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Crispr Therapy Shown to Help Blood Disorder Patients

Editing DNA

(LaCasadeGoethe, Pixabay)

4 Nov. 2020. Interim clinical trial results show an experimental treatment derived from gene-edited stem cells relieves symptoms in patients with severe inherited blood diseases. The findings from two trials conducted by Vertex Pharmaceuticals Inc. and Crispr Therapeutics appear in a paper scheduled for presentation on 6 December at the American Society of Hematology annual meeting, held virtually.

Vertex Pharmaceuticals, in Cambridge, Massachusetts and Crispr Therapeutics in Zug, Switzerland are developing a treatment code-named CTX001 to correct genetic defects responsible for the inherited blood conditions sickle cell disease and beta thalassemia. CTX001 is designed to edit the patient’s own blood-forming stem cells to correct the errant genes responsible for these inherited diseases. Patients are then infused with the edited stem cells following chemotherapy pre-treatment.

Sickle cell disease is a genetic blood disorder affecting hemoglobin, a protein in blood that delivers oxygen to cells in the body. People with sickle cell disease have hemoglobin molecules that cause blood cells to form into an atypical crescent or sickle shape. That abnormal shape causes the blood cells to break down, lose flexibility, and accumulate in tiny capillaries, leading to anemia and periodic painful episodes. People with beta thalassemia have lower production of hemoglobin in their blood causing anemia, and when severe, need frequent blood transfusions.

With CTX001, blood-forming stem cells are edited with Crispr to produce high levels of healthy fetal hemoglobin, a type of protein in the blood of newborns, later replaced by adult hemoglobin. The higher levels of fetal hemoglobin from CTX001 are intended to reduce the painful sickle-cell episodes and lower the number of transfusions needed by beta thalassemia patients.

Crispr — short for clustered, regularly interspaced short palindromic repeats — makes it possible to edit genomes of organisms harnessing bacterial defense mechanisms that use RNA to identify and monitor precise locations in DNA. With CTX001, the actual editing is done by Crispr-associated protein 9, or Cas9, enzyme that programs RNA to cut DNA at precise points in genomes, making it possible to delete, insert, or correct defects in human genomes.

Vertex and Crispr Therapeutics are conducting two clinical trials, one for patients with severe sickle cell disease, and the other for beta thalassemia patients requiring frequent transfusions. Each of the early- and mid-stage trials is enrolling 45 participants, looking primarily for adverse effects and other safety indicators, but also evidence of engraftment, where blood-forming stem cells begin to make new red and white blood cells and platelets. For sickle cell patients, the study team is also looking for higher levels of fetal hemoglobin and number of painful episodes, and need for transfusions among beta thalassemia patients. There is no control or placebo group in either trial, and researchers are tracking participants for two years.

The conference paper reports on seven participants from the trials, five patients with severe beta thalassemia and two with sickle cell disease, taking part in the trials for three months or more. One beta thalassemia patient suffered hemophagocytic lymphohistiocytosis, where the body activates too many immune system cells, resulting in headaches, respiratory distress, and pneumonia in the patient. The study team says the problems were either resolved or improving at the time of the analysis. No other serious adverse effects were reported by either the beta thalassemia or sickle cell participants.

Patients in both trials quickly reported relief from their symptoms following their CTX001 infusions. All five of the beta thalassemia participants ceased their blood transfusions about one to two months after receiving CTX001. In one case, a patient has gone 15 months without needing a transfusion. And the two sickle cell patients report no painful episodes for more than a year.

In addition, participants in both trials reported engraftment of neutrophils, white blood cells in the immune system, and platelets between a median of 22 and 37 days following CTX001 infusions. And all participants reported increases in their total hemoglobin and fetal hemoglobin.

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