Lymphatic vessels in the age of cancer immunotherapy

Lymphatic transport maintains homeostatic health and is necessary for immune surveillance, and yet lymphatic growth is often associated with solid tumour development and dissemination. Although tumour-associated lymphatic remodelling and growth were initially presumed to simply expand a passive route for regional metastasis, emerging research puts lymphatic vessels and their active transport at the interface of metastasis, tumour-associated inflammation and systemic immune surveillance. Here, we discuss active mechanisms through which lymphatic vessels shape their transport function to influence peripheral tissue immunity and the current understanding of how tumour-associated lymphatic vessels may both augment and disrupt antitumour immune surveillance. We end by looking forward to emerging areas of interest in the field of cancer immunotherapy in which lymphatic vessels and their transport function are likely key players: the formation of tertiary lymphoid structures, immune surveillance in the central nervous system, the microbiome, obesity and ageing. The lessons learnt support a working framework that defines the lymphatic system as a key determinant of both local and systemic inflammatory networks and thereby a crucial player in the response to cancer immunotherapy.

Metabolic targeting of cancer associated fibroblasts overcomes T-cell exclusion and chemoresistance in soft-tissue sarcomas

T cell-based immunotherapies have exhibited promising outcomes in tumor control; however, their efficacy is limited in immune-excluded tumors. Cancer-associated fibroblasts (CAFs) play a pivotal role in shaping the tumor microenvironment and modulating immune infiltration. Despite the identification of distinct CAF subtypes using single-cell RNA-sequencing (scRNA-seq), their functional impact on hindering T-cell infiltration remains unclear, particularly in soft-tissue sarcomas (STS) characterized by low response rates to T cell-based therapies. In this study, we characterize the STS microenvironment using murine models (in female mice) with distinct immune composition by scRNA-seq, and identify a subset of CAFs we termed glycolytic cancer-associated fibroblasts (glyCAF). GlyCAF rely on GLUT1-dependent expression of CXCL16 to impede cytotoxic T-cell infiltration into the tumor parenchyma. Targeting glycolysis decreases T-cell restrictive glyCAF accumulation at the tumor margin, thereby enhancing T-cell infiltration and augmenting the efficacy of chemotherapy. These findings highlight avenues for combinatorial therapeutic interventions in sarcomas and possibly other solid tumors. Further investigations and clinical trials are needed to validate these potential strategies and translate them into clinical practice.

Quantitative multiplex immunohistochemistry reveals inter-patient lymphovascular and immune heterogeneity in primary cutaneous melanoma

Introduction

Quantitative, multiplexed imaging is revealing complex spatial relationships between phenotypically diverse tumor infiltrating leukocyte populations and their prognostic implications. The underlying mechanisms and tissue structures that determine leukocyte distribution within and around tumor nests, however, remain poorly understood. While presumed players in metastatic dissemination, new preclinical data demonstrates that blood and lymphatic vessels (lymphovasculature) also dictate leukocyte trafficking within tumor microenvironments and thereby impact anti-tumor immunity. Here we interrogate these relationships in primary human cutaneous melanoma.

Methods

We established a quantitative, multiplexed imaging platform to simultaneously detect immune infiltrates and tumor-associated vessels in formalin-fixed paraffin embedded patient samples. We performed a discovery, retrospective analysis of 28 treatment-naïve, primary cutaneous melanomas.

Results

Here we find that the lymphvasculature and immune infiltrate is heterogenous across patients in treatment naïve, primary melanoma. We categorized five lymphovascular subtypes that differ by functionality and morphology and mapped their localization in and around primary tumors. Interestingly, the localization of specific vessel subtypes, but not overall vessel density, significantly associated with the presence of lymphoid aggregates, regional progression, and intratumoral T cell infiltrates.

Discussion

We describe a quantitative platform to enable simultaneous lymphovascular and immune infiltrate analysis and map their spatial relationships in primary melanoma. Our data indicate that tumor-associated vessels exist in different states and that their localization may determine potential for metastasis or immune infiltration. This platform will support future efforts to map tumor-associated lymphovascular evolution across stage, assess its prognostic value, and stratify patients for adjuvant therapy.

