Fecal AAV8 shedding and co-housing reduces EAE disease severity: implications for preclinical study design

Adeno-Associated virus (AAV) vectors have become an invaluable tool in research and the clinic. Likewise, AAV is used in various animal models for investigating a host of diseases. However, AAV shedding, or the release of AAV particles from the body, remains an understudied field which could be detrimental to researchers and be a potential contributor to pre-clinical variability. To our knowledge, no studies have been performed to evaluate any relationship between AAV shed particles and the effects these particles may have on cage mates. As such, we evaluated the level of AAV viral genomes in the fecal matter of C57BL6/J mice following the intravenous administration of AAV8. Here we show that AAV genomes are shed from female C57BL/6J mice for a minimum of 2 months following intravenously injected AAV8 vector. We also sought to determine if these shed AAV particles could affect non-vectored cage mates in experimental autoimmune encephalomyelitis (EAE), an animal model for multiple sclerosis (MS). We found an association between caging vectored animals with non-vectored animals and a reduction in disease severity in the non-vectored animals. We also found an association between disease severity and the ratio of vectored:non-vectored animals in the cage. Our findings should act as a word of caution to researchers performing AAV studies and should be considered to prevent confounding variables and bias in results.