Lack of germline transmission in male mice following a single intravenous administration of AAV5-hFVIII-SQ gene therapy.

Valoctocogene roxaparvovec (AAV5-hFVIII-SQ) is an adeno-associated virus serotype five gene therapy under investigation for the treatment of hemophilia A. Herein, we assessed the potential for germline transmission of AAV5-hFVIII-SQ in mice. Male B6.129S6-Rag2tm1Fwa N12 mice received a single intravenous dose of vehicle or 6 × 1013 vg/kg AAV5-hFVIII-SQ. Vehicle and AAV5-hFVIII-SQ-treated mice were mated with naïve females 4 days after dosing, when the concentration of vector genomes was expected to be at its peak in semen, and 37 days after dosing, when a full spermatogenesis cycle was estimated to be complete. Quantitative PCR was used to evaluate the presence of transgene DNA in liver and testes from F0 males dosed with AAV5-hFVIII-SQ and liver tissue of F1 offspring. Transgene DNA was detected in liver and testes of all F0 males dosed with AAV5-hFVIII-SQ, confirming successful transduction. Importantly, no transgene DNA was detected in any tested F1 offspring derived from F0 males dosed with AAV5-hFVIII-SQ. Using a novel 2-stage statistical model that takes into account the number of males dosed with AAV5-hFVIII-SQ and the number of offspring sired by these males, we estimate that the risk of germline transmission is <5% with a 99.2% confidence level.

Ultra-sensitive AAV capsid detection by immunocapture-based qPCR following factor VIII gene transfer.

Adeno-associated virus (AAV)-based gene therapy vectors are replication-incompetent and thus pose minimal risk for horizontal transmission or release into the environment. In studies with AAV5-FVIII-SQ (valoctocogene roxaparvovec), an investigational gene therapy for hemophilia A, residual vector DNA was detectable in blood, secreta, and excreta, but it remained unclear how long structurally intact AAV5 vector capsids were present. Since a comprehensive assessment of vector shedding is required by regulatory agencies, we developed a new method (termed iqPCR) that utilizes capsid-directed immunocapture followed by qPCR amplification of encapsidated DNA. The limit of detection for AAV5 vector capsids was 1.17E+04 and 2.33E+04 vg/mL in plasma and semen, respectively. Acceptable precision, accuracy, selectivity, and specificity were verified; up to 1.00E+09 vg/mL non-encapsidated vector DNA showed no interference. Anti-AAV5 antibody plasma concentrations above 141 ng/mL decreased AAV5 capsid quantification, suggesting that iqPCR mainly detects free capsids and not those complexed with antibodies. In a clinical study, AAV5-FVIII-SQ capsids were found in plasma and semen but became undetectable within nine weeks after dose administration. Hence, iqPCR monitors the presence and shedding kinetics of intact vector capsids following AAV gene therapy and informs the potential risk for horizontal transmission.