Understanding how G-protein coupled receptor (GPCR) expression affects cell positioning within diverse tissue microenvironments is essential for elucidating immune cell trafficking mechanisms. We present a competitive homing assay designed to study GPCR-mediated T-cell localization to organs expressing their cognate chemoattractant ligands, applicable for both short-term and long-term studies. The approach involves an improved protocol for recombinant murine stem cell virus (MSCV) transduction of T cells to express the GPCR of interest or a control construct, followed by competitive homing in recipient mice. Cell distribution across different organs is analyzed using flow cytometry and/or confocal microscopy. In short-term experiments (10-12 h), confocal microscopy revealed distinct cell localization patterns, including to alveoli, bronchi submucosa, venous sites, and interstitium in the lung, as well as the epithelium lining the trachea, stomach, and uterine horn. In long-term studies (1-7 weeks), flow cytometry provided insights into preferential cell accumulation, revealing dynamic changes and potential maturation or repositioning within tissues over time. This competitive homing assay is a robust tool for studying GPCR-mediated cell positioning, offering valuable insights into tissue-specific distribution and potential applications in immunology and therapeutic research.

Hematopoietic cell mobilization is essential for physiologic stress responses and therapeutic applications. Cobalt protoporphyrin IX (CoPP), a structural heme analog, induces granulocyte colony-stimulating factor (G-CSF) and other cytokines. We aimed to uncover mechanisms driving cytokine induction during mobilization and assess whether these factors are transcriptionally coregulated.We treated mice with recombinant human G-CSF (rhG-CSF) and CoPP as mobilizing agents and evaluated gene expression and hematopoietic cell composition in bone marrow (BM) and peripheral blood (PB) from 3 hours to 26 days posttreatment. We supplemented manual gating of flow cytometry data with clustering algorithms to identify cell populations.Both neutrophils and hematopoietic stem and progenitor cells were mobilized more rapidly by rhG-CSF; however, the mobilization was stronger and more sustained in mice treated with CoPP. Neutrophils mobilized by G-CSF were phenotypically less mature, including a population of c-kit–expressing cells, and showed impaired phagocytosis of bacterial particles. scRNAseq and Luminex assay revealed that S100A8 alarmin was increased by CoPP in stromal, endothelial, and hematopoietic cells at the mRNA level and in plasma at the protein level, indicating its potential role as a mediator of mobilization. Bioinformatics tools (Enrichr, SEA from MEME Suite, and STRING) identified Maz, Egr1, and Sp3 as potential transcriptional regulators of CoPP-induced cytokines.The distinct kinetics of CoPP- and rhG-CSF–induced mobilization and regeneration suggest the involvement of additional cytokines that modulate the effects of G-CSF. CoPP-induced cytokines might be coregulated at the transcriptional level, as suggested by enriched transcription factor motifs, potentially indicating a coordinated regulatory mechanism that contributes to hematopoietic mobilization.

Sustained lymphocyte migration from blood into lymph nodes (LNs) is important for immune responses. The CC-chemokine receptor-7 (CCR7) ligand CCL21 is required for LN entry but is downregulated during inflammation, and it has been unclear how recruitment is maintained. Here, we show that the oxysterol biosynthetic enzyme cholesterol-25-hydroxylase (Ch25h) is upregulated in LN high endothelial venules during viral infection. Lymphocytes become dependent on oxysterols, generated through a transcellular endothelial-fibroblast metabolic pathway, and the receptor EBI2 for inflamed LN entry. Additionally, Langerhans cells are an oxysterol source. Ch25h is also expressed in inflamed peripheral endothelium, and EBI2 mediates B cell recruitment in a tumor model. Finally, we demonstrate that LN CCL19 is critical in lymphocyte recruitment during inflammation. Thus, our work explains how naive precursor trafficking is sustained in responding LNs, identifies a role for oxysterols in cell recruitment into inflamed tissues, and establishes a logic for the CCR7 two-ligand system.

