Project Summary and Abstract Gene therapy enables the treatment of a large number of genetic diseases through delivery of nucleic acids striking at the root of the disease. This is advantageous because it is highly modular, allowing for a number of different cargo nucleic acids to be delivered depending on the disease cause. As such, the ideal gene therapy delivery vector would be able to carry a variety of cargo, deliver this in a targeted manner, and accommodate a range of cargo sizes. There are a number of techniques utilized to deliver nucleic acids including viral systems like adenovirus, adeno-associated virus (AAV), and lentivirus, as well as non-viral methods including nanoparticles. Although these therapies can be successful, a key limitation to currently used vectors is the immune response which can lead to ineffective delivery of nucleic acid cargo. There is currently a need to develop effective and non-immunogenic delivery vehicles for gene therapy for a wide range of diseases, including neurological disease, for which effective delivery vehicles have yet to be designed. To this end, mammalian genomes contain numerous virus-like genes, some of which have been co-opted by their host cells for important functions. Among these are homologs of gag, which encodes the capsid protein. We hypothesize that endogenous genes encoding a capsid domain have the ability to self-assemble into capsids and mediate intercellular communication by binding, secreting, and delivering nucleic acid cargos. We propose to explore and re-engineer endogenous capsid-containing proteins for use as gene therapy vectors. We hypothesize that delivery vehicles composed entirely of self proteins will be more effective than standard vectors as they could be non-immunogenic. Here we propose to use an approach combining in vitro characterization, re-engineering, and in vitro and in vivo validation to identify candidate proteins and learn how they can be re-engineered. These systems will ideally be modular, having both programmable cargo and tropism to treat a range of diseases. We hope that by identifying and re-engineering these systems, the resulting fully endogenous delivery vehicle will be useful for efficient, reprogrammable, and non-immunogenic gene delivery. With the goal of becoming an independent investigator, this project will also support development of computational biology skills, molecular biology expertise as well as mentorship and scientific communication skills. These will be supported by the excellent research environment at the Broad Institute and MIT.