26 April 2019

A genetic therapy for haemophilia which involves producing Factor VIIa could be used prophylactically to prevent bleeding episodes in hard-to-treat patients, US researchers have reported.

The therapy has so far been tested in a rat model of haemophilia A, and uses a viral vector to deliver the rat F7 gene. This enabled researchers to determine the optimum levels of Factor VIIa for effective prevention of bleeds.

Dr Paris Margaritis of Children's Hospital of Philadelphia, USA, and colleagues developed the treatment to help patients who develop inhibitor antibodies to the standard factor replacement therapy.

Dr Margaritis said: “Patients who develop antibodies to the coagulation factors have a complicated treatment. A different factor, called coagulation factor VIIa, restores blood clotting when given after a bleed occurs, but we don't know the target level of that would prevent bleeds before they start.

The study showed that transgenic expression of Factor VIIa at a certain level reduced spontaneous bleeding episodes - and at a greater level eliminated them entirely. In addition, in an injury model, transgenic expression of Factor VIIa also reduced blood loss in the rats.

Commenting on the study, Dr Margaritis said: “For the first time, we have threshold levels of factor VIIa for prophylactic use.

“Because factor VIIa bypasses the need for factor VIII or IX, it should work in both haemophilia A and haemophilia B. Furthermore, it works whether or not [inhibitor antibodies] are present in the blood.”

The research, which was published in the journal Blood Advances, offers the first target levels for ‘bypass agent’ prophylaxis. However, more work is needed to validate the findings before they can be translated into future human trials.

Source: Zintner, S.M., Small, J.C., Pavani, G., Dankner, L., Marcos-Contreras, O.A., Gimotty, P.A., Kjelgaard-Hansen, M., Wiinberg, B., & Margaritis, P. (2019) “Gene-based FVIIa prophylaxis modulates the spontaneous bleeding phenotype of hemophilia A rats”, Blood Advances, available from doi: 10.1182/bloodadvances.2018027219


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