A high-throughput RNAi screen for detection of immune-checkpoint molecules that mediate tumor resistance to cytotoxic T lymphocytes.
Bottom Line: Tumor-immune resistance is mediated by cell surface ligands that engage immune-inhibitory receptors on T cells.These ligands represent potent targets for therapeutic inhibition.So far, only few immune-suppressive ligands have been identified.
Affiliation: Division of Translational Immunology, German Cancer Research Center (DKFZ), Heidelberg, Germany email@example.com firstname.lastname@example.org.Show MeSH
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Mentions: We finally explored the influence of CCR9 expression on CTL functions. CCR9 knockdown in MCF7 cells significantly increased the secretion of IFN-γ and granzyme B by survivin-specific CTL in response to MCF7 cells (Fig5A and B), supporting the increased cytotoxicity observed in the kill assays. To assess whether this correlated with increased TCR activation and signaling, we performed TCR phospho-plex analysis in survivin-specific CTLs after contact with CCR9hi or CCR9lo MCF7 cells. With the exception of some degree of reduced Lck phosphorylation (which was detectable only 5 min after exposure to CCR9lo tumor cells), we did not observe any CCR9-dependent changes in TCR signaling (Supplementary Fig S2A and B). Nevertheless, TCR engagement was found to be necessary for CCR9-mediated immunosuppression as polyclonal T cells failed to secrete higher levels of IFN-γ in response to CCR9lo MCF7 cells in the absence of anti-EpCAM x CD3 bi-specific antibody (Supplementary Fig S3). One alternative route of T cell activation is the STAT (signal transducer and activator of transcription) family of transcription factors which regulate cytokine expression in T cells (Yu et al, 2009). CCR9 expressed on MCF7 cells significantly inhibited the secretion of the T-helper-1 (Th1) cytokines including tumor necrosis factor-alpha (TNF-α), interleukin-2 (IL-2), and (to a minor extent) of IFN-γ as well as IL-17, while the secretion of IL-10 was slightly but consistently increased (Fig5C). Accordingly, we observed a significant increase in STAT1 and STAT2 signaling in survivin-specific T cells upon coculture with CCR9lo MCF7 cells, suggesting that anti-tumor type-1 immune response is impeded by tumor-specific CCR9 (Fig5D and E).
Affiliation: Division of Translational Immunology, German Cancer Research Center (DKFZ), Heidelberg, Germany email@example.com firstname.lastname@example.org.