The tumor-draining lymph node as a reservoir for systemic immune surveillance

Early in solid tumor development, antigens are presented in tumor-draining lymph nodes (tdLNs), a process that is necessary to set up immune surveillance. Recent evidence indicates that tdLNs fuel systemic tumor-specific T cell responses which may halt cancer progression and facilitate future responses to immunotherapy. These protective responses, however, are subject to progressive dysfunction exacerbated by lymph node (LN) metastasis. We discuss emerging preclinical and clinical literature indicating that the tdLN is a crucial reservoir for systemic immunity that can potentiate immune surveillance. We also discuss the impact of LN metastasis and argue that a better understanding of the relationship between LN metastasis and systemic immunity will be necessary to direct regional disease management in the era of immunotherapy.

Lymph node metastasis: An immunological burden

Lymph node metastasis in breast cancer depends in part on the acquisition of an IFN-dependent, MHC-II+ state that induces regulatory T cell expansion and local immune suppression (Lei et al. 2023. J. Exp. Med.https://doi.org/10.1084/jem.20221847).

Lymphatic vessel transit seeds precursors to cytotoxic resident memory T cells in skin draining lymph nodes

Resident memory T cells (TRM) provide rapid, localized protection in peripheral tissues to pathogens and cancer. While TRM are also found in lymph nodes (LN), how they develop during primary infection and their functional significance remains largely unknown. Here, we track the anatomical distribution of anti-viral CD8+ T cells as they simultaneously seed skin and LN TRM using a model of skin infection with restricted antigen distribution. We find exquisite localization of LN TRM to the draining LN of infected skin. LN TRM formation depends on lymphatic transport and specifically egress of effector CD8+ T cells that appear poised for residence as early as 12 days post infection. Effector CD8+ T cell transit through skin is necessary and sufficient to populate LN TRM in draining LNs, a process reinforced by antigen encounter in skin. Importantly, we demonstrate that LN TRM are sufficient to provide protection against pathogenic rechallenge. These data support a model whereby a subset of tissue infiltrating CD8+ T cells egress during viral clearance, and establish regional protection in the draining lymphatic basin as a mechanism to prevent pathogen spread.

Structural Vulnerabilities in DLBCL for Enhanced Treatment Strategies

Diffuse large B-cell lymphoma (DLBCL) is a typically immune-suppressed lymphoma subtype with poor response to immune checkpoint blockade and chimeric antigen receptor T-cell therapy. Recent data demonstrated an association between an activated, myofibroblast-like tumor stroma with improved outcome. On the basis of these findings, Apollonio and colleagues explored the phenotypic, transcriptional, and functional state of fibroblastic reticular cells (FRC) in human and murine DLBCL. This study reveals that DLBCL cells trigger the activation and remodeling of FRCs, leading to a chronic inflammatory state that supports malignant B-cell survival. Transcriptional reprogramming of the FRCs may inhibit CD8+ T-cell migration and function through changes in homing chemokines, adhesion molecules, and antigen presentation machinery, which together limit the anti-DLBCL immune response. High-dimensional imaging mass cytometry revealed heterogeneous CD8+ T-cell and FRC neighborhoods that associated with different clinical outcomes and ex vivo modeling of the microenvironment indicated an opportunity to target the FRC network for improved T-cell motility, infiltration, and effector function. This research broadens our understanding of the complex interactions between the lymph node microarchitecture and antitumor immune surveillance, defines structural vulnerabilities in DLBCL, and thereby offers opportunities for combined therapeutic approaches.

Angiopoietin-2-dependent spatial vascular destabilization promotes T-cell exclusion and limits immunotherapy in melanoma

