Macrophages target PVR/CD155 on colorectal cancer cells via REVERBalpha

Background&AimsPatients with microsatellite-instable (MSI) colorectal cancer (CRC) benefit from immune checkpoint therapy. For patients with microsatellite-stable (MSS) non-MSI tumors targeting alternative immune checkpoints, such as the Poliovirus receptor (PVR/CD155), may extend response to checkpoint inhibitors and thereby improve outcomes. The drugable transcription factor REVERB (NR1D1) is a master repressor of macrophage function. We hypothesized that regulation of PVR allows elimination of tumor cells by macrophage-directed precision therapy. MethodsHuman CRC cell lines (MSS+: HT29, SW480; MSI+: HCT116), patient-derived organoids (MSS+ PDOs) and tissues were assessed by PCR, Western blot, immunohistochemistry and flow cytometry. 3D co-cultures of CRC cells with macrophages derived from THP1 monocytic leukemia cells or peripheral blood of healthy donors were analysed by microscopy and viability assays. Functional perturbation of PVR and REVERB was achieved by CRISPR/Cas9-sgRNA gene modification, synthetic ligands or blocking antibodies (Abs). ResultsREVERB bound a cognate DNA-element in the -1 kb human PVR gene promoter, and its agonist (SR9009) super-repressed, whereas its antagonist (SR8278) de-repressed transcription of PVR mRNA in macrophages. Macrophages with CRISPR-modified REVERB were unresponsive to ligand, devoid of PVR protein, showed more phagocytosis, tumor cell efferocytosis and expression of genes related to host immunity (PDL1, TLR4 e.a.) than clones with the wild-type receptor. Macrophages lowered the viability of tumor cells, potentiated by PVR blocking Ab or PVR knock-out in tumor cells. Consistently, REVERB antagonist augmented tumor cell death in co-cultures with macrophages and PVR blocking Ab. ConclusionCo-addressing the checkpoint axis REVERB-PVR may represent a novel intervention strategy for patients with MSS+ CRC.