s Lyfgenia (lovo-cel). This was followed by a European approval in February 2024.

While gene therapies have the potential to transform the treatment of rare diseases, questions remain over long-term effectiveness and safety.

The longer-term data from Vertex’s CLIMB trials could go some way to quell any circling over Casgevy. In sickle cell disease, 92.3% of patients with at least 16 months of follow-up were free from vaso-occlusive crises (VOCs) for at least 12 consecutive months, consolidating previously reported primary endpoint data. The longest VOC-free duration was 54.8 months, whilst the mean was 27.9 months. All but one of the patients in the evaluable cohort were free from hospitalisations related to VOCs for at least 12 consecutive months.

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For TDT, 94.2% of patients with at least 16 months of follow-up were transfusion-independent for at least 12 consecutive months. The longest duration of transfusion independence was 59.4 months, whilst the mean was 31 months.

Casgevy works by reducing BCL11A expression, which allows higher production of foetal haemoglobin and stops red blood cells from turning sickle-shaped. 

In both sets of patients, edited levels of BCL11A alleles were stable over time, indicating successful editing in the long-term hematopoietic stem cells.

Vertex said in a statement: “The efficacy results are consistent with the previously reported primary and key secondary endpoints analyses from these exa-cel studies and continue to demonstrate transformative clinical benefit with durable and stable levels of fetal haemoglobin (HbF) and allelic editing.”

The US pharma company is due to present the data from its CLIMB trials at the EHA Congress. CLIMB-111 and CLIMB-121, are designed to assess the safety and efficacy of a single dose of Casgevy in patients aged 12 to 35 years with sickle cell anaemia or TDT characterised by recurrent VOCs, respectively. CLIMB-131 is designed to evaluate the safety and efficacy of Casgevy in patients who have previously taken the gene therapy in other CLIMB studies. The trial is designed to follow patients for up to 15 years after infusion.

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