T cell position in the tumor microenvironment determines the probability of target encounter and tumor killing. CD8+ T cell exclusion from the tumor parenchyma is associated with poor response to immunotherapy, and yet the biology that underpins this distinct pattern remains unclear. Here we show that the vascular destabilizing factor angiopoietin-2 (ANGPT2) causes compromised vascular integrity in the tumor periphery, leading to impaired T cell infiltration to the tumor core. The spatial regulation of ANGPT2 in whole tumor cross-sections was analyzed in conjunction with T cell distribution, vascular integrity, and response to immunotherapy in syngeneic murine melanoma models. T cell exclusion was associated with ANGPT2 upregulation and elevated vascular leakage at the periphery of human and murine melanomas. Both pharmacological and genetic blockade of ANGPT2 promoted CD8+ T cell infiltration into the tumor core, exerting antitumor effects. Importantly, the reversal of T cell exclusion following ANGPT2 blockade not only enhanced response to anti-PD-1 immune checkpoint blockade therapy in immunogenic, therapy responsive mouse melanomas, but it also rendered non-responsive tumors susceptible to immunotherapy. Therapeutic response after ANGPT2 blockade, driven by improved CD8+ T cell infiltration to the tumor core, coincided with spatial TIE2 signaling activation and increased vascular integrity at the tumor periphery where endothelial expression of adhesion molecules was reduced. These data highlight ANGPT2/TIE2 signaling as a key mediator of T cell exclusion and a promising target to potentiate immune checkpoint blockade efficacy in melanoma.

Abstract 3511: Melanoma-shed, lymph-borne CSPG4 conditions the pre-metastatic lymph node niche

Tissues are primed for metastasis prior to the arrival of tumor cells. Primary tumors drive this transformation by shedding tumor-derived factors (TDFs), including extracellular vesicles and secreted/shed proteins (TSPs) into tumor-associated blood and lymphatic vasculature. Despite being the most common site of metastasis across solid tumor types, we know very little about how the lymph node (LN) is primed for metastasis by TDFs. Here, we test the hypothesis that lymph-borne TDFs are sufficient to initiate the formation of the pre-metastatic LN niche. Using a murine melanoma model (YUMM1.7), we demonstrate primary melanomas initiate remodeling in their draining LNs that enhances metastatic outgrowth relative to contralateral, non-draining and naïve LN controls. Furthermore, we have demonstrated that TDFs isolated from YUMM1.7-conditioned media uniquely activate this pro-metastatic LN phenotype rather than factors derived from benign dermis. The focus of this field has been on the role tumor-derived extracellular vesicles play in establishing this pre-metastatic niche, however our data further demonstrates TSPs are also sufficient to activate this niche. To identify candidate TDFs in vivo that have the potential to initiate LN transformation, we adopted a novel chemical biology strategy to ubiquitously tag TDFs in vivo using non-canonical amino acids and engineered expression of mutant tRNA synthetases in YUMM1.7 melanoma cells. Using this approach, we identified several TDFs by mass spectrometry present in pre-metastatic LNs, and identified one candidate (CSPG4; Melanoma-Associated Chondroitin Sulfate Proteoglycan) as a potential mediator of pre-metastatic niche development. Shed CSPG4 is found within TSPs isolated from media conditioned by YUMM1.7, but not benign dermal, cells. We generated stable shRNA-expressing YUMM1.7 cell lines for efficient knockdown of CSPG4, and found that loss of CSPG4 confers loss of TSP-dependent pre-metastatic niche development in the draining LN. Furthermore, using an enzyme specific to chondroitins (the main glycan decorating CSPG4), we demonstrate that loss of chondroitin glycosylation of CSPG4 is sufficient to attenuate metastasis, even with the core protein present. We find that fibroblastic reticular cells in the draining LN respond to TSPs by becoming more myofibroblast like, resembling cancer-associated fibroblasts that provide direct trophic support to tumor cells. This phenotypic switch is partially rescued in the absence of CSPG4. Our results collectively indicate TSPs prime the LN for metastasis and we have identified melanoma-shed CSPG4 as a driver of pre-metastatic niche development, potentially through its influence on the LN-resident fibroblasts.

Citation Format: Haley du Bois, Annie L. Chen, Katherine S. Ventre, Maria S. Steele, Triantafyllia Karakousi, Amanda W. Lund. Melanoma-shed, lymph-borne CSPG4 conditions the pre-metastatic lymph node niche [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3511.

