Phase 3 Trials of CTX001, Gene-editing Cell Therapy, Set for Children

Patricia Inácio, PhD avatar

by Patricia Inácio, PhD |

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CRISPR Therapeutics and Vertex have launched two Phase 3 trials to assess the safety and effectiveness of CTX001, an experimental gene-editing cell therapy, one in children with sickle cell disease (SCD) and another for those with transfusion-dependent beta thalassemia (TDT).

Both Phase 3 studies will enroll up to 12 children, ages 2–11. The VX21-CTX001-151 study (NCT05329649) will recruit children with severe SCD who either fail to respond to hydroxyurea or are intolerant to it, while the VX21-CTX001-141 trial (NCT05356195) is for children with TDT.

Participants will receive a single intravenous infusion of CTX001, consisting of cells collected from a patient’s bone marrow and modified to produce fetal hemoglobin, and then be followed for up to two years. Both trials are expected to finish in May 2026.

Enrollment is not yet open and study sites not yet announced; contact information is available on the trials’ webpages, here and here.

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The news follows complete enrollment for two ongoing Phase 2/3 trials testing a single dose of the investigational therapy in patients ages 12–35 with severe SCD in the CLIMB-SCD-121 study (NCT03745287), and with TDT in the CLIMB-Thal-111 study (NCT03655678).

Over 75 patients across both those trials have been dosed up to date. Preliminary results covering seven SCD patients, released last year, reported clinically meaningful increases in hemoglobin levels and no vaso-occlusive crises (VOCs); these people had been followed post-treatment for at least three months and up to nearly two years.

Positive and durable responses were also reported for TDT patients followed for at least three months in the CLIMB-Thal-111 trial.

The companies anticipate filing regulatory requests for CTX001’s approval by year’s end.

“I am pleased with the ongoing momentum across our broad portfolio of innovative gene therapy candidates and anticipate important company milestones in 2022. Alongside our partner Vertex, we remain on track to submit global regulatory filings for CTX001 in late 2022,” Samarth Kulkarni, PhD, CRISPR Therapeutics’ CEO, said in a press release.

CTX001 uses the CRISPR-Cas9 gene-editing tool to induce the production of fetal hemoglobin in blood cell precursors of patients affected either by SCD and TDT. Fetal hemoglobin is a form of hemoglobin produced during fetal development that is more effective at transporting oxygen than its adult counterpart.

Cells, once modified, are re-infused back into the patient in the form of a stem cell transplant. By boosting the levels of fetal hemoglobin, CTX001 is expected to lower the frequency of VOCs in people with SCD and the constant need for blood transfusions in TDT patients.

Patients in both trials will be asked to participate in a long-term follow-up study.