Project Summary The goal of this proposal is to increase our understanding of the therapeutic benefits of using platelets as delivery systems for disease treatments, with the long-term goal of developing platelet-based therapeutic cell treatments for metabolic diseases, specifically, lysosomal storage diseases (LSDs). LSDs are inherited metabolic diseases that are characterized by an abnormal buildup of various toxic materials in the body’s cells as a result of lysosomal enzyme deficiencies. These malfunctioning enzymes represent a group of about 50 different genetic diseases and, though individually rare, their combined prevalence is estimated to be 1 in every 8,000 births. LSDs affect different parts of the body including the skeleton, brain, skin, heart, and central nervous system. All patients with LSD have a limited life expectancy. Platelets are anucleate blood cells that circulate throughout the body and play an important role in homeostasis, wound healing, angiogenesis, inflammation, and clot formation. Platelets are naturally filled with secretory granules that store large amounts of proteins, which are formed from the cytoplasm of megakaryocytes (MKs), their precursor cells. When platelets are activated, a large number of bioactive proteins are released from their granules to participate in a myriad of physiological processes. We propose to take advantage of platelets’ innate storage, trafficking, and release capacities, to engineer them as delivery vehicles for the development of next generation delivery methods for lysosomal enzymes to treat patients with LSDs. My central vision is to engineer blood platelets to control the secretion of enzymes required for proper lysosomal function as a therapeutic treatment for patients with LSDs. I will build upon my previous work where I have developed novel genetic tools and circuits to re-engineer cells to perform specific tasks to systematically design, build, and characterize new genetic tools for packaging lysosomal enzymes into platelets. Additionally, I will rationally design receptors that are capable of activating platelets to trigger the release of enzymes upon binding to specific drugs and/or binding to tissue specific peptides. Success from this proposal will result in paradigm-shifting therapies with unprecedented levels of flexibility, precision, and personalization. The resulting engineered platelets will be the most sophisticated therapeutic agents ever developed for treating metabolic disorders. Furthermore, the genetic tools and design principles developed here will serve as a general platform that can be combined with any other treatments to complement existing therapies, thus this work will have an immediate and broad impact on many metabolic disorders.