T cell egress via lymphatic vessels is tuned by antigen encounter and limits tumor control

Antigen-specific CD8+ T cell accumulation in tumors is a prerequisite for effective immunotherapy, and yet the mechanisms of lymphocyte transit are not well defined. Here we show that tumor-associated lymphatic vessels control T cell exit from tumors via the chemokine CXCL12, and intratumoral antigen encounter tunes CXCR4 expression by effector CD8+ T cells. Only high-affinity antigen downregulates CXCR4 and upregulates the CXCL12 decoy receptor, ACKR3, thereby reducing CXCL12 sensitivity and promoting T cell retention. A diverse repertoire of functional tumor-specific CD8+ T cells, therefore, exit the tumor, which limits the pool of CD8+ T cells available to exert tumor control. CXCR4 inhibition or loss of lymphatic-specific CXCL12 boosts T cell retention and enhances tumor control. These data indicate that strategies to limit T cell egress might be an approach to boost the quantity and quality of intratumoral T cells and thereby response to immunotherapy.

CXCR6 promotes dermal CD8+ T cell survival and transition to long-term tissue residence

Tissue resident memory T cells (TRM) provide important protection against infection, and yet the interstitial signals necessary for their formation and persistence remain incompletely understood. Here we show that antigen-dependent induction of the chemokine receptor, CXCR6, is a conserved requirement for TRM formation in peripheral tissue after viral infection. CXCR6 was dispensable for the early accumulation of antigen-specific CD8+ T cells in skin and did not restrain their exit. Single cell sequencing indicated that CXCR6-/- CD8+ T cells were also competent to acquire a transcriptional program of residence but exhibited deficiency in multiple pathways that converged on survival and metabolic signals necessary for memory. As such, CXCR6-/- CD8+ T cells exhibited increased rates of apoptosis relative to controls in the dermis, leading to inefficient TRM formation. CXCR6 expression may therefore represent a common mechanism across peripheral non-lymphoid tissues and inflammatory states that increases the probability of long-term residence.

Single-cell RNA sequencing reveals the effects of chemotherapy on human pancreatic adenocarcinoma and its tumor microenvironment

The tumor microenvironment (TME) in pancreatic ductal adenocarcinoma (PDAC) is a complex ecosystem that drives tumor progression; however, in-depth single cell characterization of the PDAC TME and its role in response to therapy is lacking. Here, we perform single-cell RNA sequencing on freshly collected human PDAC samples either before or after chemotherapy. Overall, we find a heterogeneous mixture of basal and classical cancer cell subtypes, along with distinct cancer-associated fibroblast and macrophage subpopulations. Strikingly, classical and basal-like cancer cells exhibit similar transcriptional responses to chemotherapy and do not demonstrate a shift towards a basal-like transcriptional program among treated samples. We observe decreased ligand-receptor interactions in treated samples, particularly between TIGIT on CD8 + T cells and its receptor on cancer cells, and identify TIGIT as the major inhibitory checkpoint molecule of CD8 + T cells. Our results suggest that chemotherapy profoundly impacts the PDAC TME and may promote resistance to immunotherapy.

Abstract PR010: Single-cell sequencing elucidates the effects of chemotherapy on cancer cell heterogeneity and the tumor microenvironment of human pancreatic adenocarcinoma

The tumor microenvironment (TME) in pancreatic ductal adenocarcinoma (PDAC) is a complex ecosystem that drives tumor progression. Improving our understanding of the PDAC TME and its role in response to therapy via in-depth single cell characterization will have broad clinical implications for biomarker development and therapeutic design. In this study, we performed single-cell RNA sequencing on freshly collected human PDAC samples of primary (n=16) or metastatic (n=11) origin, either before (n=20) or after (n=7) chemotherapy. We found a heterogeneous mixture of basal and classical Moffitt cancer cell subtypes in all samples, along with distinct cancer-associated fibroblast (CAF) and tumor-associated macrophage (TAM) subpopulations. We identified the major CAF subpopulations as inflammatory CAFs (iCAFs) and myofibroblastic CAFs (myCAFs); within these subpopulations were a very few cells expressing immunogenic features which have previously been associated with antigen presenting CAFs (apCAFs). Tumor-associated macrophages (TAMs) could be categorized into two major subpopulations, C1QC+ TAMs or SPP1+ TAMs, each with distinct functional characteristics. For example, phagocytosis-associated gene sets were enriched in C1QC+ TAMs, while angiogenesis-associated gene sets were enriched in SPP1+ TAMs. Comparison of naïve and chemotherapy treated primary PDAC samples revealed that classical and basal-like cancer cells exhibited similar transcriptional responses to chemotherapy; this contrasts with some previous reports which posited a shift towards a basal-like transcriptional program among treated samples. We further noted that treated samples evinced fewer ligand-receptor interactions, particularly between TIGIT on CD8+ T cells and its ligand on cancer cells. We also identified TIGIT, not PD1, as the major inhibitory checkpoint molecule of CD8+ T cells in the PDAC TME. Altogether, our results suggest that chemotherapy impacts the PDAC TME and may further reduce response to immunotherapy.

