Dendritic cells (DC) prime T-cell responses to cancer. CD8+ T-cell priming against tumor antigens is due to cross-presentation of tumor-derived antigens on type 1 conventional DC (DC1) major histocompatibility complex (MHC) molecules. Duong and colleagues revealed a new DC differentiated state that allows type 2-like DCs (DC2) to pick up intact MHC antigen from tumor cells (called “dressing”) and prime CD8+ T-cell responses. A robust interferon-stimulated gene signature (ISG) distinguishes these ISG+ DCs from DC2s. Importantly, when ISG+ DCs were present, antigen presentation and activation of CD8+ T cells occurred in the absence of DC1s. Type I IFN produced by tumors induced the ISG+ DC phenotype. Therapeutic delivery of IFNβ to tumors could generate ISG+ DCs that promoted CD8+ T-cell responses in the absence of DC1s.Expert Commentary: A new class of ISG+ DCs directly picks up and presents tumor cell MHC antigen complexes to prime CD8+ T-cell responses against tumors.Duong E, Fessenden TB, Lutz E, Dinter T, Yim L, Blatt S, et al. Type I interferon activates MHC class I-dressed CD11b+ conventional dendritic cells to promote protective anti-tumor CD8+ T cell immunity. Immunity; Published online November 15, 2021; doi: 10.1016/j.immuni.2021.10.020.Heterogeneity within tumors allows for the development of resistance to therapy and presents a major obstacle to the effective treatment of cancer. Fennell and colleagues developed SPLINTR (single-cell profiling and lineage tracing) to monitor clonal fitness in single cells from genetically driven (MLL-AF9) leukemias in mice. Despite genetic homogeneity, dominant subclones arose across multiple mice. Mixing MLL-AF9 lines with lines carrying either activating mutations in Kras or Flt3 increased the fitness of these lines. However, new subclones were selected within the MLL-AF9 + KrasG12D lines in this competitive setting, versus an isogenic setting. Aggressive chemotherapy similarly selected distinct subclones. Defining features of dominant clones included increased expression of Slpi and decreased expression of genes associated with antigen processing and presentation. Interestingly Slpi, a secreted serine protease inhibitor, only impacted clonal dominance in vivo. Decreased antigen presentation was selected for even when cells developed in immunocompromised (NSG) mice. Importantly, dominant clones retained a tremendous level of transcriptional diversity, potentially increasing their adaptability to varying selective pressures encountered during progression.Expert Commentary: Transcriptional heterogeneity, despite genetic homogeneity, promotes cancer cell fitness, progression, and therapeutic resistance.Fennell KA, Vassiliadis D, Lam EYN, Martelotto LG, Balic JJ, Hollizeck S, et al. Non-genetic determinants of malignant clonal fitness at single-cell resolution. Nature 2022;601:125–31.Triple-negative breast cancers (TNBC), which lack expression of the estrogen receptor (ER), progesterone receptor, and HER2, are highly aggressive and metastatic, displaying shorter survival times in comparison with other subtypes. Liao and colleagues performed comprehensive metabolic profiling and gene expression analysis of breast cancers by comparing TNBC and ER+ patient tumors, patient-derived xenografts (PDX), and cell lines in vivo. They identified “Lipid/Fatty Acid-Enriched” and “Nucleotide/Carbohydrate-Enriched” groups. Pyrimidine metabolism and glutaminolysis pathways were elevated in TNBC. Targeting nucleotide/carbohydrate-enriched TNBC cell lines or PDXs with a pyrimidine biosynthesis inhibitor and/or a glutaminase inhibitor significantly prolonged survival. Interestingly, pyrimidine metabolism inhibition promoted comparable or improved antitumor activity compared with a standard chemotherapy in multiple in vivo models of TNBC.Expert Commentary: A multiomics strategy identified dysregulated metabolic pathways that could be targeted pharmacologically to control rapidly proliferating breast tumor subtypes.Liao C, Glodowski CR, Fan C, Liu J, Mott KR, Kaushik A, et al. Integrated metabolic profiling and