Pharmacokinetic analysis identifies a factor VIII immunogenicity threshold after AAV gene therapy in hemophilia A mice

Abstract

Advances in the development of novel treatment options for hemophilia A are prevalent. However, the anti-FVIII neutralizing antibody (inhibitor) response to existing FVIII products remains a major treatment challenge. While some novel products are designed to function in the presence of inhibitors, they do not specific address the immunogenicity risk or mechanistic causes of inhibitor development, which remain unclear. Furthermore, most preclinical studies supporting clinical gene therapy programs have reported immunogenicity signals in animal models, especially at higher vector doses and sometimes using multiple vector designs. In these settings, immunogenicity risk factor determination, comparative immunogenicity of competing vector designs, and the potential for obtaining meaningful prognostic data remain relatively unexplored. Additionally, there remains the opportunity to investigate clinical gene therapy as an alternative to standard immune tolerance induction therapy. The current study was designed to address these issues through longitudinal dose-response evaluation of four AAV vector candidates encoding two different FVIII transgenes in a murine model of hemophilia A. Plasma FVIII activity and anti-FVIII antibody data were used to generate a pharmacokinetic model that 1) identifies initial FVIII expression kinetics as the dominant risk factor for inhibitor development, 2) predicts a therapeutic window where immune tolerance is achieved, and 3) demonstrates evidence of gene therapy-based immune tolerance induction. While there are known limitations to the predictive value of preclinical immunogenicity testing, these studies can uncover or support the development of design principles that can guide the development of safe and effective genetic medicines.

Overcoming Hemophilia A Gene Therapy Limitations with an Enhanced Function Factor VIII Variant

“…5d ). Consistent with prior work 25,48,49 , studies in immune-competent HA/C57BL/6 mice challenged with recombinant FVIII ( Extended Data Fig. 4 a-c) or AAV-mediated FVIII expression ( Extended Data Fig.…”

“…These experiments were also designed to assess if there were any differences in longitudinal pharmacokinetics of FVIII-WT and FVIII-QQ expression. HA/CD4KO mice were used because immune- competent C57BL/6 mice mount a robust antibody response to human FVIII expression 25 . Animals were assigned to the mild HA (0.05 to <0.4 nM), normal (0.4 to <1.5 nM) and elevated FVIII (>1.5 to 3 nM) cohorts based on their steady-state week 8 plasma FVIII antigen ( Fig.…”

Hemophilic Arthropathy: Barriers to Early Diagnosis and Management

“…Despite the limitations of the predictive value of preclinical immunogenicity testing, progress has been made in developing the principles of safe and effective genetic drug design in animal models. 73 In June 2022, the European Medicines Agency has recommended granting a conditional marketing authorization in the European Union for roxaparvovec valoctocogene gene therapy for the treatment of severe hemophilia A in adults who do not have factor VIII inhibitors or antibodies against adeno-associated virus serotype 5 (AAV5). Several clinical trials are currently investigating the safety and efficacy of gene therapy in hemophilia A (NCT05454774) and hemophilia B (NCT05203679).…”