AAV8-Specific Immune Adsorption Column: A Treatment Option for Patients with Pre-Existing Anti-AAV8 Neutralizing Antibodies

Background: Pre-existing neutralizing antibodies (NAbs) are a major hurdle in adeno-associated virus 8 (AAV8) gene therapy and result in patients being excluded from clinical trials. Prevalence data published by Kruzik et al. suggest that up to 50% of patients have biologically relevant NAbs against AAV8, excluding them from current clinical trials. We developed a strategy to circumvent pre-existing anti-AAV8 immunity and specifically remove anti-AAV8 antibodies.

Aim: Develop an AAV8-specific immune adsorption column (IAC) to specifically remove anti-AAV8 antibodies.

Methods: An AAV8-specific IAC was developed. Protocols were optimized to couple AAV8 capsids to activated sepharose. All procedures complied with regulatory requirements to accelerate clinical development. Accompanying mouse studies tested potential concomitant immune suppressive regimens in Bl/6 mice using AAV8-FIX vectors. NAbs were assessed using validated NAb assays of confirmed biological relevance. Titers of AAV8 binding antibodies were assessed by ELISA and T-cell responses by IFN-g ELISpot.

Results: Optimized coupling protocols revealed that AAV8 empty capsids can be linked in a stable way to resin. IAC was tested in vitro and in macaques: An IAC could be developed fitting into approved and marketed platforms for immune apheresis. By applying standard experimental procedures for apheresis column development, we showed an IAC can deplete AAV8 binding antibodies and NAbs with greater efficacy than a pan-Ig adsorber (Therasorb-IgOmni). We mimicked treatment of patients in vitro by applying different treatment cycles to plasma reservoirs and showed anti-AAV8 titers of 1:5260 could be depleted to undetectable levels in 4 to 5 treatment cycles. These data are supported by in vivo studies. The IAC is part of a strategy that uses concomitant immunosuppressants to block potential anti-AAV8 T-cell responses.

Conclusion: IAC is an enabler for treatment of patients with pre-existing immunity against AAV8 and would also facilitate re-administration. IAC is intended to be applied in combination with Takeda's AAV8 based hemophilia programs.