Citation Format: Daniel Weissinger, Emily A. Kawaler, Gregor Werba, Ende Zhao, Despoina Kalfakakou, Surajit Dhara, Grace Oh, Xiaohong Jing, Nina Beri, Lauren Khanna, Tamas Gonda, Paul E. Oberstein, Cristina Hajdu, Cynthia Loomis, Adriana Heguy, Mara H. Sherman, Amanda W. Lund, Theodore H. Welling, Igor Dolgalev, Aristotelis Tsirigos, Diane M. Simeone. Single-cell sequencing elucidates the effects of chemotherapy on cancer cell heterogeneity and the tumor microenvironment of human pancreatic adenocarcinoma [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer; 2022 Sep 13-16; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2022;82(22 Suppl):Abstract nr PR010.

Perspectives in Melanoma: meeting report from the Melanoma Bridge (December 2nd - 4th, 2021, Italy)

Advances in immune checkpoint and combination therapy have led to improvement in overall survival for patients with advanced melanoma. Improved understanding of the tumor, tumor microenvironment and tumor immune-evasion mechanisms has resulted in new approaches to targeting and harnessing the host immune response. Combination modalities with other immunotherapy agents, chemotherapy, radiotherapy, electrochemotherapy are also being explored to overcome resistance and to potentiate the immune response. In addition, novel approaches such as adoptive cell therapy, oncogenic viruses, vaccines and different strategies of drug administration including sequential, or combination treatment are being tested. Despite the progress in diagnosis of melanocytic lesions, correct classification of patients, selection of appropriate adjuvant and systemic theràapies, and prediction of response to therapy remain real challenges in melanoma. Improved understanding of the tumor microenvironment, tumor immunity and response to therapy has prompted extensive translational and clinical research in melanoma. There is a growing evidence that genomic and immune features of pre-treatment tumor biopsies may correlate with response in patients with melanoma and other cancers, but they have yet to be fully characterized and implemented clinically. Development of novel biomarker platforms may help to improve diagnostics and predictive accuracy for selection of patients for specific treatment. Overall, the future research efforts in melanoma therapeutics and translational research should focus on several aspects including: (a) developing robust biomarkers to predict efficacy of therapeutic modalities to guide clinical decision-making and optimize treatment regimens, (b) identifying mechanisms of therapeutic resistance to immune checkpoint inhibitors that are potentially actionable, (c) identifying biomarkers to predict therapy-induced adverse events, and (d) studying mechanism of actions of therapeutic agents and developing algorithms to optimize combination treatments. During the Melanoma Bridge meeting (December 2nd-4th, 2021, Naples, Italy) discussions focused on the currently approved systemic and local therapies for advanced melanoma and discussed novel biomarker strategies and advances in precision medicine as well as the impact of COVID-19 pandemic on management of melanoma patients.

Immune Potential Untapped: Leveraging the Lymphatic System for Cancer Immunotherapy

Over the past decade, our understanding of the role of the lymphatic vasculature in tumor progression has evolved from it being a passive participant, as a first step along Halsted's path of sequential metastasis, to a potentially active regulator of antitumor immune surveillance. These new data, however, seemingly support paradoxical predictions for cancer immunotherapy; on one hand that enhanced lymphatic involvement augments antitumor immune surveillance and on the other, drives immune evasion and metastasis. The potential to leverage lymphatic biology for the benefit of clinical immunotherapy, therefore, requires a mechanistic understanding of how the lymphatic vasculature interacts with functional immune responses during disease progression and in the context of relevant immunotherapy regimes. In this review, I dissect the promise and challenge of engaging the lymphatic system for therapy and suggest important avenues for future investigation and potential application. See related article, p. 1041.

