Adoptive cell transfer (ACT) is a personalized form of immunotherapy in which patient-derived tumor infiltrating lymphocytes (TILs) are expanded ex vivo and reinfused into the patient. TIL abundance currently limits broader clinical application of ACT. Peripheral blood lymphocytes (PBLs) engineered to express T-cell receptors (TCRs) selective for tumor neoantigens hold the potential of providing a more abundant source of anti-tumor T cells. However, identification of neoantigen-reactive TCRs suitable for use in ACT can be constrained by the repertoire of neoantigen-specific TCRs in patient peripheral blood or the requirement to match neoantigen-specific TCRs obtained from healthy donor PBLs with patient-specific HLA alleles. Michelle Krogsgaard, Jeff Boeke, and Jeffrey Weber from New York University School of Medicine aim to address these issues by engineering a humanized MHC/TCR/coreceptor transgenic (MTC) mouse. The MTC mouse will contain the entire human TCRα/β loci, CD8α/β, β2M and seven HLA alleles enabling generation of a TCR repertoire with significant diversity that provides reasonable HLA coverage across multiple ethnic groups. This in vivo platform will provide a robust system to screen a diverse T cell population, with broad MHC restriction, for reactivity against tumor neoantigens. The first proof of concept screen will utilize putative melanoma neoantigens identified from whole exome sequencing, RNA sequencing, and neoantigen prediction data derived from thirty-six stage III/IV patient tumors. If successful, this effort will expedite clinical translation of neoantigen-specific T cell ACT by validating a robust method for identifying neoantigen-specific TCRs that expands the TCR pool for use in ACT-based immunotherapy applied across indication.