T cell scarcity in tumor tissues poses a critical challenge to cancer immunotherapy. Here we manipulate the tumor vasculature, an essential regulator of immune cell trafficking, to reinvigorate anti-tumor T cell responses in "cold" tumors. We show that ectopic pan-endothelial expression of COUP-TFII, a master transcription factor for venous development, induces molecular programs of post-capillary venules in tumor endothelium. Venular reprogramming selectively promotes T cell recruitment into tumors, inhibits tumor growth in mouse models of breast and pancreatic cancers, and sensitizes tumors to immune checkpoint blockade and adoptive T cell transfer therapies. Mechanistic studies show that enhanced recruitment of anti-tumor T cells and tumor inhibition are mediated by COUP-TFII-induced vascular adhesion receptors. Our study supports a pivotal role of vascular endothelial cells in governing tumor immune evasion, and proposes venular reprogramming as a therapeutic strategy to bolster anti-tumor immunity and immunotherapy.

Progenitors of intraepithelial T cells (IELps) migrate from the thymus to the intestines after birth where they develop into unconventional TCRγδ and TCRαβ lymphocytes in a process of extrathymic lymphopoiesis within cryptopatches. Mechanisms of IELp migration have remained unclear. Here we show that thymic IELps express the somatostatin receptor SSTR2, which contributes to their homing to the gut. IELp homing is Sstr2 dependent and correlates with neonatal induction of Sst encoding somatostatin in neuroendocrine and lamina propria stromal cells. The SSTR2 ligands somatostatin and cortistatin attract IELps in chemotaxis assays and somatostatin triggers IELp binding to the mucosal vascular addressin MAdCAM1. T cell transduction with Sstr2 confers homing to the neonatal colon. Human fetal thymic IELp-like cells express SSTR2 and intestinal stromal cells express SST at the time of initial T cell population, suggesting conserved mechanisms of progenitor seeding of the developing intestines. These results reveal an unexpected role for the SSTR2-somatostatin axis in early immune system development and describe a new role for a small peptide hormone G-protein-coupled receptor in developmental lymphocyte trafficking.

High endothelial cells (HECs) and intestinal goblet cells (GCs) are highly specialized through organelle expansion and metabolism for production of sulfated mucins essential for lymphocyte homing and mucosal defense, respectively. How these cells coordinate organelle architecture and biosynthetic pathways to support such demands remains poorly understood. Here, we show at single-cell resolution that HECs rely on gene regulatory networks driven by IRE1α-XBP1 and CREB3L1/2 transcription factors. These networks upregulate enzymes and transporters that control inter-organelle metabolic fluxes for the step-wise assembly of sulfated O-glycan synthesis, while scaling the endoplasmic reticulum (ER) and Golgi apparatus, reinforcing cargo trafficking and organizing sequential glycosyltransferase deployment. Genetic and pharmacological perturbations show that these transcriptional circuits sustain lymph node HEC morphology and function in lymphocyte homing, and drive ectopic induction of HEV during inflammation. Parallel transcriptional networks operate in GCs. Together, our findings define a conserved regulatory logic that integrates metabolic pathways and organelle architecture to enable committed sulfo-mucin cell specialization across distinct tissue contexts.

T cell scarcity in tumor tissues poses a critical challenge to cancer immunotherapy. Here we manipulate the tumor vasculature, an essential regulator of immune cell trafficking, to reinvigorate anti-tumor T cell responses in “cold” tumors. We show that ectopic pan-endothelial expression of COUP-TFII, a master transcription factor for venous development, induces molecular programs of post-capillary venules in tumor endothelium. Venular reprogramming selectively promoted T cell recruitment into tumors, inhibited tumor growth in mouse models of breast and pancreatic cancers, and sensitized tumors to immune checkpoint blockade and adoptive T cell transfer therapies. Mechanistic studies show that enhanced recruitment of anti-tumor T cells and tumor inhibition are mediated by COUP-TFII-induced vascular adhesion receptors. Our study supports a pivotal role of vascular endothelial cells in governing tumor immune evasion, and proposes venular reprogramming as a novel therapeutic strategy to bolster anti-tumor immunity and immunotherapy.

IL-10 + B cells are critical for immune homeostasis and restraining immune responses in infection, cancer, and inflammation; however, the signals that govern IL-10 + B cell differentiation are ill-defined. Here we find that IL-10 + B cells expand in mice lacking secreted IgM ((s)IgM –/– ) up to 10-fold relative to wildtype (WT) among all major B cell and regulatory B cell subsets. The IL-10 + B cell increase is polyclonal and presents within 24 hours of birth. In WT mice, sIgM is produced prenatally and limits the expansion of IL-10 + B cells. Lack of the high affinity receptor for sIgM, FcμR, in B cells translates into an intermediate IL-10 + B cell phenotype relative to WT or sIgM –/– mice. Our study thus shows that sIgM regulates IL-10 programming in B cells in part via B cell-expressed FcμR, thereby revealing a function of sIgM in regulating immune homeostasis.

Tissue-selective chemoattractants direct lymphocytes to epithelial surfaces to establish local immune environments, regulate immune responses to food antigens and commensal organisms, and protect from pathogens. Homeostatic chemoattractants for small intestines, colon and skin are known1,2, but chemotropic mechanisms selective for respiratory tract and other non-intestinal mucosal tissues remain poorly understood. Here we leveraged diverse omics datasets to identify GPR25 as a lymphocyte receptor for CXCL17, a chemoattractant cytokine whose expression by epithelial cells of airways, upper gastrointestinal and squamous mucosae unifies the non-intestinal mucosal tissues and distinguishes them from intestinal mucosae. Single-cell transcriptomic analyses show that GPR25 is induced on innate lymphocytes before emigration to the periphery, and is imprinted in secondary lymphoid tissues on activated B and T cells responding to immune challenge. GPR25 characterizes B and T tissue resident memory cells and regulatory T lymphocytes in non-intestinal mucosal tissues and lungs in humans and mediates lymphocyte homing to barrier epithelia of the airways, oral cavity, stomach, and biliary and genitourinary tracts in mouse models. GPR25 is also expressed by T cells in cerebrospinal fluid and CXCL17 by neurons, suggesting a role in central nervous system (CNS) immune regulation. We reveal widespread imprinting of GPR25 on regulatory T cells, suggesting a mechanistic link to population genetics evidence that GPR25 is protective in autoimmunity3,4. Our results define a GPR25-CXCL17 chemoaffinity axis with the potential to integrate immunity and tolerance at non-intestinal mucosae and the CNS.

Stromal cells within the tumor tissue promote immune evasion as a critical strategy for cancer development and progression, but the underlying mechanisms remain poorly understood. In this study, we explore the role of endothelial cells (ECs) in the regulation of the immunosuppressive tumor microenvironment. Using mouse pancreatic ductal adenocarcinoma (PDAC) models, we found that canonical Notch signaling in endothelial cells suppresses the recruitment of antitumor T cells and promotes tumor progression by inhibiting the pro-inflammatory functions of cancer-associated fibroblasts (CAFs). Abrogation of endothelial Notch signaling modulates EC-derived angiocrine factors to enhance the pro-inflammatory activities of CAFs, which drive CXCL9/10-CXCR3-mediated T cell recruitment to inhibit tumor growth. Additionally, abrogation of endothelial Notch unleashed interferon gamma responses in the tumor microenvironment, upregulated PDL1 expression on tumor cells, and sensitized PDAC to PD1-based immunotherapy. Collectively, these data uncover a pivotal role of endothelial cells in shaping the immunosuppressive microenvironment, and suggest the potential of targeting EC-CAF interaction as a novel therapeutic modality to boost antitumor immunity.

The intestinal lamina propria contains a diverse network of fibroblasts that provide key support functions to cells within their local environment. Despite this, our understanding of the diversity, location and ontogeny of fibroblasts within and along the length of the intestine remains incomplete. Here we show that the small and large intestinal lamina propria contain similar fibroblast subsets that locate in specific anatomical niches. Nevertheless, we find that the transcriptional profile of similar fibroblast subsets differs markedly between the small intestine and colon suggesting region specific functions. We perform in vivo transplantation and lineage-tracing experiments to demonstrate that adult intestinal fibroblast subsets, smooth muscle cells and pericytes derive from Gli1 -expressing precursors present in embryonic day 12.5 intestine. Trajectory analysis of single cell RNA-seq datasets of E12.5 and adult mesenchymal cells suggest that adult smooth muscle cells and fibroblasts derive from distinct embryonic intermediates and that adult fibroblast subsets develop in a linear trajectory from CD81 + fibroblasts. Finally, we provide evidence that colonic subepithelial PDGFRα hi fibroblasts comprise several functionally distinct populations that originate from an Fgfr2 -expressing fibroblast intermediate. Our results provide insights into intestinal stromal cell diversity, location, function, and ontogeny, with implications for intestinal development and homeostasis.

The recruitment of cells with effector functions into the tumor microenvironment holds potential for delaying cancer progression. We show that subsets of human CD28-effector CD8 T cells, CCR7- CD45RO+ effector memory, and CCR7- CD45RO- effector memory RA phenotypes, express the chemerin receptor CMKLR1 and bind chemerin via the receptor. CMKLR1-expressing human CD8 effector memory T cells present gene, protein, and cytotoxic features of NK cells. Active chemerin promotes chemotaxis of CMKLR1-expressing CD8 effector memory cells and triggers activation of the α4β1 integrin. In an experimental prostate tumor mouse model, chemerin expression is downregulated in the tumor microenvironment, which is associated with few tumor-infiltrating CD8+ T cells, while forced overexpression of chemerin by mouse prostate cancer cells leads to an accumulation of intra-tumor CD8+ T cells. Furthermore, α4 integrin blockade abrogated the chemerin-dependent recruitment of CD8+ T effector memory cells into implanted prostate tumors in vivo. The results identify a role for chemerin:CMKLR1 in defining a specialized NK-like CD8 T cell, and suggest the use of chemerin-dependent modalities to target effector CMKLR1-expressing T cells to the tumor microenvironment for immunotherapeutic purposes.

The hematopoietic niche is a supportive microenvironment comprised of distinct cell types, including specialized vascular endothelial cells that directly interact with hematopoietic stem and progenitor cells (HSPCs). The molecular factors that specify niche endothelial cells and orchestrate HSPC homeostasis remain largely unknown. Using multi-dimensional gene expression and chromatin accessibility analyses, we define a conserved gene expression signature and cis -regulatory landscape unique to sinusoidal endothelial cells in the HSPC niche. Using enhancer mutagenesis and transcription factor overexpression, we elucidate a transcriptional code involving members of the Ets, Sox and Nuclear Hormone Receptor families that is sufficient to induce ectopic niche endothelial cells that associate with mesenchymal stromal cells and support the recruitment, maintenance and division of HSPCs in vivo . These studies set forth an approach for generating synthetic HSPC niches, in vitro or in vivo , and for effective therapies to modulate the endogenous niche.

SummaryScarcity of tumor-infiltrating T cells poses significant challenges to cancer treatment, but mechanisms that regulate T cell recruitment into the tumor microenvironment are unclear. Here we ask if the endothelial lining of tumor vasculature suppresses T cell infiltration. Using mouse pancreatic ductal adenocarcinoma models, we found that Notch signaling in endothelial cells (ECs) inhibits the pro-inflammatory functions of cancer-associated fibroblasts (CAFs) and prevents CAFs from secreting CXCL10, a chemokine that recruits anti-tumor T cells via its receptor CXCR3. Abrogation of canonical Notch signaling in ECs reprogrammed the phenotype of CAFs from myofibroblasts into pro-inflammatory fibroblasts, unleashed interferon gamma (IFNγ) responses in the tumor, and stimulated CXCL10/CXCR3-mediated recruitment of T cells to inhibit tumor growth. Collectively, these data uncover an important role of endothelial Notch signaling in shaping the tumor immune microenvironment, and suggest the potential of targeting EC-CAF crosstalk as an approach to enhance anti-tumor immunity in immunologically cold tumors.In briefHow blood vasculature shapes the tumor immune microenvironment is poorly defined. This study demonstrates that tumor endothelial cells reprogram cancer-associated fibroblasts to limit anti-tumor T cell recruitment, and suggests the potential of targeting endothelium-fibroblast crosstalk to overcome T cell scarcity in “cold” tumors and enhance anti-tumor immunity.

SUMMARYImmunoglobulin family and carbohydrate vascular addressins encoded byMadcam1andSt6gal1control lymphocyte homing into intestinal tissues, regulating immunity and inflammation. The addressins are developmentally programmed to decorate endothelial cells lining gut post-capillary and high endothelial venules, providing a prototypical example of organ- and segment-specific endothelial specialization. We identify conserved NKX-COUP-TFII composite elements (NCCE) in regulatory regions ofMadcam1andSt6gal1that bind intestinal homeodomain protein NKX2-3 cooperatively with venous nuclear receptor COUP-TFII to activate transcription. TheMadcam1element also integrates repressive signals from arterial/capillary Notch effectors. Pan-endothelial COUP-TFII overexpression induces ectopic addressin expression in NKX2-3+capillaries, while NKX2-3 deficiency abrogates expression by HEV. Phylogenetically conserved NCCE are enriched in genes involved in neuron migration and morphogenesis of the heart, kidney, pancreas and other organs. Our results define a genomic address code for targeted expression of mucosal vascular addressins and implicate NCCE in fundamental processes in cell specification and development.

Immunoglobulin family and carbohydrate vascular addressins encoded by Madcam1 and St6gal1 control lymphocyte homing into intestinal tissues, regulating immunity and inflammation. The addressins are developmentally programmed to decorate endothelial cells lining gut post-capillary and high endothelial venules (HEV), providing a prototypical example of organ- and segment-specific endothelial specialization. We identify conserved NKX-COUP-TFII composite elements (NCCE) in regulatory regions of Madcam1 and St6gal1 that bind intestinal homeodomain protein NKX2-3 cooperatively with venous nuclear receptor COUP-TFII to activate transcription. The Madcam1 element also integrates repressive signals from arterial/capillary Notch effectors. Pan-endothelial COUP-TFII overexpression induces ectopic addressin expression in NKX2-3 + capillaries, while NKX2-3 deficiency abrogates expression by HEV. Phylogenetically conserved NCCE are enriched in genes involved in neuron migration and morphogenesis of the heart, kidney, pancreas and other organs. Our results define an NKX-COUP-TFII morphogenetic code that targets expression of mucosal vascular addressins.

Single-cell transcriptomics promise to revolutionize our understanding of the vasculature. Emerging computational methods applied to high-dimensional single-cell data allow integration of results between samples and species and illuminate the diversity and underlying developmental and architectural organization of cell populations. Here, we illustrate these methods in the analysis of mouse lymph node (LN) lymphatic endothelial cells (LEC) at single-cell resolution. Clustering identifies five well-delineated subsets, including two medullary sinus subsets not previously recognized as distinct. Nearest neighbor alignments in trajectory space position the major subsets in a sequence that recapitulates the known features and suggests novel features of LN lymphatic organization, providing a transcriptional map of the lymphatic endothelial niches and of the transitions between them. Differences in gene expression reveal specialized programs for (1) subcapsular ceiling endothelial interactions with the capsule connective tissue and cells; (2) subcapsular floor regulation of lymph borne cell entry into the LN parenchyma and antigen presentation; and (3) pathogen interactions and (4) LN remodeling in distinct medullary subsets. LEC of the subcapsular sinus floor and medulla, which represent major sites of cell entry and exit from the LN parenchyma respectively, respond robustly to oxazolone inflammation challenge with enriched signaling pathways that converge on both innate and adaptive immune responses. Integration of mouse and human single-cell profiles reveals a conserved cross-species pattern of lymphatic vascular niches and gene expression, as well as specialized human subsets and genes unique to each species. The examples provided demonstrate the power of single-cell analysis in elucidating endothelial cell heterogeneity, vascular organization, and endothelial cell responses. We discuss the findings from the perspective of LEC functions in relation to niche formations in the unique stromal and highly immunological environment of the LN.

Abstract A critical limitation to cancer immunotherapy is posed by the paucity of anti-tumor T cells in tumor tissues, even after therapeutic intervention. Development of effective strategies to enhance T cell recruitment remains challenging. As a critical regulator of immune cell trafficking, the tumor vasculature is a promising target that can be utilized to enhance anti-tumor immunity. Functional vasculature requires specialization of endothelial cells (ECs): capillary ECs transport oxygen and nutrients to promote tumor growth, while venular ECs regulate the recruitment and extravasation of immune cells. The majority of the current vessel-targeting therapies are designed to deplete endothelial cells indiscriminately with the goal of starving tumor cells. Loss of venules as a consequence could further block sustained recruitment of anti-tumor T cells. An alternative strategy that instead promotes capillary-to-venule “reprogramming” could simultaneously inhibit the tumor-promoting activities of capillaries and preserve the T cell-recruiting functions of tumor vessels, and thus better augment anti-tumor immunity and benefit immunotherapies. Through single cell transcriptomic profiling of tumor ECs, we found the nuclear receptor Nr2f2 to be specifically expressed in tumor-associated venules but not in capillaries. Upon ectopic expression of Nr2f2 in tumor ECs, capillary vessels undergo fate switch and adopt the venular phenotype and functions, as confirmed by immune profiling and single cell transcriptomic analyses. Nr2f2-driven capillary-to-venule reprogramming enhanced the recruitment of cytotoxic T cells into the tumor tissue, and led to a significant reduction of tumor burden in mouse breast and pancreatic tumor models. Interestingly, Nr2f2-driven EC fate switch enhanced the anti-tumor efficacy of immunotherapies, including immune checkpoint blockade and adoptive cell therapy by transferring T cells specific for a surrogate tumor cell antigen. Collectively, these data suggest that strategies that reprogram tumor vessels from capillaries into venules can be exploited to enhance anti-tumor immune responses and sensitize tumors to immunotherapy, especially in immunologically cold tumors. Citation Format: Yu Zhu, Nicole Lazarus, Kevin Brulois, Nicole Salazar, Theresa Dinh, Junliang Pan, Eugene Butcher. Modulation of Nr2f2 reprograms tumor blood vessels to enhance anti-tumor immunity and immunotherapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1804.

Specialized stromal cells occupy and help define B- and T cell domains, which is crucial for proper functioning of our immune system. Signaling through lymphotoxin and TNF-receptors is crucial for development of different stromal subsets which are thought to arise from a common precursor. However, mechanisms that control the selective generation of the different stromal phenotypes are not known. Here we show that in mice, retinoic acid mediated signaling is important for the differentiation of precursors towards the Cxcl13pos follicular dendritic cell (FDC) lineage, while blocking lymphotoxin mediated Ccl19pos fibroblastic reticular cell (FRC) lineage differentiation. Consequently, we see at day of birth Cxcl13posCcl19neg/low and Cxcl13neg/lowCcl19pos cells within neonatal lymph nodes. Furthermore, ablation of retinoic acid receptor signaling in stromal precursors early after birth reduces Cxcl13 expression, while in addition, complete blockade of retinoic acid signaling prevents formation of FDC networks in lymph nodes.

The integrin α4β7 selectively regulates lymphocyte trafficking and adhesion in the gut and gut-associated lymphoid tissue (GALT). Here, we describe unexpected involvement of the tyrosine phosphatase Shp1 and the B cell lectin CD22 (Siglec-2) in the regulation of α4β7 surface expression and gut immunity. Shp1 selectively inhibited β7 endocytosis, enhancing surface α4β7 display and lymphocyte homing to GALT. In B cells, CD22 associated in a sialic acid–dependent manner with integrin β7 on the cell surface to target intracellular Shp1 to β7. Shp1 restrained plasma membrane β7 phosphorylation and inhibited β7 endocytosis without affecting β1 integrin. B cells with reduced Shp1 activity, lacking CD22 or expressing CD22 with mutated Shp1-binding or carbohydrate-binding domains displayed parallel reductions in surface α4β7 and in homing to GALT. Consistent with the specialized role of α4β7 in intestinal immunity, CD22 deficiency selectively inhibited intestinal antibody and pathogen responses. Lymphocyte homing to the gut and Peyer’s patches requires expression of integrin α4β7. Ballet and colleagues report that B cell expression of CD22 is required to specifically retain surface expression of β7 integrin molecules, thereby promoting B cell retention in the gut and optimal gut mucosal antibody responses.