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Background Renal cell carcinoma (RCC) frequently exhibits favorable responses to immunotherapy, despite a low tumor mutational burden, suggesting a critical role for non-mutational antigens presented by human leukocyte antigen class I in activating CD8 + T cells.Methods To systematically identify non-canonical tumor-specific antigens, we developed an integrated proteogenomic approach to RCC samples by combining immunopeptidomics with exome and transcriptome sequencing. We subsequently primed and expanded antigen-reactive T cells in vitro, isolated a panel of antigen-specific T-cell receptors, and characterized their functionality. Finally, we investigated the tumor-killing and regression of non-canonical antigen-reactive T cells using patient-derived tumor-like cell clusters and mouse models.Results We discovered a diverse repertoire of non-canonical tumor-specific antigens derived from human endogenous retroviruses (hERVs) and long non-coding RNAs (lncRNAs), many of which were shared across patients. Single-cell RNA sequencing further revealed that T cells reactive to these antigens were enriched within exhausted subsets in the tumor microenvironment, indicative of persistent antigen-specific stimulation. Functionally, T cells engineered to recognize these non-canonical antigens mediated potent tumor cell killing both in vitro and in vivo. Our findings establish hERV-derived and lncRNA-derived antigens as key drivers of RCC immunogenicity and highlight their strong potential as targets for T-cell-based immunotherapy.Conclusions Our work is the first to demonstrate that non-canonical antigens drive immunogenicity in low-mutation RCC, thereby resolving a key question in cancer immunology—how tumors with low mutational burden can provoke robust T-cell responses.