transcriptional analysis reveals therapeutic modalities for targeting rapidly proliferating breast cancers. Cancer Research; Published OnlineFirst December 15, 2021; doi: 10.1158/0008-5472.CAN-21-2745.Despite the success of single-gene synthetic lethality screens, targeted therapies have not been identified for most oncogenic-driven cancers. Ito and colleagues speculated that functional redundancy of paralogs may prevent identification of key synthetic lethal interactions with single-gene screens. Therefore, they developed a digenic combinatorial perturbation technology, which allowed for simultaneous paralog pair knockout. They demonstrated that dual DUSP4 and DUSP6 knockout led to growth inhibition of NRAS and BRAF mutant melanoma through ERK hyperactivation, as these genes encode for phosphatases that are essential for regulating MAPK signaling. Furthermore, BRAF mutant melanoma cells resistant to MEK inhibitors were exquisitely sensitive to dual DUSP4/6 loss.Expert Commentary: This proof-of-principle study demonstrated that digenic combinatorial synthetic lethal screens have the potential to identify targetable codependencies in oncogene- driven cancers.Ito T, Young MJ, Li R, Jain S, Wernitznig A, Krill-Burger JM, et al. Paralog knockout profiling identifies DUSP4 and DUSP6 as a digenic dependence in MAPK pathway-driven cancers. Nat Genet 2021;53:1664–72.Sporadic, young-onset colorectal cancer continues to increase worldwide. Patients typically present with advanced disease, with a poor prognosis. Differential multiomic comparisons between young-onset colorectal cancer and old-onset colorectal cancer tissue have not yet yielded useful biomarkers for identifying individuals at higher risk of developing cancer. As it is now well accepted that the gut microbiome changes with age, Yang and colleagues hypothesized that alterations in the gut microbiome could be used as an early biomarker of young-onset colorectal cancer. They found that while overall microbial diversity decreased in both colorectal cancer cohorts relative to age-matched normal control samples, this diversity was significantly higher in young-onset colorectal cancer samples. Flavonifractor plautii, an abundant bacterial species in young-onset colorectal cancer, was a minor constituent of control samples. These microbial alterations resulted in significant changes in metabolism, particularly in DNA-binding and RNA-dependent DNA biosynthetic processes associated with increased cell proliferation and metastases.Expert Commentary: This study suggests a gut microbiome signature as a noninvasive method of early detection for young-onset colorectal cancer.Yang Y, Du L, Shi D, Kong D, Liu J, Liu G, et al. Dysbiosis of human gut microbiome in young onset colorectal cancer. Nat Commun 2021;12:6757. doi: 10.1038/s41467-021-27112-y.The metabolic syndrome is associated with metastatic breast cancer, however, the cellular and molecular pathways that drive breast cancer in type 2 diabetes (T2D) patients are poorly understood. Jafari and colleagues identified a previously unrecognized exosome-mediated cross-talk between T2D adipocytes and breast cancer cells, whereby T2D patient-derived exosomes induced gene expression associated with the epithelial-to-mesenchymal transition (EMT) in breast cancers cells. Exosomal thrombospondin 5 (TSP5) and tumoral bromodomain and extra-terminal (BET) domain protein expression were sufficient and required for EMT to occur. High coexpression of BET domain proteins and TSP5 was associated with a poor prognosis in breast cancer patients.Expert Commentary: This study identified a novel mechanism through which adipocytes in T2D patients contribute to breast cancer tumorigenesis.Jafari N, Kolla M, Meshulam T, Shafran JS, Qiu Y, Casey AN, et al. Adipocyte-derived exosomes may promote breast cancer progression in type 2 diabetes. Sci Signal 2021;14:eabj2807. doi: 10.1126/scisignal.abj2807.Note: Breaking Insights are written by Cancer Research editors. Readers are encouraged to consult the articles referred to in each item for full details on the findings described.