Vertex and CRISPR Therapeutics unveil more positive gene therapy data, but busulfan again casts a shadow over the field
Less than 12 hours after revealing a flop on its second shot for alpha-1 antitrypsin deficiency, Vertex plowed ahead with another data drop from its partnership with CRISPR Therapeutics. And though the topline proved positive, concerns over conditioning agents continue to linger over the collaboration, as well as the entire gene therapy space.
Presenting data from two trials at the European Hematology Association annual meeting, the pair announced that follow-up data of at least three months for 22 patients with genetic blood disorders indicated a “consistent and sustained” response to the experimental drug CTX001. All 15 patients with transfusion-dependent beta thalassemia did not need further blood transfusions and all seven with severe sickle cell disease were pain free, the biotechs announced.
There was one patient not included in the data cutoff of March 30, however, who experienced a cerebellar hemorrhage less than three months after being treated. The serious side effect was related to the busulfan conditioning gene therapy patients undergo before receiving treatment, Vertex said, and has since resolved.
Busulfan has long proved tricky for companies developing gene therapies, with the chemo regimen proving a necessary but intensive process for patients. It’s been linked in the past to cancer and some have linked it to potential cases of leukemia and myelodysplastic syndrome seen in bluebird bio’s gene therapy studies.
Additionally, as Vertex and CRISPR had previously revealed, one beta thalassemia patient experienced four serious side effects related or possibly related to CTX001. They all occurred within the context of an inflammatory response and have also resolved.
In the beta thalassemia study, investigators followed the 15 patients for a range of four to 26 months, and the sickle cell patients from five to 22 months. Seven from across both studies are more than a year out since receiving treatment. Friday’s results are an update to a data cut from December’s ASH conference, which had only included 10 patients.
The gene therapy in question, being developed jointly by Vertex and CRISPR, is an autologous ex vivo CRISPR/Cas9 treatment. Vertex teamed up with CRISPR back in 2015, but the pair expanded on their partnership in April in a bid to develop the treatment more quickly.
In the expansion, Vertex paid an additional $900 million cash to take another 10% of future sales from the gene editing therapy, with CRISPR handing over responsibility for commercializing CTX001 in the US. Along with other recent changes to their partnership, the move effectively hands Vertex responsibility for manufacturing the therapy and stewarding it past regulators across the globe.
Should CTX001 become the first CRISPR-based therapy to hit the market, that wager would give Vertex a significant sales advantage over rivals like bluebird. The Nick Leschly-run company has faced an uphill climb for its gene therapy programs, ultimately splitting itself into two companies at the beginning of the year.