Sigilon Therapeutics has received notification from the US Food and Drug Administration (FDA) about a clinical hold on its Phase I/II clinical trial of SIG-001 to treat severe or moderately severe haemophilia A.

The notification comes after the company submitted a serious adverse event (SAE) and temporary suspension of patient enrolment to the FDA and other regulatory authorities.

SIG-001 is being developed to continuously secrete human FVIII for preventing bleeding episodes in patients with severe or moderately severe haemophilia A.

The open-label, dose-escalation Phase I/II trial commenced last year to assess the safety, tolerability and efficacy of the drug candidate in adult patients. It is expected to complete in 2026.

Three participants have so far received SIG-001 dosing.

The third patient was given the highest SIG-001 dose and developed inhibitors to Factor VIII (FVIII), which is a known complication of FVIII treatment.

Sigilon noted that the patient is having a good response to medical therapy and his condition is improving.

The FDA has asked the company to provide additional data on factors that could lead to the development of inhibitors in this patient, including family history and immune stimulation due to a recent vaccine, among other information.

According to the trial protocol, all three haemophilia patients will be followed up and the company will keep investigating the SAE.

Sigilon Therapeutics president and CEO Rogerio Vivaldi said: “Patient safety is our top priority, and we are encouraged that the patient is recovering.

“In collaboration with the regulatory agencies and our advisers, we are conducting a thorough investigation of this event to confirm whether there was a causal relationship between the development of inhibitors and SIG-001.”

The Safety Review Committee for SIG-001 will analyse the SAE investigation status while the company will submit additional information upon availability.