Lymph node metastasis fuels systemic disease

The functional impact of lymph node (LN) metastasis on systemic tumor progression has been a controversial question for decades. In their recent paper published in Cell, Reticker-Flynn et al. demonstrate that sequential evasion of natural killer (NK) cell control and interferon (IFN)-dependent epigenetic adaptation enhances the probability of LN metastasis. Further, they show that, once formed, LN metastases expand systemic peripheral tolerance and promote distant organ metastasis.

Cancer cell states recur across tumor types and form specific interactions with the tumor microenvironment

Transcriptional heterogeneity among malignant cells of a tumor has been studied in individual cancer types and shown to be organized into cancer cell states; however, it remains unclear to what extent these states span tumor types, constituting general features of cancer. Here, we perform a pan-cancer single-cell RNA-sequencing analysis across 15 cancer types and identify a catalog of gene modules whose expression defines recurrent cancer cell states including 'stress', 'interferon response', 'epithelial-mesenchymal transition', 'metal response', 'basal' and 'ciliated'. Spatial transcriptomic analysis linked the interferon response in cancer cells to T cells and macrophages in the tumor microenvironment. Using mouse models, we further found that induction of the interferon response module varies by tumor location and is diminished upon elimination of lymphocytes. Our work provides a framework for studying how cancer cell states interact with the tumor microenvironment to form organized systems capable of immune evasion, drug resistance and metastasis.

Standing Watch: Immune Activation and Failure in Melanoma Sentinel Lymph Nodes

An unbiased approach to map the sentinel lymph node landscape reveals progressive immune dysfunction associated with micrometastasis in patients with stage I-III cutaneous melanoma. Evidence of tumor-induced lymph node dysfunction may motivate new hypotheses for neoadjuvant therapy with potential to reinvigorate endogenous antitumor immunity. See related article by Yaddanapudi et al., p. 2069.

Be Easy and Chill: Melanoma Cells Tell Lymph Node Fibroblasts to Relax

Melanomas coopt tumor-draining lymph nodes to support metastatic potential and install immunosuppression. The specific mechanisms that mediate lymph node education, however, remain incompletely understood. In this issue, Rovera and colleagues describe the deactivation of contractile lymph node fibroblasts by dedifferentiated melanoma cells, leading to lymph node expansion and enhanced melanoma invasive potential. Fibroblastic reticular cell relaxation depended upon inhibition of constitutive JAK1/STAT3 and YAP/TAZ signaling, which was mediated in part by tumor secretion of the inflammatory cytokine, IL1. These data support an emerging hypothesis that intrinsic melanoma heterogeneity feeds forward to drive microenvironmental adaptations that mediate invasion and progression. See related article by Rovera et al., p. 1774.

Infection-induced lymphatic zippering restricts fluid transport and viral dissemination from skin

Lymphatic vessels are often considered passive conduits that flush antigenic material, pathogens, and cells to draining lymph nodes. Recent evidence, however, suggests that lymphatic vessels actively regulate diverse processes from antigen transport to leukocyte trafficking and dietary lipid absorption. Here we tested the hypothesis that infection-induced changes in lymphatic transport actively contribute to innate host defense. We demonstrate that cutaneous vaccinia virus infection by scarification activates dermal lymphatic capillary junction tightening (zippering) and lymph node lymphangiogenesis, which are associated with reduced fluid transport and cutaneous viral sequestration. Lymphatic-specific deletion of VEGFR2 prevented infection-induced lymphatic capillary zippering, increased fluid flux out of tissue, and allowed lymphatic dissemination of virus. Further, a reduction in dendritic cell migration to lymph nodes in the absence of lymphatic VEGFR2 associated with reduced antiviral CD8+ T cell expansion. These data indicate that VEGFR2-driven lymphatic remodeling is a context-dependent, active mechanism of innate host defense that limits viral dissemination and facilitates protective, antiviral CD8+ T cell responses.

