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FDA Delays Crispr Trial for Inherited Blood Diseases

Crispr-Cas9 illustration

Crispr-Cas9 illustration (

31 May 2018. The U.S. Food and Drug Administration put a hold on beginning a clinical trial of the emerging genome editing technique known as Crispr to treat inherited blood disorders. FDA’s action was reported yesterday by Crispr Therapeutics in Cambridge, Massachusetts and Vertex Pharmaceuticals Inc. in Boston, the companies planning the study.

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. The actual editing is done most often by the Crispr-associated protein 9, or Cas9, enzyme that programs RNA to silence genes and provide immunity against invading genetic material. Cas9 also harnesses RNA to cut DNA at precise points in genomes, making it possible to delete, insert, or correct defects in human genomes.

Crispr Therapeutics and Vertex are developing a treatment, code-named CTX001, adapting Crispr for the inherited blood disorders sickle cell disease and beta-thalassemia. 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.

CTX001, say the companies, is designed to treat these disorders with a patient’s own blood-forming stem cells. The stem cells are edited with Crispr to produce high levels of healthy fetal hemoglobin, a type of the 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 Therapeutics and Vertex formed their alliance in October 2015 to develop gene-editing treatments for cystic fibrosis and inherited blood disorders. As reported in Science & Enterprise, Vertex has an exclusive license from Crispr Therapeutics to develop up to 6 treatments for these diseases, as well as other genetic conditions later on. Among the scientific founders of Crispr Therapeutics is Emmanuelle Charpentier, a pioneer in genome editing with Crispr and Cas9.

In December 2017, Crispr Therapeutics and Vertex agreed to move ahead with clinical trials for CTX001, beginning with combined early- and intermediate stage studies in the U.S. and Europe. In April, the companies filed an investigational new drug application with FDA for CTX001, which authorizes clinical trials of experimental therapies. FDA yesterday returned a number of questions about the trial, which the companies say they plan to resolve quickly. Plans for an early- and intermediate-stage trial of CTX001 in Europe among beta-thalassemia patients are continuing.

Also as reported in Science & Enterprise earlier this month, FDA approved an investigational new drug application from Bioverativ, a division of drug-maker Sanofi and Sangamo Therapeutics, for early- and intermediate-stage clinical trials of genome editing to treat sickle cell disease. That therapy, however, uses zinc-finger nucleases, an earlier form of genome editing.

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