The human parvovirus adeno-associated virus (AAV) has been developed into a powerful in vivo vector as exemplified by the AAV9 gene therapy Zolgensma to treat spinal muscular atrophy. Some patients, however, are precluded from treatment due to pre-existing anti-AAV immunity induced by prior exposure to endemic virus, commonly AAV2. We seek to overcome this challenge and to this end have developed a pipeline for isolation of anti-AAV human monoclonal antibodies (mAbs). We have successfully recovered the single largest panel of anti-AAV9 mAbs from Zolgensma-treated infants (n=35, Logan et al. 2023, Molecular Therapy) with the mAbs now serving as invaluable research tools for dissecting AAV biology and host-capsid interactions.
AAV infection is regarded as non-pathogenic. However, AAV2 infection has been strongly implicated in a recent global outbreak of hepatitis of unknown origin. This was first reported in the United Kingdom in 2022 and, within months, 1010 probable cases were reported in over 35 countries. Patients showed elevated transaminases (AST or ALT >500 U/L) and were <10 years of age with no previously known aetiology. Of these cases, 5% (46) required liver transplantation and 2% (22) died. These clinical findings have important implications for patient care as well as gene therapy.
We are investigating antibody responses in three children who presented with acute hepatitis at the Children’s Hospital at Westmead, Sydney (2022-23). In addition to the features described above, patients showed high anti-AAV2 IgG endpoint titres (400,000-1,600,000) compared to 50 healthy adults (<12,150). Of the switched memory B cells in patient blood samples, 0.39-0.87% secreted anti-AAV2 IgG in an in vitro culture system. Six anti-AAV2 mAbs have been recovered to date (binding affinities ranging from 2-16nM), with one cross-reactive to AAV1, AAV3B, AAV6 and AAV9. Efforts are ongoing to isolate more and to characterize their neutralising capacity and binding sites by cryo-EM.