Phosphatidylethanolamine lipids secreted by CD8⁺ T cells mediate cytotoxic immunity

Current understanding of T-cell immunity largely focuses on protein factors responsible for immune surveillance and regulation, with limited exploration of the roles played by other molecular types. While proteins such as perforin and granzymes are well-established mediators of CD8⁺ T cell cytotoxicity 1-5 , our study uncovers the cone-shaped phosphatidylethanolamine (PE) lipids as a new class of effector molecules with broad cytotoxic functions against tumor and infected cells. Upon activation, CD8⁺ T cells upregulated the de novo biosynthesis pathway to produce substantial amounts of PE lipids carrying polyunsaturated or monounsaturated fatty acid sidechains. The newly synthesized PE lipids were packaged into vesicular compartments distinct from Lamp1⁺ granules, rapidly polarized to immunological synapses, and secreted through the membrane fusion protein Munc13-4, generating PE⁺ extracellular vesicles enriched in synaptic lipids and proteins. CD8-derived PE lipids were efficiently taken up by target cells and transported to the endoplasmic reticulum via Esyt1, where excessive PE loading induced ER stress and triggered Chop-dependent cell death within a few hours. The PE pathway functioned independently of conventional cytotoxic mechanisms and remained effective even when those pathways were absent. Manipulation of the PE-Esyt1-ER stress axis markedly altered T cell cytotoxicity, and ethanolamine pretreatment of T cells enhanced the efficacy of adoptive cell therapy. These findings introduce a new lipid-based mechanism of cytotoxic immunity and underscore the importance of non-protein molecules as immune effectors.