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Summary Large-scale genomic characterization of tumors from prospective cohort studies may yield new insights into cancer pathogenesis. We performed whole-exome sequencing of 619 incident colorectal cancers (CRCs) and integrated the results with tumor immunity, pathology, and survival data. We identified recurrently mutated genes in CRC, such as BCL9L, RBM10, CTCF, and KLF5, that were not previously appreciated in this disease. Furthermore, we investigated the genomic correlates of immune-cell infiltration and found that higher neoantigen load was positively associated with overall lymphocytic infiltration, tumor-infiltrating lymphocytes (TILs), memory T cells, and CRC-specific survival. The association with TILs was evident even within microsatellite-stable tumors. We also found positive selection of mutations in HLA genes and other components of the antigen-processing machinery in TIL-rich tumors. These results may inform immunotherapeutic approaches in CRC. More generally, this study demonstrates a framework for future integrative molecular epidemiology research in colorectal and other malignancies.

In adult skin, epithelial hair follicle stem cells (SCs) reside in a quiescent niche and are essential for cyclic bouts of hair growth. Niche architecture becomes pronounced postnatally at the start of the first hair cycle. Whether SCs exist or function earlier is unknown. Here we show that slow-cycling cells appear early in skin development, express SC markers, and later give rise to the adult SC population. To test whether these early slow-cycling cells function as SCs, we use Sox9-Cre for genetic marking and K14-Cre to embryonically ablate Sox9, an essential adult SC gene. We find that the progeny of Sox9-expressing cells contribute to all skin epithelial lineages and Sox9 is required for SC specification. In the absence of early SCs, hair follicle and sebaceous gland morphogenesis is blocked, and epidermal wound repair is compromised. These findings establish the existence of early hair follicle SCs and reveal their physiological importance in tissue morphogenesis. [ABSTRACT FROM AUTHOR]

Checkpoint blockade with antibodies specific for the PD-1 and CTLA-4 inhibitory receptors can induce durable responses in a wide range of human cancers. However, the immunological mechanisms responsible for severe inflammatory side effects remain poorly understood. Here we report a comprehensive single-cell analysis of immune cell populations in colitis, a common and severe side effect of checkpoint blockade. We observed a striking accumulation of CD8 T cells with highly cytotoxic and proliferative states and no evidence of regulatory T cell depletion. T cell receptor (TCR) sequence analysis demonstrated that a substantial fraction of colitis-associated CD8 T cells originated from tissue-resident populations, explaining the frequently early onset of colitis symptoms following treatment initiation. Our analysis also identified cytokines, chemokines, and surface receptors that could serve as therapeutic targets for colitis and potentially other inflammatory side effects of checkpoint blockade. • Mechanisms of inflammatory adverse events induced by checkpoint blockade • Colitis-associated differentiation of CD8 Trm cells to cytotoxic effector cells • Persistence and expansion of CTLA-4+ Treg cells • Inflammatory pathways provide opportunities for therapeutic intervention Single-cell analyses of immune checkpoint blockade-associated colitis patient samples reveal enrichment of regulatory T cells in colitic lesions and nominate inflammatory pathways for potential therapeutic intervention. [ABSTRACT FROM AUTHOR]

Obesity is a major modifiable risk factor for pancreatic ductal adenocarcinoma (PDAC), yet how and when obesity contributes to PDAC progression is not well understood. Leveraging an autochthonous mouse model, we demonstrate a causal and reversible role for obesity in early PDAC progression, showing that obesity markedly enhances tumorigenesis, while genetic or dietary induction of weight loss intercepts cancer development. Molecular analyses of human and murine samples define microenvironmental consequences of obesity that foster tumorigenesis rather than new driver gene mutations, including significant pancreatic islet cell adaptation in obesity-associated tumors. Specifically, we identify aberrant beta cell expression of the peptide hormone cholecystokinin (Cck) in response to obesity and show that islet Cck promotes oncogenic Kras -driven pancreatic ductal tumorigenesis. Our studies argue that PDAC progression is driven by local obesity-associated changes in the tumor microenvironment and implicate endocrine-exocrine signaling beyond insulin in PDAC development. • Obesity accelerates oncogenic Kras -driven pancreatic ductal tumorigenesis in mice • Genetic or dietary weight loss intercepts pancreatic cancer progression • Obesity is associated with aberrant pancreatic islet cholecystokinin expression • Islet cholecystokinin overexpression drives pancreatic ductal cancer development Obesity is an intrinsic driver of PDAC in mice, leading to a remodeling of beta cells to increase CCK secretion and playing a role early in pancreatic cancer development that can be intercepted by weight loss. [ABSTRACT FROM AUTHOR]

Summary In lymph nodes (LNs), dendritic cells (DCs) are thought to dispose of apoptotic cells, a function pertaining to macrophages in other tissues. We found that a population of CX3CR1 + MERTK + cells located in the T cell zone of LNs, previously identified as DCs, are efferocytic macrophages. Lineage-tracing experiments and shield chimeras indicated that these T zone macrophages (TZM) are long-lived macrophages seeded in utero and slowly replaced by blood monocytes after birth. Imaging the LNs of mice in which TZM and DCs express different fluorescent proteins revealed that TZM—and not DCs—act as the only professional scavengers, clearing apoptotic cells in the LN T cell zone in a CX3CR1-dependent manner. Furthermore, similar to other macrophages, TZM appear inefficient in priming CD4 T cells. Thus, efferocytosis and T cell activation in the LN are uncoupled processes designated to macrophages and DCs, respectively, with implications to the maintenance of immune homeostasis. [ABSTRACT FROM AUTHOR]

Prognostically relevant RNA expression states exist in pancreatic ductal adenocarcinoma (PDAC), but our understanding of their drivers, stability, and relationship to therapeutic response is limited. To examine these attributes systematically, we profiled metastatic biopsies and matched organoid models at single-cell resolution. In vivo, we identify a new intermediate PDAC transcriptional cell state and uncover distinct site- and state-specific tumor microenvironments (TMEs). Benchmarking models against this reference map, we reveal strong culture-specific biases in cancer cell transcriptional state representation driven by altered TME signals. We restore expression state heterogeneity by adding back in vivo-relevant factors and show plasticity in culture models. Further, we prove that non-genetic modulation of cell state can strongly influence drug responses, uncovering state-specific vulnerabilities. This work provides a broadly applicable framework for aligning cell states across in vivo and ex vivo settings, identifying drivers of transcriptional plasticity and manipulating cell state to target associated vulnerabilities., Competing Interests: Declaration of interests B.M.W. reports research support from Celgene and Eli Lilly and consulting for BioLineRx, Celgene, G1 Therapeutics, and GRAIL. W.C.H. is a consultant for Thermo Fisher, Solasta Ventures, MPM Capital, Tyra Biosciences, iTeos, Frontier Medicines, Function Oncology, KSQ Therapeutics, Jubilant Therapeutics, RAPPTA Therapeutics, and Paraxel. A.K.S. reports compensation for consulting and/or SAB membership from Merck, Honeycomb Biotechnologies, Cellarity, Repertoire Immune Medicines, Ochre Bio, Third Rock Ventures, Hovione, Relation Therapeutics, FL82, and Dahlia Biosciences. A.J.A. has consulted for Oncorus, Arrakis Therapeutics, and Merck & Co. and has research funding from Mirati Therapeutics, Syros, Deerfield, and Novo Ventures that are unrelated to this project. S.R.M. is a founder of Travera. S.R. has equity in Amgen. J.M.C. has received research funding from Merck, Tesaro, AstraZeneca, Bayer, and Esperas Pharma; has served as a consultant to Bristol Myers Squibb; and has received travel funding from Bristol Myers Squibb. A.R. is an employee of AstraZeneca and an equity holder in Celsius Therapeutics and NucleAI. Y.Y.L. reports equity from g.Root Biomedical Services. A.D. Cherniack reports research support from Bayer. R.J.S reports research support from Merck and consulting and/or SAB membership for Bristol Myers Squibb, Merck, Novartis, and Pfizer. G.I.S. reports sponsored research support from Eli Lilly, Merck KGaA/EMD-Serono, Merck, and Sierra Oncology and has served on advisory boards for Pfizer, Eli Lilly, G1 Therapeutics, Roche, Merck KGaA/EMD-Serono, Sierra Oncology, Bicycle Therapeutics, Fusion Pharmaceuticals, Cybrexa Therapeutics, Astex, Almac, Ipsen, Bayer, Angiex, Daiichi Sankyo, Seattle Genetics, Boehringer Ingelheim, ImmunoMet, Asana, Artios, Atrin, Concarlo Holdings, Syros, Zentalis, CytomX Therapeutics, Blueprint Medicines, and Kymera Therapeutics. T.J. is a member of the Board of Directors of Amgen and Thermo Fisher Scientific; a co-Founder of Dragonfly Therapeutics and T2 Biosystems; serves on the Scientific Advisory Board of Dragonfly Therapeutics, SQZ Biotech, and Skyhawk Therapeutics; and is the President of Break Through Cancer. None of these affiliations represent a conflict of interest with respect to the design or execution of this study or interpretation of data presented in this manuscript. T.J.’s laboratory currently also receives funding from the Johnson & Johnson Lung Cancer Initiative and The Lustgarten Foundation for Pancreatic Cancer Research, but this funding did not support the research described in this manuscript. K.N. reports research support from Revolution Medicines, Evergrande Group, Pharmavite, and Janssen; is a member of SABs for SeaGen, BiomX, and Bicara Therapeutics; and has consulted for X-Biotix Therapeutics and Redesign Health. A.K.S., P.S.W., A.W.N., S.R., W.C.H., A.J.A., B.W.M., and J.G.R. have filed a patent (Publication number WO/2021/081491; International application number PCT/US2020/057342) related to this work., (Copyright © 2021 The Author(s). Published by Elsevier Inc. All rights reserved.)