PROJECT SUMMARY Type 1 diabetes (T1D) is a life-threatening autoimmune disease affecting over 1 million patients in the United States that occurs when the immune system attacks and destroys insulin- producing beta islet cells in the pancreas. Treatment of T1D requires a lifetime of constant maintenance to avoid life-threatening complications. There is an urgent need for a therapy that can engineer the immune system to prevent disease progression at early stages, prevent damage to islet cells, and have a long-lasting and transformative effect on patients. One method of achieving T1D-specific tolerance is to genetically engineer antigen-presenting cells (APCs) to present disease-relevant antigen(s). Antigen presentation in the presence of tolerogenic signals can lead to the maturation of disease-specific protective regulatory T cells (Tregs). In particular, liver-resident APCs express low levels of activating co-stimulatory molecules, and surrounding cells secrete immunosuppressive signals, making the liver a tolerogenic environment. We hypothesize that non-viral transfection of APCs in the liver with genes encoding T1D-specific autoantigens will promote safe and specific protective tolerance as a tolerogenic vaccine for the prevention and treatment of autoimmune T1D. We will develop biodegradable nanoparticles to safely and effectively program immune cells in vivo, including APCs. We will first create and well-characterize the new nanobiotechnology and validate it in in vitro models (Aim 1). We will then evaluate the nanobiotechnology in vivo in mouse models of T1D (Aim 2). Finally, we will evaluate these NPs with human immune cells in vitro and in vivo, bringing this technology closer to translation (Aim 3). This nanoparticle-based biotechnology is designed to enable a safe and effective method of immune cell engineering to treat T1D.