Gene transfer for hemophilia B shows progress
SAN DIEGO—Researchers say they have optimized the SPK-9001 adeno-associated viral (AAV) vector
so that a “simple infusion” has significantly reduced bleeding events and the need for regular factor IX (FIX) infusions in 9 hemophilia B patients.
Eight of the patients were able to stop receiving FIX infusions and achieved an annualized bleeding rate (ABR) of 0. One patient had an ABR of 2 and required on-demand FIX therapy.
Lindsey George, MD, of the University of Pennsylvania in Philadelphia, presented these data, updating the interim results from the phase 1/2 trial of SPK-9001, during the plenary session of the 2016 ASH Annual Meeting (abstract 3*).
The trial is sponsored by Spark Therapeutics in collaboration with Pfizer.
Dr George explained that the bulk of hemophilia gene transfer efforts have coalesced around the use of in vitro, liver-directed, recombinant AAV vectors.
Earlier data showed sustained FIX activity at approximately 5% with AAV-serotype 8 (AAV8) vectors at 2 x 1012 vg/kg. However, levels of FIX:C at 12% are necessary to avoid bleeding into the joints, and higher doses elicit a capsid immune response.
Therefore, the team hypothesized that a highly efficient vector capsid and expression cassette, administered at low doses, would increase FIX expression to therapeutic levels and minimize the risk of a capsid immune response.
They developed an AAV capsid (Spark100) with a liver promoter and an expression cassette consisting of a codon-optimized, single-strand transgene encoding FIX-Padua.
In a prior AAV liver-directed gene transfer clinical trial, no patient developed inhibitors.
So the team conducted a phase 1/2 trial in males age 18 and older who had FIX:C levels of 2% or less.
The patients had to have less than 1:5 neutralizing antibodies to Spark100, more than 50 factor exposure days, no prior history of FIX inhibitors, no active hepatitis B or C virus, and liver fibrosis of stage 2 or less. They had to have a negative HIV viral load with CD4 levels of 200/mm3 or more.
At baseline, patients had to be on prophylaxis or be receiving on-demand therapy and have 4 or more bleeding events the year prior to infusion or a history of hemophilic arthropathy.
Results
The researchers enrolled 9 participants, ages 18 to 52. Six patients were on prophylaxis, and 3 had on-demand therapy at baseline.
They received a 1-hour, outpatient, intravenous infusion of SPK-9001 at 5 x 1011 vg/kg and were followed up for 52 weeks, with a long-term follow-up of 14 years.
Five patients had a history of HCV, and 1 had a history of HIV and was maintained on antiretroviral therapy.
One patient had neutralizing antibody titers to Spark100 capsid at a 1:1 ratio.
Prior to receiving SPK-9001, the patients required an annual number of infusions ranging from 0 to 159. Three patients had ABRs of 0, but the remaining patients had ABRs of 1, 2, 4, 10, 12, and 49.
After receiving SPK-9001, 8 of the patients were able to stop receiving FIX infusions and
achieved an ABR of 0. One patient had an ABR of 2 and required on-demand FIX therapy.
Dr George described one patient, a 23-year-old male who had severe hemophilia B and was maintained on weekly rFIX-Fc prophylaxis. He had no history of HCV or HIV.
Prior to receiving SPK-9001, he had 98 infusions and 4 breakthrough bleeds. After SPK-9001, he had a FIX activity level of 33% of normal at 52 weeks, no bleeding episodes, and required no rescue factor.
He had no vector-related adverse events, required no immunosuppression, and was safely off prophylaxis.
