Systematic evaluation of BBB-penetrant AAV capsids in marmosets identifies VCAP-102 as a highly efficient brain-transducing capsid.

Recent advances in engineering adeno-associated virus (AAV) capsids capable of crossing the blood-brain barrier (BBB) have led to the development of numerous variants aimed at enhancing central nervous system gene delivery. Over the past decade, as new BBB-penetrant capsids were reported or independently identified through our own capsid library screening, we systematically evaluated their performance in adult marmosets, using a standardized experimental framework. Here, we present a cross-comparison of eleven AAV variants, predominantly AAV9-derived, alongside native AAV9 following systemic administration. Whole-brain reporter expression was quantitatively assessed using uniform imaging and analysis pipelines to enable relative comparison across animals. Under these conditions, most previously reported and newly identified BBB-penetrant variants-including those obtained through our own screening efforts-did not exhibit brain transduction levels clearly distinguishable from those of AAV9 based on whole-brain fluorescence intensity. In contrast, VCAP-102 consistently produced markedly higher brain-wide reporter expression across animals, accompanied by substantially increased vector genome copy numbers in the marmoset cortex, with most GFP-positive cells corresponding to neurons. These findings provide a systematic benchmark for evaluating BBB-penetrant AAV capsids in non-human primates and identify VCAP-102 as a highly efficient vector for systemic brain gene delivery.