Type 1 regulatory T cells (Tr1s) are critical for regulation of autoimmunity and acceptance of hematopoietic stem cell transplants. One major limitation of Tr1 research is the lack of known master regulator, which is a transcription factor that has essential roles in both differentiation and function of the cell type. My research leverages CRISPR-Ca9-induced knockouts and in vitro Tr1 differentiation to find potential Tr1 master regulators.