Vertex Pharmaceuticals and CRISPR Therapeutics announced Friday updated findings from two Phase I/II studies of CTX001 in transfusion-dependent beta thalassemia (TDT) and severe sickle cell disease (SCD), with patients continuing to show a "consistent and sustained response" to treatment with the experimental CRISPR/Cas9-based gene-editing therapy. The data were presented at the European Hematology Association (EHA) annual meeting.
The companies reported  in December last year results from 10 patients in the CLIMB-111 and CLIMB-121 studies, with follow-ups ranging from three to up to 18 months. At the EHA conference, data from 22 patients were presented, with follow-ups ranging from four months to 26 months.
Specifically, Vertex and CRISPR noted that all 15 patients with TDT were transfusion-free at last follow-up, and all seven patients with severe SCD were free of vaso-occlusive crises (VOC) from CTX001 infusion through last follow-up. Results showed that all patients with TDT had clinically meaningful improvements in total haemoglobin from 8.9 g/dL to 16.9 g/dL and foetal haemoglobin from 67.3% to 99.6% at last visit. Meanwhile, all patients with SCD had clinically meaningful improvements in total haemoglobin from 11 g/dL to 15.9 g/dL and foetal haemoglobin levels from 39.6% to 49.6% at last visit.
Reshma Kewalramani, CEO of Vertex, called the data for the potential one-time therapy "impressive in both the consistency and durability of effect." The companies noted that five patients with TDT and two subjects with SCD now have follow-up of greater than one year. "We are working with urgency to complete enrolment and look forward to finalising regulatory discussions and moving towards filing," Kewalramani added.
According to Vertex and CRISPR, the results do not include one patient with TDT who has less than three months of follow-up and who suffered a serious adverse event (SAE) of cerebellar haemorrhage. The SAE was considered related to the busulfan conditioning regimen and has resolved. The companies added that as previously reported, another patient with TDT suffered four SAEs, all in the context of haemophagocytic lymphohistiocytosis, considered related or possibly related to CTX001, which have resolved.
In April, Vertex agreed  to pay CRISPR $900 million upfront as part of an amendment to an existing partnership giving the former majority control over development and marketing of CTX001.