Background Resistance to immune checkpoint inhibitors (ICIs) is common even in tumors with T cell inflammation.1 2 To this end, we interrogated sequelae of ICI-induced T cell inflammation. The current paradigm predicts that ICIs drive T cells to enhance immunity against cancer.2 3 However, little is known regarding consequences of such therapy-induced T cell inflammation within tumor microenvironments (TME) powered by tumor-promoting inflammation which can support myeloid-derived suppressor cells (MDSCs).4 Here, we investigated mechanisms by which ICI-activated T cells can drive inflammatory tumor cells via IL-1 and TNFa to increase G-CSF and CXCL1 production, leading to granulocytic MDSC (G-MDSC) accumulation and, unexpectedly, ICI resistance.
Methods We interrogated mouse and human tumor microenvironments of ICI-responsive and -resistant tumors in the context T cell inflammation. Mouse syngeneic ICI-responsive or ICI-resistant tumor cell lines were implanted into mice to determine the cellular and cytokine composition of the TME following combination anti-PD-1 and -CTLA4 treatment. Mechanisms responsible for T cell-driven ICI resistance were also evaluated in human cancer.
Results The TME immune landscapes of ICI-resistant mouse tumors were characterized by treatment-induced increases in T cell and G-MDSC infiltration, while ICI-responsive tumors were infiltrated by T cells but lacked G-MDSCs. We found that ICI-resistant tumor cells produce G-CSF and CXCL1 in response to IL-1 and TNFa-driven NF-kB signaling to support G-MDSCs. ICI-resistant tumor cells were characterized by higher IL1R1 expression compared to ICI-responsive tumor cells. Inhibition of this resistance axis via neutralization or deletion of IL-1R, TNFa, G-CSF, or G-CSFR improved ICI responsiveness of resistant tumors. We hypothesized that T cell-derived TNFa can drive this resistance axis. In vitro, activated CD8 T cells were sufficient to increase G-CSF and CXCL1 expression from tumor cells in a partially TNFa-dependent manner. In vivo, depletion of T cells abrogated G-CSF and CXCL1 in the TME, and importantly, T cell-specific Tnf deletion improved ICI response. We found that human tumors also engaged this resistance axis in response to IL-1a and TNFa. We interrogated human cancer datasets to demonstrate that TNF-expressing T cells positively correlate with tumor NF-kB transcriptional activity, and showed that signatures of this resistance axis is associated with worse clinical outcome in ICI-treated patients.
Conclusions We report a surprising and novel mechanism of ICI resistance whereby treatment-induced T cell infiltration can paradoxically exacerbate a treatment resistance axis in tumors responsive to IL-1 and TNFa. Our findings refine current models of ICI response and resistance, carrying important therapeutic implications.
Acknowledgements We thank the UCSF Flow Cytometry Core and S. Tamaki for CyTOF maintenance. We thank E. Engleman and J. Bluestone for cell lines. We thank A. Marson and T. Roth for CRISPR-Cas9 reagents, protocols and equipment. We thank the UCSF Clinical Cancer Genomics Laboratory, Molecular Oncology Initiative, and D. Raleigh for access to the UCSF cBioPortal dataset. This study makes use of publicly available data generated by the Lambrechts group in the BioKey study. A full list of investigators who contributed to the generation of the data, and the funding source is available at doi: 10.1038/s41591-021-01323-8/. The Lambrechts group is not responsible for the analysis or interpretation of the data presented. This study was supported by NIH grants DP5 OD023056 and R01 DE032033 to M.H.S., the UCSF Prostate Cancer Program Pilot Award to N.W.C., and NIH S10 OD018040 to procure the CyTOF mass cytometer. N.W.C. is supported by NIH grant T32 5T32AI007334-33. K.J.H-G is supported by the Stanford Propel Postdoctoral Scholarship. R.D. is supported by NIH grant F31 CA265128. J.L.Y. is supported by an NSF GRFP fellowship. M.H.S. is an Investigator of the Parker Institute for Cancer Immunotherapy and of the Chan Zuckerberg Biohub.
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Ethics Approval All mouse work was performed under the UCSF IACUC protocol AN184195–02M. Human dataset analyses were performed under UCSF protocol number 18–24633.
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