ASH: Gene Therapy Shows Promise for Hemophilia B

Administration of virus vector expressing factor IX transgene prevents spontaneous bleeding

MONDAY, Dec. 12 (HealthDay News) -- Peripheral vein infusion of a single dose of serotype-8 pseudotyped self-complementary adeno-associated virus (AAV) vector, which expresses the codon-optimized coagulation factor IX (FIX) transgene (scAAV2/8-LP1-hFIXco), can prevent spontaneous hemorrhage in patients with severe hemophilia B (HB), according to a study published online Dec. 10 in the New England Journal of Medicine to coincide with presentation at the annual meeting of the American Society of Hematology, held from Dec. 10 to 13 in San Diego.

Amit C. Nathwani, M.B.Ch.B., Ph.D., from the University College London, and colleagues investigated a novel gene therapy approach for HB using peripheral vein infusion of scAAV2/8-LP1-hFIXco. A total of six individuals with severe HB and FIX levels of 1 percent or less were enrolled into three dose cohorts (two each in low-dose, intermediate-dose, and high-dose). The vector was administered without immunosuppression, after which participants were followed for six to 16 months.

The investigators found that, in all participants, AAV-mediated expression of FIX was seen at 2 to 11 percent of normal. Four participants discontinued prophylaxis and remained free from spontaneous bleeding. The interval between FIX prophylaxes was increased for the remaining two participants. Of the two high-dose participants, one developed asymptomatic, transient elevation of serum transaminases associated with AAV8 capsid specific T cell detection in peripheral blood. The other showed a slight increase in liver enzymes of unknown etiology. A short course of steroids in each of the high-dose participants rapidly normalized the transaminases, and maintained FIX levels in the range of 3 to 11 percent.

"Peripheral vein administration of scAAV2/8-LP1-hFIXco was well tolerated and resulted in FIX transgene expression at levels sufficient to improve the bleeding phenotype," the authors write.

Several of the study authors disclosed financial relationships with Amsterdam Molecular Therapeutics, which specializes in gene therapy.

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