It has previously been shown that the baculoviral cathepsin (v-cath) protease can cause degradation of VP proteins in AAVs . As the samples used in this study were produced using an Sf9 production system, which requires baculoviral infection for AAV production, it is understandable that this could be a cause for some of the fragments detected. Additionally, the immune response generated by baculoviral infection, which includes the activation of stress response and apoptosis, could contribute to the degradation of capsid proteins or their faulty production . This might also mean that the detection of the M203-VP3 protein in AAV9 is reflective of the product being harvested during a late stage of production, were most of the cells would be dying, and thus not functioning as they would when healthy. However, it is impossible to determine this within this study and further investigation is required to do so.