Recent hemophilia B clinical trials using adeno-associated virus (AAV) gene delivery have demonstrated much lower coagulation factor IX (FIX) production in patients compared with the high levels observed in animal models and AAV capsid-specific cytotoxic T lymphocyte response elicited at high doses of AAV vectors.
Multiple independent adeno-associated virus (AAV) gene therapy clinical trials for hemophilia B, utilizing different AAV serotypes, have reported a vector dose-dependent loss of circulating factor IX (FIX) protein associated with capsid-specific CD8<sup>+</sup> T cell (Cap-CD8) elimination of transduced hepatocytes.
In conclusion, the present study demonstrated that the exogenous gene hFIX was effectively expressed following site‑specific targeting into the AAVS1 locus in MSCs; therefore, MSCs may be used as potential cell carriers for gene therapy of hemophilia B.
In this article we review the current state of AAV mediated gene therapy for hemophilia B in the clinic, detail progress since the first successful trial, and discuss alternative approaches from the AAV gene therapy field.
Vector capsid dose-dependent inflammation of transduced liver has limited the ability of adeno-associated virus (AAV) factor IX (FIX) gene therapy vectors to reliably convert severe to mild hemophilia B in human clinical trials.
These impressive results prompted initiation of two Phase I/II clinical trials to evaluate the safety of AAV-factor IX gene transfer to muscle and liver of patients with severe hemophilia B. Herein, we have reviewed results from studies in animals with hemophilia, early experience with the vector system in the clinic, recent innovative approaches in vector design and delivery, and strategies to circumvent immunological limitations.
In a staged approach, AAV-factor IX (AAV-F.IX) was first administered at doses of up to 1.8 x 10(12) vector genomes/kg (vg/kg) into the skeletal muscles of men with hemophilia B.