Table 1.

Session 1: Control of level and location

Topic	Needed knowledge and strategies
Addressing overexpression	Advance methods and technologies that will result in desired intracellular concentrations of AAV or ASOs across the CNS or to targeted cell types.
	Understand the natural expression of the gene of interest in the context of lifespan and in the right intracellular environment (cell autonomous), particularly for neurodevelopmental disorders.
Developing cell- and organ-specific capsids	Develop AAV capsids that will (1) transduce specific CNS cell types, including different neuronal and glial cell subtypes; (2) transduce the various neuronal and glial progenitor cells at different stages of CNS development; and (3) de-target specific cell types or organs that contribute to an immune response or toxicity when they are transduced.
	Develop accessible methods to determine whether AAV capsids identified by rational design or directed evolution in animal models translate to cell- and organ-specific expression in humans.
	Explore other viral vector delivery options including lentivirus, nonpathogenic herpes virus, rabies, measles, and other RNA and DNA viruses or non-viral delivery methods such as liquid nanoparticles.
Developing regulatable vectors: Promoters/enhancers	Develop new cell type-specific promoters/enhancers in combination with AAV capsids (and potentially miRNAs) that will express the transgene in specific CNS cell types, including the different types of neurons as well as glia, and result in the appropriate expression levels in the correct cell type.
	For neurodevelopmental disorders, design regulatable or spatiotemporal promoters/enhancers that mimic the endogenous expression levels in the correct cell type throughout neurodevelopment.
	Understand how the cis elements (e.g., ITRs) from viral vectors are contributing to the promoter/enhancer activity and whether ITRs can be insulated to prevent interaction with the promoter/enhancer.
	Examine other factors that may influence transgene expression, including sex differences, circadian rhythm differences, and environmental factors.
AAV CNS atlas for cell specificity and biodistribution	Produce a public resource that includes data on both cell specificity and biodistribution for the various AAV vectors, including the capsid, promoter/enhancer, transgene, and miRNA combinations; in addition, it should integrate data on the methods/processes of rAAV production and capture the vector quality, including the full/empty capsid ratio.
	Multiple variables should be considered, including species, age, sex, and environmental factors; the data could include advances in imaging modalities, single cell expression, and post-mortem analysis.
Off-target effects and toxicity	Investigate the mechanisms and determinants of AAV integration into the host genome.
	Understand the long-term effects in patients of CNS-directed AAV gene-targeted therapy, including AAV integration.