T cells use TNF and IFNγ for paracrine killing with target discrimination programmed by pathogen-derived factors
Cytotoxic T lymphocytes (CTLs) are known to eliminate target cells through perforin-mediated, contact-dependent killing - a process limited by the number of effector T cells despite its serial nature. CTLs likely also possess a mass killing mechanism that can eliminate target cells more efficiently. Using CAR-T cells against B7H3 present on B16 tumor targets, we demonstrate that activated T cells can also kill targets in a perforin-independent manner by releasing diffusible TNF and IFN{gamma} capable of killing nearby targets in a paracrine fashion even if they bear no antigen. Against an unperturbed target, paracrine killing is inefficient but is enhanced by the deletion of TNFR1 signaling molecules such as TAK1, HOIP, or TBK1/IKK{varepsilon}. Notably, these molecules are inhibited naturally by pathogen-encoded antagonists. Expression of a microbial-encoded antagonist, such as the Yersinia-encoded YopJ that antagonizes TAK1 or Ebola-encoded VP35 that antagonizes TBK1/IKK{varepsilon}, alters the target cell response to these cytokines from non-lethal to lethal. We propose that target cells are inherently resistant to killing by TNF and IFN{gamma}, but the presence of a microbial factor alters this sensitivity, providing for the selective elimination of the infected cell while minimizing harm to uninfected bystander cells. We propose the term pathogen-restriction to describe this discriminatory mechanism. Potentially, any microbial-derived factor that crosstalks with the TNF and IFN{gamma} signaling pathways can function as a pathogen-restriction element. GRAPHICAL ABSTRACT O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=129 SRC="FIGDIR/small/696308v1_ufig1.gif" ALT="Figure 1"> View larger version (33K): org.highwire.dtl.DTLVardef@ea6418org.highwire.dtl.DTLVardef@517489org.highwire.dtl.DTLVardef@1ba0e22org.highwire.dtl.DTLVardef@1f5fef8_HPS_FORMAT_FIGEXP M_FIG C_FIG Short SummaryT cells use TNF and IFN{gamma} to kill target cells in a paracrine manner where target elimination is restricted by the presence of pathogen-derived factors.