Vertex Pharmaceuticals and CRISPR Therapeutics have reported positive interim results from two Phase I/II clinical trials of investigational, ex-vivo, CRISPR/Cas9 gene-edited therapy, CTX001.

CTX001 involves the engineering of a patient’s hematopoietic stem cells to generate high foetal haemoglobin levels in red blood cells.

The Phase I/II trials, CLIMB-Thal-111 and CLIMB-SCD-121, are being conducted to evaluate the safety and efficacy of a single CTX001 dose in patients with transfusion-dependent beta thalassemia (TDT) and sickle cell disease (SCD), respectively.

After administration of CTX001, participants will be tracked for when the edited cells start mature blood cells production (engraftment). Subjects will then be monitored for CTX001’s effect on various disease measures.

Interim data was obtained from the first two trial participants.

In the CLIMB-Thal-111 study, one patient had neutrophil engraftment and platelet engraftment at 33 days and 37 days post-CTX001 infusion, respectively.

The patient experienced two serious adverse events (SAEs), which were considered unrelated to the investigational therapy.

At nine months following CTX001 administration, one patient was observed to be transfusion independent with 11.9g/dL total haemoglobin levels, 10.1g/dL foetal haemoglobin and 99.8% F-cells.

In the CLIMB-SCD-121 trial, neutrophil and platelet engraftment occurred 30 days after infusion. The patient had three SAEs that were not CTX001-related.

Furthermore, the patient was free of vaso-occlusive crises (VOCs) at four months, with 11.3g/dL total haemoglobin levels, 46.6% foetal haemoglobin and 94.7% F-cells.

Vertex Pharmaceuticals chairman, president and CEO Jeffrey Leiden said: “The data we announced today are remarkable and demonstrate that CTX001 has the potential to be a curative CRISPR/Cas9-based gene-editing therapy for people with sickle cell disease and beta thalassemia.

“While the data are exciting, we are still in the early phase of this clinical programme.”

The studies are designed to enrol up to 45 patients each. Participants will be followed for nearly two years from the infusion.