AAV9 transduction mediated by systemic delivery of vector via retro-orbital injection in newborn, neonatal and juvenile mice

Adeno-associated virus (AAV)-based gene therapy is gaining popularity owing to its excellent safety profile and effective therapeutic outcomes in a number of diseases. Intravenous (IV) injection of AAV into the tail vein, facial vein and retro-orbital (RO) venous sinus have all been useful strategies to infuse the viral vector systemically. However, tail vein injection is technically challenging in juvenile mice, and injection at young ages (≤ postnatal day-(P)21) is essentially impossible. The temporal or facial vein is localized anterior to the ear bud and is markedly visible in the first couple of days postnatally. However, this method is age-dependent and requires a dissecting microscope. Retro-orbital injection (ROI), on the other hand, is suitable for all murine ages, including newborn and older mice, and is relatively less stressful to animals compared to tail vein injection. Although many reports have shown ROI as an effective route of AAV delivery, herein we aim to highlight and summarize the methods and benefits of ROI. To capture the full spectrum of transduction efficiency mediated by ROI, we transduced the editing-dependent reporter mice (Ai9 Cre reporter mice) with the AAV9 vector, which targets a wide range of peripheral tissues with exceptional brain tropism. We also provide a comprehensive description of the ROI technique to facilitate viral vector administration without complications.