Top Reads

Open reading frame 8 is a secreted protein encoded in the SARS-CoV-2 genome. Previous reports implicated ORF8 as an IL-17R agonist in macrophages and monocytes that contributes to the “cytokine storm” associated with severe COVID. In this Top Read, Ponde et al. (p. 252) showed that ORF8-induced cytokine signaling is not mediated by IL-17R, but by MyD88, in monocytes and macrophages. First, IL-17 treatment of bone marrow–derived macrophages (BMDMs), monocyte/macrophage cell lines, or primary human monocytes isolated from healthy donor PBMCs did not upregulate cytokine transcripts typically ascribed to IL-17 signaling in other cell types, whereas LPS and ORF8 did. Furthermore, Il17rc transcripts were not detectable in SARS-CoV-2–infected human or mouse monocytes or macrophages. Finally, using Myd88^−/− or Il17ra^−/− knockout BMDMs and Abs against IL-17RA or IL-17RC, the authors showed that ORF8 acts independently of IL-17RA and IL-17RC, but requires MyD88. Together, the data confirm that ORF8 induces inflammatory cytokines in monocytes and macrophages, but that its proinflammatory role in COVID is mediated by MyD88 independently of IL-17R signaling.

In this Top Read, Millrine et al. (p. 274) show that effector T cells modify transcription of IL-6 during inflammation through a regulatory interplay between STAT1 and STAT3. Under inflammatory conditions, the presence of Th1 T cells altered gene expression in stromal cells, enhancing transcripts downstream of STAT1, STAT 3, and IFN-γ signaling. In Il6-deficient mice, chromatin remodeling during inflammation facilitated a switch from STAT3 binding to STAT1 binding in the presence of Th1 cells, but not under inflammatory conditions alone. The Th1 cells modified Jak–STAT cytokine signaling by redirecting STAT transcription factors to conserved DNA sequences, which did not bind STAT factors during inflammation in the absence of Th1 cells. Finally, the authors used publicly available genome-wide association studies (GWAS) to show that the GAS-Alu motif is present in numerous studies of immune regulation and immune pathologies. Clustering analysis of these GWAS identified one cluster with an enrichment of IL-6 and IFN-γ gene signatures. Thus, the authors have provided insight into how certain inflammatory conditions and/or disease processes can alter transcription factor access to specific enhancers.

In this Top Read, Miller et al. (p. 295) show that the TLR9 agonist, PIP-CpG, enhances the CD8⁺ T cell response to spontaneous tumors. Treatment of MMTV-PyMT mice, a transgenic model of spontaneous breast cancer, with PIP-CpG, showed a regression of established tumors, delayed new tumor growth, and prolonged survival. The treated mice had increased numbers of CD8⁺ T cells, which were required for optimal antitumor effects. Tumors from mice treated with PIP-CpG had increased expression of chemokines known to recruit various types of immune cells, including T cells, macrophages, NK cells, dendritic cells, and myeloid-derived suppressor cells. Additionally, tumors secreted several cytokines that support CD8⁺ T cell responses, leading to enrichment of activated and proliferating T cells within the tumors. Enhanced Ag presentation function in B cells and more activated mature NK cells within the tumor microenvironment was also seen following PIP-CpG treatment. These data demonstrate that PIP-CpG is an effective immunotherapy that could be an alternative treatment for tumors that are unresponsive to checkpoint inhibitor therapy.

Antisense oligonucleotides (ASOs) have been approved for therapy in several human diseases. In this Top Read, Kaufmann et al. (p. 287) described an ASO that targets the nucleotide-binding and oligomerization domain-like receptor family, pyrin domain containing 3 (NLRP3) inflammasome and shows preclinical efficacy in the treatment of cryopyrin-associated periodic syndrome (CAPS) in mice. An initial screen for potential Nlrp3-specific ASOs yielded a candidate that downregulated Nlrp3 mRNA in several cell lines. In bone marrow–derived macrophages from both wild-type and knock-in mouse models of CAPS, the ASO reduced Il-1β release but did not kill cells. In vivo, treatment of CAPS mice with ASO increased survival, prevented CAPS symptoms, in particular systemic inflammation that manifests as increased spleen weight and neutrophil infiltration in the skin, and downregulated Nlrp3 mRNA as well as IL-1β in peripheral blood, liver, and kidney. This NLRP3-specific ASO, therefore, is a potentially novel treatment for patients suffering from systemic inflammation caused by the rare autoinflammatory disorder CAPS who do not respond to current IL-1–targeted treatments.