The order applies to the entirety of new and, possibly, ongoing research grant dollars that go to universities and academic medical centers.

Adeno-associated virus (AAV) gene therapies have achieved clinical success, with multiple products reaching regulatory approval. Encapsulation of AAV vectors within engineered extracellular vesicles (EVs) is an emerging strategy which could help overcome challenges including pre-existing anti-capsid immunity and the need for controlling targeting and tropism. To guide the development of EV-AAV technologies, we developed an assay for quantifying and controlling for the contribution of pseudotransduction to evaluations of EV-AAV-mediated gene delivery. We developed an AAV vector that switches its transgene output from one reporter to another when acted upon by Cre recombinase expressed in a recipient cell. Using this platform, we investigated EV-AAV transduction as a function of various engineered EV surface modifications. For actively endocytic cells (HEK293FTs), modifications that enhance EV uptake and membrane fusion influence protein delivery but not gene delivery. Conversely, in less endocytic Jurkat T cells, modifications enhancing EV uptake improved both protein and gene delivery. These conclusions held across multiple AAV serotypes. Our results resolve apparent conflicts in prior reports and suggest that effects of enhancing uptake and membrane fusion of EV-AAV vectors are recipient cell type specific. The methods developed here unambiguously dissect EV-AAV transduction mechanisms and can guide future bioengineering of EV-AAV vectors. ### Competing Interest Statement J.N.L., D.M.S. and H.I.E. have financial interests in Syenex Inc., which could potentially benefit from the outcomes of this research. National Institute of General Medical Sciences, T32GM008449 National Science Foundation, DGE-1842165, ECCS-2025633, DMR-2308691 National Cancer Institute, CA060553

Waste wood scraps, changed at the molecular level, could become heavy-duty building materials—and even replace plastic, aluminum and carbon fiber in our vehicles and gadgets.