Bluebird Bio (BLUE) is learning that differences in the genetic mutation behind beta-thalassemia, a serious, inherited blood disease, are playing a role in how well patients respond to the company's experimental gene therapy.
Updated results from ongoing Bluebird clinical trials disclosed Thursday show six beta-thalassemia patients with genetic mutations causing drastically reduced quantities of the oxygen-carrying protein beta globin remain independent from blood transfusions following treatment with Bluebird's one-time gene therapy.
These six beta-thalassemia patients, followed for at least six months and as long as 18 months, are essentially cured (for now) by Bluebird's gene therapy, known as Lentiglobin BB305. These results extend the impressive Lentiglobin clinical benefit presented earlier this year and in 2014.
But also disclosed Thursday are updated data on three additional beta-thalassemia patients with a more severe genetic mutation rendering their beta globin entirely nonfunctional. These three patients have not been cured yet by Bluebird's gene therapy. The three patients -- all followed for at least six months -- still require blood transfusions, albeit at a reduced level from where they were before treatment with Bluebird's Lentiglobin.
"For beta-thalassemia, what we're looking at is an emergence of a genotype separation in the data," Bluebird Bio CEO Nick Leschly said in an interview.
The data are still preliminary, so no firm conclusions are being drawn, but genotypes representing approximately two-thirds of beta-thalassemia patients appear capable of achieving transfusion independence from Bluebird's gene therapy.
The remaining one-third of beta-thalassemia patients -- the "hardest clinical target," Leschly calls them -- may be looking at reduced transfusions but not independence.
A patient with severe sickle cell disease also treated with Bluebird's Lentiglobin gene therapy continues to improve and has not suffered any disease-related complications or required hospitalization, the company said.
Beta-thalassemia is caused by a missing or defective gene which prevents oxygen-carrying hemoglobin from functioning properly. Beta-thalassemia patients suffer from chronic anemia and all the patients entered into Bluebird's clinical trials had the "major" form of the disease requiring chronic blood transfusions to survive.
BlueBird's Lentiglobin replaces the defective gene with one that is fully functional. It's a one-time treatment with the ultimate goal of freeing patients from requiring chronic blood transfusions, or reducing the volume of blood transfusions.
In previous presentations of Lentiglobin clinical trial results, all beta-thalassemia patients followed for a minimum of three months achieved transfusion independence. Realistic or not, the expectation that Bluebird's gene therapy might cure all beta-thalassemia patients (and patients with sickle cell disease, too) fueled a sharp increase in Bluebird's stock price.