CXCR6 is required for tissue resident memory T cell formation across diverse peripheral non-lymphoid tissues

CD8 T cell control of viral infections in peripheral tissues is largely dependent upon their spatial positioning. Clearance of pathogens requires direct contact between CD8 T cells and infected cells. Chemokine receptors play an essential role in this process by facilitating T cell entry into tissues, directing T cell positioning within tissues and by influencing egress out of tissues. Tissue resident memory T cells (TRM), which fail to egress after pathogen clearance and scan cells for signs of infection, are potent sources of immunity to secondary encounters with pathogens. Here we show that expression of the chemokine receptor CXCR6 is a conserved feature of TRM after viral infection in many non-lymphoid tissues. Using CXCR6KO TCR-tg T cells, we found that CXCR6 is necessary for proper formation of TRM in all non-lymphoid tissues examined. CXCR6 was necessary for early accumulation of effector T cells in several tissues such as the kidney and salivary gland but CXCR6 was dispensable for early accumulation in the skin. After vaccinia infection in the skin, CXCR6 expression is reinforced upon antigen re-encounter and promotes CD8 T cell accumulation in a migration-independent manner. Using single cell transcriptional analysis, we show that CXCR6KO TRM appear to exhibit a survival disadvantage and are outcompeted by wildtype T cells. This work reveals a critical requirement for generating TRM in diverse anatomical locations and may benefit strategies for vaccine design, anti-tumor immunity and reducing T-cell mediated autoimmunity.

Supported by R01CA238163 T32Al100853-10

Fluorescent tracking identifies key migratory dendritic cells in the lymph node after radiotherapy

Radiation therapy impacts all cells within the treatment field. Using novel technology, we track dendritic cells from the tumor to lymph nodes and demonstrate their importance in immune control of tumors.

Radiation therapy generates extensive cancer cell death capable of promoting tumor-specific immunity. Within the tumor, conventional dendritic cells (cDCs) are known to carry tumor-associated antigens to the draining lymph node (TdLN) where they initiate T-cell priming. How radiation influences cDC migration is poorly understood. Here, we show that immunological efficacy of radiation therapy is dependent on cDC migration in radioimmunogenic tumors. Using photoconvertible mice, we demonstrate that radiation impairs cDC migration to the TdLN in poorly radioimmunogenic tumors. Comparative transcriptional analysis revealed that cDCs in radioimmunogenic tumors express genes associated with activation of endogenous adjuvant signaling pathways when compared with poorly radioimmunogenic tumors. Moreover, an exogenous adjuvant combined with radiation increased the number of migrating cDCs in these poorly radioimmunogenic tumors. Taken together, our data demonstrate that cDC migration play a critical role in the response to radiation therapy.

Spatially mapping the immune landscape of melanoma using imaging mass cytometry

Melanoma is an immunogenic cancer with a high response rate to immune checkpoint inhibitors (ICIs). It harbors a high mutation burden compared with other cancers and, as a result, has abundant tumor-infiltrating lymphocytes (TILs) within its microenvironment. However, understanding the complex interplay between the stroma, tumor cells, and distinct TIL subsets remains a substantial challenge in immune oncology. To properly study this interplay, quantifying spatial relationships of multiple cell types within the tumor microenvironment is crucial. To address this, we used cytometry time-of-flight (CyTOF) imaging mass cytometry (IMC) to simultaneously quantify the expression of 35 protein markers, characterizing the microenvironment of 5 benign nevi and 67 melanomas. We profiled more than 220,000 individual cells to identify melanoma, lymphocyte subsets, macrophage/monocyte, and stromal cell populations, allowing for in-depth spatial quantification of the melanoma microenvironment. We found that within pretreatment melanomas, the abundance of proliferating antigen-experienced cytotoxic T cells (CD8⁺CD45RO⁺Ki67⁺) and the proximity of antigen-experienced cytotoxic T cells to melanoma cells were associated with positive response to ICIs. Our study highlights the potential of multiplexed single-cell technology to quantify spatial cell-cell interactions within the tumor microenvironment to understand immune therapy responses.

