T cells carry out their functions by specifically recognizing antigens through their T cell receptors (TCRs), making the identification of TCR specificities crucial for understanding health and disease. Over the past decade, several antigen discovery methods have been developed to deconvolute TCRs. Our laboratory has established a cell-based antigen discovery platform based on chimeric receptors termed SABRs (Signaling and Antigen-presenting Bifunctional Receptors). SABRs are extracellular peptide-MHC complexes fused to intracellular signaling domains. SABRs present a covalently linked epitope to T cells and induce a readable signal upon their recognition. Moreover, large epitope libraries in SABRs can be constructed to screen the cognate epitopes of a given TCR. The modularity and continued refinement of SABRs allow antigen discovery for CD8+ and CD4+ T cells. In this chapter, we provide an overview of the SABR platform, followed by a detailed description of the steps involved in the generation of SABR libraries and performing SABR screens to deconvolute TCR specificities.