Abstract
T cell engagers (TCEs) redirect T cells to kill tumors by cross-linking CD3ε to a tumor antigen, independently of T cell receptor specificity. Some patients achieve remissions that persist long after drug clearance, but whether TCEs can couple acute cytotoxicity to the generation of lasting adaptive immunity remains unknown. Here, using an immunocompetent mouse model for clinical-grade human TCEs, we show that TCE-mediated killing initiates an endogenous vaccination cascade. Intravital two-photon imaging reveals a perforin-dependent cytotoxic wave that peaks within 24 hours, then subsides despite massive T cell accumulation. Single-cell transcriptomics and adoptive transfers demonstrate that memory CD8⁺ T cells, the principal effector reservoir in mouse and human, transit through a progenitor-like state before differentiating into cytotoxic effectors with recall competence. Crucially, tumor lysis fuels cross-priming of tumor-specific CD8⁺ T cells by XCR1⁺ type 1 conventional dendritic cells, a cDC1-dependent step essential for durable tumor control and protective memory upon rechallenge.