CD8+ T cells recognize and eliminate tumors in an antigen-specific manner. Despite progress in characterizing the antitumor T cell repertoire and function, identifying their target antigens remains a challenge. Here, we describe the use of chimeric receptors called Signaling and Antigen-presenting Bifunctional Receptors (SABRs) in a novel cell-based platform for T Cell Receptor (TCR) antigen discovery. SABRs present an extracellular peptide-MHC complex and induce intracellular signaling via a TCR-like signal upon binding with a cognate TCR. We devised a strategy for antigen discovery using SABR libraries to screen thousands of antigenic epitopes. We validated this platform by identifying the targets recognized by public TCRs of known specificities. Moreover, we extended this approach for personalized neoantigen discovery. The antigen discovery platform reported here will provide a scalable and versatile way to develop novel targets for immunotherapy.

T cell receptor (TCR) ligand discovery is essential for understanding and manipulating immune responses to tumors. We developed a cell-based selection platform for TCR ligand discovery that exploits a membrane transfer phenomenon called trogocytosis. We discovered that T cell membrane proteins are transferred specifically to target cells that present cognate peptide-major histocompatibility complex (MHC) molecules. Co-incubation of T cells expressing an orphan TCR with target cells collectively presenting a library of peptide-MHCs led to specific labeling of cognate target cells, enabling isolation of these target cells and sequencing of the cognate TCR ligand. We validated this method for two clinically employed TCRs and further used the platform to identify the cognate neoepitope for a subject-derived neoantigen-specific TCR. Thus, target cell trogocytosis is a robust tool for TCR ligand discovery that will be useful for studying basic tumor immunology and identifying new targets for immunotherapy.

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T cell receptor mediated immunotherapy using engineered Hematopoietic Stem/Progenitor Cells leads to durable partial suppression of HIV in humanized mice. Sustained viral suppression is accompanied by viral evolution under selection pressure. This study highlights the potential for TCR immunotherapy and the need to target multiple epitopes. Abstract:Effective CD8+ T cell responses targeted to the KK10 epitope of HIV presented by HLA-B*27:05, a protective HLA allele, correlate with the ability to control infection without antiretroviral therapy (ART). Here, we report an immunotherapy approach using two B*27:05-KK10-specific T Cell Receptors (TCRs) isolated from HIV controllers. Immunocompromised mice engrafted with human Hematopoietic Stem/Progenitor Cells (HSPCs) encoding for the TCRs showed differentiation into functionally active engineered T cells. Following infection with HIV, both TCRs showed sustained, albeit modest, viral suppression over 32 weeks, accompanied by a concomitant increase in CD4+ T cells. Sequencing of viral quasi-species from the plasma of infected mice demonstrated clear evidence for viral evolution under selection pressure from the TCRs. The most commonly observed mutation in the KK10 epitope was L6M, which preserved viral fitness but showed attenuated recognition by the TCRs. These studies show that TCR-immunotherapy was able to suppress HIV infection long-term while driving HIV evolution in humanized mice. Introduction: