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The airways of the lung are the primary sites of disease in asthma and cystic fibrosis. Here we study the cellular composition and hierarchy of the mouse tracheal epithelium by single-cell RNA-sequencing (scRNA-seq) and in vivo lineage tracing. We identify a rare cell type, the Foxi1 + pulmonary ionocyte; functional variations in club cells based on their location; a distinct cell type in high turnover squamous epithelial structures that we term ‘hillocks’; and disease-relevant subsets of tuft and goblet cells. We developed ‘pulse-seq’, combining scRNA-seq and lineage tracing, to show that tuft, neuroendocrine and ionocyte cells are continually and directly replenished by basal progenitor cells. Ionocytes are the major source of transcripts of the cystic fibrosis transmembrane conductance regulator in both mouse ( Cftr ) and human ( CFTR ). Knockout of Foxi1 in mouse ionocytes causes loss of Cftr expression and disrupts airway fluid and mucus physiology, phenotypes that are characteristic of cystic fibrosis. By associating cell-type-specific expression programs with key disease genes, we establish a new cellular narrative for airways disease. Single-cell RNA sequencing analysis identifies cell types and lineages in airway epithelium, including the pulmonary ionocyte, a new cell type predominantly expressing the cystic fibrosis gene CFTR .

Neuroendocrine tumors (NETs) occur primarily in the small intestine, lung, and pancreas. Due to their rarity compared to other malignancies in these organs, their complex biology remains poorly understood, including their oncogenesis, tumor composition, and the intriguing phenomena of mixed neuroendocrine non-neuroendocrine neoplasms (MiNEN). Here, we profiled ten low-grade small intestine NET (SiNET) samples as well as one mixed lung tumor by single-cell or single-nuclei RNA-seq. We find that SiNETs are largely separated into two distinct subtypes, in which the neuroendocrine cells upregulate epithelial or neuronal markers, respectively. Surprisingly, in both subtypes, the neuroendocrine cells are largely non-proliferative while higher proliferation is observed in multiple non-malignant cell types. Specifically, B and plasma cells are highly proliferative in the epithelial-like SiNET subtype, potentially reflecting the outcome of high Migration Inhibitory Factor (MIF) expression in those tumors, which may constitute a relevant target. Finally, our analysis of a mixed lung neuroendocrine tumor identifies a population of putative progenitor cells that may give rise to both neuroendocrine and non-neuroendocrine (squamous) cells, potentially explaining the origin of the mixed histology. Taken together, our results provide important insights and hypotheses regarding the biology of neuroendocrine neoplasms.

The lungs are a major organ of cancer metastasis. Despite advances in the usage of tumor- specific cytotoxic T cells (CTLs) with potent killing activity (i.e., tumor infiltrating T cells, TILs) for killing of primary tumors, how these T cells encounter and kill metastatic lesions at remote organs is still poorly understood. In the present study we compared the ability of potent neoantigen specific CTLs to kill two types of cancer cells that share the same neoantigen and generate distinct metastatic lesions in the lungs of immunocompetent recipient mice. We have used ovalbumin (OVA) as a neoantigen model and found that the OVA-specific OT-I transgenic CD8 CTLs, when intravenously introduced, readily eliminated primary tumors of OVA-expressing breast cancer E0771 cells. Nevertheless, similar OT-I CTLs failed to clear OVA-expressing breast cancer E0771 cells that colonized the lungs. In contrast, similar intravenously introduced OT-I CTLs efficiently eliminated lung metastatic OVA-expressing B16 melanoma cells, ruling out that the intravenous CTLs were exhausted upon entering the lungs. Three-dimensional (3D) imaging of whole lungs revealed that in both experimental and spontaneous metastasis models, the OVA E0771 cells survived inside lung blood vessels but did not recruit circulating OT-I CTLs to their vicinity. Furthermore, canonical vascular adhesion molecules recognized by the CTLs like ICAM-1 and VCAM-1 were not upregulated nearby the lung-residing intravascular E0771 cells as a potential means to recruit lung circulating CTLs to the vicinity of the intravascular tumor cells. Strikingly, the lung residing OVA-expressing E0771 cells lost expression of their OT-I specific OVA-derived SIINFEKL-H-2Kb pMHC complexes while retaining MHC-I expression. This loss was accompanied by a lung-specific transcriptional reduction of key regulators of MHC-I presentation. A temporal loading of OVA-derived SIINFEKL-H-2Kb pMHC complexes on E0771 cells did not result, however, in cancer cell killing inside the lungs. Nevertheless, direct and stable SIINFEKL peptide presentation on these cells overcame their lung specific escape from OT-I mediated killing. Our study is a first indication that subsets of cancer cells that reside in the lungs rapidly downregulate the expression of neoantigen derived peptide MHC-I complexes and thereby evade killing by intravenously introduced tumor antigen-specific CTLs.

Virally encoded microRNAs (miRNAs) have recently been discovered in herpesviruses. However, their biological roles are mostly unknown. We developed an algorithm for the prediction of miRNA targets and applied it to human cytomegalovirus miRNAs, resulting in the identification of the major histocompatibility complex class I-related chain B (MICB) gene as a top candidate target of hcmv-miR-UL112. MICB is a stress-induced ligand of the natural killer (NK) cell activating receptor NKG2D and is critical for the NK cell killing of virus-infected cells and tumor cells. We show that hcmv-miR-UL112 specifically down-regulates MICB expression during viral infection, leading to decreased binding of NKG2D and reduced killing by NK cells. Our results reveal a miRNA-based immunoevasion mechanism that appears to be exploited by human cytomegalovirus.

The enteric nervous system (ENS) senses microbiota-derived signals and orchestrates mucosal immunity and epithelial barrier functions. However, mechanistic dissections of intestinal neuro-immune-microbiota communications remain challenging. Here, we present an optogenetics-integrated gut organ culture system that enables real-time, whole-tissue stimulation of defined ENS lineages, and detailed analysis of their functional impact. We demonstrate that optogenetic activation of enteric cholinergic neurons rapidly modulates intestinal physiology. Interestingly, distinct neuronal firing patterns differentially modulate neuro-immunological gene expression and epithelial barrier integrity. Furthermore, diverse enteric neuronal lineages exert distinct regulatory roles. While cholinergic activation enhances gene-sets associated with type-2 immunity, tachykininergic neurons modulate distinct mucosal defense programs. Intriguingly, luminal introduction of the immunomodulatory bacterium Thomasclavelia ramosa remodeled cholinergic-induced neuro-immunological transcription. These findings suggest that microbial and neuronal signals are locally integrated to fine-tune gut immunity and barrier defense. Collectively, we provide a powerful platform for systematic discovery and mechanistic exploration of functional neuroimmune connections, and their potential modulation by microbes, drugs or metabolites. The enteric nervous system integrates microbial cues to regulate gut function. Using an optogenetic gut culture model, authors show lineage- and frequency-specific neuronal control of immune responses and barrier integrity, shaped by gut microbes.

Single-cell-based methods such as flow cytometry or single-cell mRNA sequencing (scRNA-seq) allow deep molecular and cellular profiling of immunological processes. Despite their high throughput, however, these measurements represent only a snapshot in time. Here, we explore how longitudinal single-cell-based datasets can be used for deterministic ordinary differential equation (ODE)-based modelling to mechanistically describe immune dynamics. We derived longitudinal changes in cell numbers of colonic cell types during inflammatory bowel disease (IBD) from flow cytometry and scRNA-seq data of murine colitis using ODE-based models. Our mathematical model generalised well across different protocols and experimental techniques, and we hypothesised that the estimated model parameters reflect biological processes. We validated this prediction of cellular turnover rates with KI-67 staining and with gene expression information from the scRNA-seq data not used for model fitting. Finally, we tested the translational relevance of the mathematical model by deconvolution of longitudinal bulk mRNA-sequencing data from a cohort of human IBD patients treated with olamkicept. We found that neutrophil depletion may contribute to IBD patients entering remission. The predictive power of IBD deterministic modelling highlights its potential to advance our understanding of immune dynamics in health and disease.

TOP mRNAs encode components of the translational apparatus, and repression of their translation comprises one mechanism, by which cells encountering amino acid deprivation downregulate the biosynthesis of the protein synthesis machinery. This mode of regulation involves TSC as knockout of TSC1 or TSC2 rescued TOP mRNAs translation in amino acid-starved cells. The involvement of mTOR in translational control of TOP mRNAs is demonstrated by the ability of constitutively active mTOR to relieve the translational repression of TOP mRNA upon amino acid deprivation. Consistently, knockdown of this kinase as well as its inhibition by pharmacological means blocked amino acid-induced translational activation of these mRNAs. The signaling of amino acids to TOP mRNAs involves RagB, as overexpression of active RagB derepressed the translation of these mRNAs in amino acid-starved cells. Nonetheless, knockdown of raptor or rictor failed to suppress translational activation of TOP mRNAs by amino acids, suggesting that mTORC1 or mTORC2 plays a minor, if any, role in this mode of regulation. Finally, miR10a has previously been suggested to positively regulate the translation of TOP mRNAs. However, we show here that titration of this microRNA failed to downregulate the basal translation efficiency of TOP mRNAs. Moreover, Drosha knockdown or Dicer knockout, which carries out the first and second processing steps in microRNAs biosynthesis, respectively, failed to block the translational activation of TOP mRNAs by amino acid or serum stimulation. Evidently, these results are questioning the positive role of microRNAs in this mode of regulation.

Intestinal epithelial cells absorb nutrients, respond to microbes, function as a barrier and help to coordinate immune responses. Here we report profiling of 53,193 individual epithelial cells from the small intestine and organoids of mice, which enabled the identification and characterization of previously unknown subtypes of intestinal epithelial cell and their gene signatures. We found unexpected diversity in hormone-secreting enteroendocrine cells and constructed the taxonomy of newly identified subtypes, and distinguished between two subtypes of tuft cell, one of which expresses the epithelial cytokine Tslp and the pan-immune marker CD45, which was not previously associated with non-haematopoietic cells. We also characterized the ways in which cell-intrinsic states and the proportions of different cell types respond to bacterial and helminth infections: Salmonella infection caused an increase in the abundance of Paneth cells and enterocytes, and broad activation of an antimicrobial program; Heligmosomoides polygyrus caused an increase in the abundance of goblet and tuft cells. Our survey highlights previously unidentified markers and programs, associates sensory molecules with cell types, and uncovers principles of gut homeostasis and response to pathogens. Profiling of 53,193 individual epithelial cells from the mouse small intestine identifies previously unknown cell subtypes and corresponding gene markers, providing insight into gut homeostasis and response to pathogens. Surveying the stomach wall Intestinal epithelial cells can sense and respond to microbial stimuli to support their barrier function and coordinate appropriate immune responses, which range from tolerance to active immunity in cases of pathogen infection. In this study, Aviv Regev, Ramnik Xavier and colleagues used single-cell expression profiling to provide a comprehensive analysis of the epithelial cell composition of mouse small intestines when healthy and after infection, providing new markers, transcriptional programs and organizational principles of gut homeostasis and physiology.

Androgen deprivation is the cornerstone of prostate cancer treatment. It results in involution of the normal gland to ~90% of its original size because of the loss of luminal cells. The prostate regenerates when androgen is restored, a process postulated to involve stem cells. Using single-cell RNA sequencing, we identified a rare luminal population in the mouse prostate that expresses stemlike genes (Sca1⁺ and Psca⁺) and a large population of differentiated cells (Nkx3.1⁺, Pbsn⁺). In organoids and in mice, both populations contribute equally to prostate regeneration, partly through androgen-driven expression of growth factors (Nrg2, Rspo3) by mesenchymal cells acting in a paracrine fashion on luminal cells. Analysis of human prostate tissue revealed similar differentiated and stemlike luminal subpopulations that likewise acquire enhanced regenerative potential after androgen ablation. We propose that prostate regeneration is driven by nearly all persisting luminal cells, not just by rare stem cells.

Nasal vaccination elicits a humoral immune response that provides protection from airborne pathogens 1 , yet the origins and specific immune niches of antigen-specific IgA-secreting cells in the upper airways are unclear 2 . Here we define nasal glandular acinar structures and the turbinates as immunological niches that recruit IgA-secreting plasma cells from the nasal-associated lymphoid tissues (NALTs) 3 . Using intact organ imaging, we demonstrate that nasal vaccination induces B cell expansion in the subepithelial dome of the NALT, followed by invasion into commensal-bacteria-driven chronic germinal centres in a T cell-dependent manner. Initiation of the germinal centre response in the NALT requires pre-expansion of antigen-specific T cells, which interact with cognate B cells in interfollicular regions. NALT ablation and blockade of PSGL-1, which mediates interactions with endothelial cell selectins, demonstrated that NALT-derived IgA-expressing B cells home to the turbinate region through the circulation, where they are positioned primarily around glandular acinar structures. CCL28 expression was increased in the turbinates in response to vaccination and promoted homing of IgA + B cells to this site. Thus, in response to nasal vaccination, the glandular acini and turbinates provide immunological niches that host NALT-derived IgA-secreting cells. These cellular events could be manipulated in vaccine design or in the treatment of upper airway allergic responses. Nasal vaccination induces B cell expansion in the nasal-associated lymphoid tissues, followed by homing to the nasal turbinates and glandular acinar structures.