SPK-9001 is an experimental gene therapy for hemophilia B being developed by Spark Therapeutics in collaboration with Pfizer.

Patients with hemophilia B lack a blood clotting factor called factor IX; SPK-9001 is designed to correct this deficiency.

The U.S. Food and Drug Administration (FDA) granted SPK-9001 breakthrough therapy designation in July 2016, which permits its speedy development and FDA review. The European Medicines Agency (EMA) included SPK-9001 in its priority medicines (PRIME) program, which is  designed to proactively support the development of therapeutics for rare disorders with unmet medical needs.

SPK-9001 also is known as PF-06838435, SPK-FIX, C0371005, and fidanacogene elaparvovec.

How SPK-9001 works

Hemophilia B is caused by a mutation in the gene that carries the instruction to produce clotting factor IX, a protein that helps in the normal clotting of blood.

SPK-9001 is a gene therapy candidate designed to deliver a healthy copy of the gene encoding for factor IX to the patient’s liver cells where the clotting factors are made. SPK-9001 uses a genetically modified, harmless adeno-associated virus (AAV) to deliver the gene to the body. Once delivered to the liver cells, SPK-9001 helps maintain a constant and sustained level of factor IX in the blood of hemophilia B patients.

SPK-9001 in clinical trials

A multinational Phase 1/2 open-label study (NCT02484092) is evaluating the safety and pharmacokinetics (movement through the body) of a single dose of SPK-9001 in 15 men with hemophilia B, ages 18 and older. According to  results from 2018, five to 121 weeks after treatment, all treated patients showed a significant reduction in bleeding and 99% of them stopped taking factor IX infusions. No serious adverse side effects from the treatment were reported.

In an ongoing Phase 2 observational study (NCT03307980), a total of 20 male hemophilia B patients who have been treated previously with SPK-9001 are being monitored for five years. These patients, age 18 and older, will be observed for the long-term safety and clinical outcome of the treatment. The durability of SPK-9001 to provide sustained levels of factor IX for more than five years also will be assessed. The trial is recruiting participants in the U.S. and Australia.

A Phase 3 trial is recruiting participants worldwide to assess the safety and effectiveness of SPK-9001 in hemophilia B patients. The first part of the study, a lead-in Phase 3 trial (NCT03587116) will investigate the effectiveness of the current standard of care factor IX replacement therapy taken by patients in their usual care setting. Their bleeding rates, adverse reactions, and other pertinent events will be evaluated for six months. No SPK-9001 will be administered in this part of the study. A total of 110 male patients, ages 18 to 64, will be enrolled for this part of the study. Data collected will serve as a control for the next part of the study in which SPK-9001 treatment will be evaluated.

Other information

The immune system of some patients may recognize the AAV vector in SPK-9001 as foreign and mount a response to degrade it. Delivering the treatment through the bloodstream could worsen the immune reaction. Because of that, researchers have assessed whether gene therapy can be administered through the muscles.

In a dog model of hemophilia B, AAV vector containing the do factor IX gene was injected once into the muscle on one of the animals’ legs. Within 150 days of treatment, levels of dog factor IX protein (also called factor IX-Padua)  increased by 54–85%. At the six-year follow-up, no bleeding event was noted. The treatment was well-tolerated without any adverse side effects, and no immune reaction was detected, suggesting a viable alternate route for administering the therapy.


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