SUMMARY Serrated adenocarcinoma, an alternative pathway for colorectal cancer (CRC) development, accounts for 15–30% of all CRCs and is aggressive and treatment-resistant. We show that the expression of atypical protein kinase c (PKC)ζ and PKC λ/ι was reduced in human serrated tumors. Simultaneous inactivation of these genes in the mouse intestinal epithelium resulted in spontaneous serrated tumorigenesis that progressed to advanced cancer with a strongly reactive and immunosuppressive stroma. Whereas epithelial PKCλ/ι deficiency led to immunogenic cell death and the infiltration of CD8+ T cells, which repressed tumor initiation, PKCζ loss impaired interferon and CD8+ T cell responses, which resulted in tumorigenesis. Combined treatment with a TGF-β receptor inhibitor plus anti-PDL1 checkpoint blockade showed synergistic curative activity. Analysis of human samples supported the relevance of these kinases in the immunosurveillance defects of human serrated CRC. These findings provide insight into avenues for the detection and treatment of this poor-prognosis subtype of CRC.

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Conventional dendritic cells (cDC) are professional antigen-presenting cells that induce immune activation or tolerance. Two functionally specialised populations, termed cDC1 and cDC2, have been described in humans, mice, ruminants and recently in pigs. Pigs are an important biomedical model species and a key source of animal protein; therefore further understanding of their immune system will help underpin the development of disease prevention strategies. To characterise cDC populations in porcine blood, DC were enriched from PBMC by CD14 depletion and CD172a enrichment then stained with lineage mAbs (Lin; CD3, CD8α, CD14 and CD21) and mAbs specific for CD172a, CD1 and CD4. Two distinct porcine cDC subpopulations were FACSorted CD1− cDC (Lin−CD172+ CD1−CD4−) and CD1+ cDC (Lin−CD172a+ CD1+ CD4−), and characterised by phenotypic and functional analyses. CD1+ cDC were distinct from CD1− cDC, expressing higher levels of CD172a, MHC class II and CD11b. Following TLR stimulation, CD1+ cDC produced IL-8 and IL-10 while CD1− cDC secreted IFN-α, IL-12 and TNF-α. CD1− cDC were superior in stimulating allogeneic T cell responses and in cross-presenting viral antigens to CD8 T cells. Comparison of transcriptional profiles further suggested that the CD1− and CD1+ populations were enriched for the orthologues of cDC1 and cDC2 subsets respectively.