Using a genome-wide CRISPR KO screen of T cell-mediated killing, Young et al. identified key tumor cell pathways required for (TNFɑ and antigen presentation) and protective against (NF-κB signaling and autophagy) killing. TNFɑ-mediated tumor cell killing was dependent on TNF receptor 1 and caspase activation. Genetic or pharmacologic inactivation of autophagy sensitized tumor cells to TNFɑ/T cell-mediated killing, while inhibition of mTOR signaling increased autophagic activity and decreased sensitivity. The protective role of autophagy was observed in multiple lines, and genetic inactivation of autophagy enhanced the efficacy of anti-PD-1/CTLA-4 therapy.
Contributed by Shishir Pant
ABSTRACT: Although T cell checkpoint inhibitors have transformed the treatment of cancer, the molecular determinants of tumor cell sensitivity to T cell–mediated killing need further elucidation. Here, we describe a mouse genome–scale CRISPR knockout screen that identifies tumor cell TNFα signaling as an important component of T cell–induced apopto- sis, with NF-κB signaling and autophagy as major protective mechanisms. Knockout of individual autophagy genes sensitized tumor cells to killing by T cells that were activated via specific TCR or by a CD3 bispecific antibody. Conversely, inhibition of mTOR signaling, which results in increased autophagic activity, protected tumor cells from T cell killing. Autophagy functions at a relatively early step in the TNFα signaling pathway, limiting FADD- dependent caspase-8 activation. Genetic inactivation of tumor cell autophagy enhanced the efficacy of immune checkpoint blockade in mouse tumor models. Thus, targeting the protective autophagy pathway might sensitize tumors to T cell–engaging immunotherapies in the clinic.