Capsida Biotherapeutics has suspended its clinical trial of an experimental gene therapy after the first participant died following treatment, marking another setback for the gene therapy field amid growing safety concerns.
The biotechnology company disclosed the death in a letter Wednesday to the patient community for STXBP1-related disorders, the rare neurodevelopmental disease its gene therapy CAP-002 is designed to treat. Capsida noted it has informed the Food and Drug Administration and will soon provide regulators a full report of the patient's death.
"We understand this devastating news will raise questions and uncertainty, and we are working with urgency to gather information and find answers," Capsida wrote in its letter to the community.
Trial Details and Patient Population
Capsida received FDA approval to begin its clinical trial just four months ago in May. The company aimed to enroll around 12 children with STXBP1-related disorders into its trial, which had opened recruitment at Weill Cornell Medicine in New York and the Children's Hospital of Philadelphia in Pennsylvania.
People with STXBP1-related disorders usually experience seizures beginning in their first year of life. Symptoms can range wider, including development delays, decreased muscle tone, and difficulty walking and speaking. There is also a risk of sudden death in epilepsy. Typically, children diagnosed with the condition are treated with anti-seizure medicines to control their convulsions.
Therapeutic Approach and Technology
CAP-002 uses a specially engineered virus to reach the brain and aims to make up for deficient levels of a vital protein encoded by the STXBP1 gene that helps pass messages between nerves. The company needed to custom design its viral vector, as the types of naturally occurring viruses gene therapy developers typically co-opt for their therapies' delivery don't adequately saturate brain neurons.
The therapy is designed to treat developmental and epileptic encephalopathy related to mutations in the syntaxin-binding protein 1, or STXBP1, gene.
Safety Investigation Underway
Capsida shared few specifics about the death, noting that it is working to understand the "root cause" of the patient's death. It remains unclear whether Capsida's treatment was directly to blame for the fatality.
"We are committed to keeping the community informed about what happened and our plans for the program as soon as we have information to share," Capsida wrote in its letter.
The STXBP1 Foundation, a nonprofit patient advocacy group, added in a separate community note: "While we do not have ... answers yet, we are in close contact with the study sponsor and investigators and will share verified updates as the formal safety review progresses."
Broader Gene Therapy Safety Concerns
The news follows patient deaths over the past year in clinical trials of gene therapies for two types of muscular dystrophy and a rare neurological disorder, and will therefore likely draw significant scrutiny from regulators and the medical community.
Company's Broader Pipeline
Capsida is also developing gene therapies for Parkinson's disease and Friedreich's ataxia. The former program was cleared in June to begin human testing, but it's not clear whether any patients have been treated yet.
