A new gene therapy reduces bleeding in patients with haemophilia A, according to a clinical trial.

Haemophilia is a group of genetic conditions, predominantly affecting men and boys. Affected people do not produce a protein (Factor VIII) responsible for blood clotting, causing excessive or uncontrolled bleeding. Haemophilia A is the most common form of the disease, accounting for around eighty percent of cases.

'For people living with haemophilia A, the physical and emotional impact of needing to prevent and treat bleeding episodes through frequent IV infusions or injections cannot be underestimated,' said study leader Professor Andrew Leavitt, director of the Adult Haemophilia Treatment Centre at the University of California, San Francisco.

The effectiveness of the proposed gene therapy, Giroctocogene Fitelparvovec (GF), was examined against infusions of Factor VIII in a type of treatment known as prophylaxis, the standard treatment for Haemophilia A. The study is part of a Phase 3 trial examining whether the proposed gene therapy, developed by Pfizer and Sangamo Therapeutics, is as effective or better than a standard approved treatment for a disease.

GF comprises a protective shell, like that of a virus particle, which protects the genetic material within it, and helps it enter the patient's cells. Inside is a copy of the human coagulation Factor VIII gene – with some unnecessary parts removed – which can integrate into the target cells' DNA, and produce Factor VIII to aid blood clotting.

The study featured 75 male participants with moderately severe to severe forms of Haemophilia A, and fifty of those were monitored for six months. Results showed that over 80 percent of study participants had increased levels of Factor VIII by above five percent following one dose of GF, while more than fifty percent of participants showed increased levels of more than fifteen percent of GF after one dose.

In addition, participants demonstrated decreased annualised bleeding rates, occurrences of an extended period of bleeding recorded over a given period, decreasing from 4.73 measured before a single GF administration to 1.24 measured from week 12 to at least 15 months.

The study may continue monitoring the participants for five to fifteen years.

The trials for GF had previously been paused by the US Food and Drug Administration (FDA) after high levels of Factor VIII were observed in study participants, close to the maximum recommended limit.

The news of these findings about GF comes after the FDA approved Roctavian, another gene therapy for Haemophilia A (see BioNews 1197).