Impact of pre-existing immunity on safety and biodistribution of a single AAV9 vector intrathecal injection in cynomolgus monkeys.

Adeno-associated virus (AAV) vectors are widely used for gene therapy as they deliver therapeutic genes with minimal toxicity. However, pre-existing anti-AAV immunity in a large percentage of humans poses a challenge to their efficacy and safety; only patients with low or no AAV-specific antibodies are currently eligible for systemically administered gene therapies. The impact of pre-existing anti-AAV total antibodies (TAbs) following local delivery is less characterized. This study explored the impact of pre-existing anti-AAV9 TAbs on biodistribution and safety of an AAV9 tool vector administered intrathecally to cynomolgus monkeys. Although high-serum AAV9 titers did not affect central nervous system vector biodistribution, it reduced distribution to peripheral tissues, except the spleen in which vector genome copies increased. Animals with high pre-existing antibodies had rapid and transient systemic interferon response, faster therapy-emergent antibody increases in the cerebrospinal fluid (CSF), and higher cellular responses in the spleen but no major safety concerns. Our findings suggest that using serum AAV titers as an eligibility criterion for intrathecal AAV-based gene therapy could exclude patients who might benefit from treatment. Stronger anti-vector immune responses in animals with high anti-AAV9 TAb titers suggest the need to closely monitor treatment-emergent immune responses and potential consequences for highly seropositive patients.