Mapping of Pre-Existing Humoral Immunity to AAV and Natural AAV Capsid Presence in Human Tissues: Observations from a Polish Surgical Cohort

Vectors based on adeno-associated viruses (AAVs) are widely used as a delivery system in gene therapy. However, preexisting immunity against AAV remains a major limitation. This study examines the prevalence of AAV genomes and anti-AAV2 immunity in a Polish cohort of adult patients undergoing planned surgical interventions, which serves as a random sample of the general Polish population. The presence of AAV capsid sequences was analyzed in tissue samples using PCR and endogenous AAVs were detected in 33.95% of samples. Anti-AAV2 IgG antibodies were measured by a single point ELISA and were present in 80.93% of patients. Neutralizing activity was evaluated using an AAV2 transduction inhibition assay in HEK293T cells, revealing a 60% reduction in functional activity by patients’ sera. Tissue AAV PCR-positivity was associated with stronger neutralizing activity although the correlation with seropositivity was not as strong. These results suggest that pre-existing humoral immunity against AAV is common in the Polish adult population, indicating frequent exposure to naturally occurring AAVs. The findings provide important data on pre-existing anti-AAV immunity—a key factor considered in clinical trials and gene therapy development. Furthermore, the identification of naturally occurring AAV variants in human tissues points to the potential use of new sources of capsids with potentially distinct biological properties, which could contribute to the advancement of gene therapies.