The lymphatic system and sentinel lymph nodes: conduit for cancer metastasis

The lymphatic system is a complicated system consisting of the lymphatic vessels and lymph nodes draining the extracellular fluid containing cellular debris, excess water and toxins to the circulatory system. The lymph nodes serve as a filter, thus, when the lymph fluid returns to the heart, it is completely sterile. In addition, the lymphatic system includes the mucosa-associated lymphoid tissue, such as tonsils, adenoids, Peyers patches in the small bowel and even the appendix. Taking advantage of the drainage system of the lymphatics, cancer cells enter the lymphatic vessels and then the lymph nodes. In general, the lymph nodes may serve as a gateway in the majority of cases in early cancer. Occasionally, the cancer cells may enter the blood vessels. This review article emphasizes the structural integrity of the lymphatic system through which cancer cells may spread. Using melanoma and breast cancer sentinel lymph node model systems, the spread of early cancer through the lymphatic system is progressive in a majority of cases. The lymphatic systems of the internal organs are much more complicated and difficult to study. Knowledge from melanoma and breast cancer spread to the sentinel lymph node may establish the basic principles of cancer metastasis. The goal of this review article is to emphasize the complexity of the lymphatic system. To date, the molecular mechanisms of cancer spread from the cancer microenvironment to the sentinel lymph node and distant sites are still poorly understood and their elucidation should take major priority in cancer metastasis research.

Tumor-draining lymph nodes: At the crossroads of metastasis and immunity

Early engagement of the lymphatic system by solid tumors in peripheral, nonlymphoid tissues is a clinical hallmark of cancer and often forecasts poor prognosis. The significance of lymph node metastasis for distant spread, however, has been questioned by large-scale lymph node dissection trials and the likely prevalence of direct hematogenous metastasis. Still, an emerging appreciation for the immunological role of the tumor-draining lymph node has renewed interest in its basic biology, role in metastatic progression, antitumor immunity, and patient outcomes. In this review, we discuss our current understanding of the early mechanisms through which tumors engage lymphatic transport and condition tumor-draining lymph nodes, the significance of these changes for both metastasis and immunity, and potential implications of the tumor-draining lymph node for immunotherapy.

Evolutionary predictability of genetic versus nongenetic resistance to anticancer drugs in melanoma

Therapy resistance arises from heterogeneous drug-tolerant persister cells or minimal residual disease (MRD) through genetic and nongenetic mechanisms. A key question is whether specific molecular features of the MRD ecosystem determine which of these two distinct trajectories will eventually prevail. We show that, in melanoma exposed to mitogen-activated protein kinase therapeutics, emergence of a transient neural crest stem cell (NCSC) population in MRD concurs with the development of nongenetic resistance. This increase relies on a glial cell line-derived neurotrophic factor-dependent signaling cascade, which activates the AKT survival pathway in a focal adhesion kinase (FAK)-dependent manner. Ablation of the NCSC population through FAK inhibition delays relapse in patient-derived tumor xenografts. Strikingly, all tumors that ultimately escape this treatment exhibit resistance-conferring genetic alterations and increased sensitivity to extracellular signal-regulated kinase inhibition. These findings identify an approach that abrogates the nongenetic resistance trajectory in melanoma and demonstrate that the cellular composition of MRD deterministically imposes distinct drug resistance evolutionary paths.

In Situ Tumor Vaccination with Nanoparticle Co-Delivering CpG and STAT3 siRNA to Effectively Induce Whole-Body Antitumor Immune Response

The success of immunotherapy with immune checkpoint inhibitors (ICIs) in a subset of individuals has been very exciting. However, in many cancers, responses to current ICIs are modest and are seen only in a small subsets of patients. Herein, a widely applicable approach that increases the benefit of ICIs is reported. Intratumoral administration of augmenting immune response and inhibiting suppressive environment of tumors-AIRISE-02 nanotherapeutic that co-delivers CpG and STAT3 siRNA-results in not only regression of the injected tumor, but also tumors at distant sites in multiple tumor model systems. In particular, three doses of AIRISE-02 in combination with systemic ICIs completely cure both treated and untreated aggressive melanoma tumors in 63% of mice, while ICIs alone do not cure any mice. A long-term memory immune effect is also reported. AIRISE-02 is effective in breast and colon tumor models as well. Lastly, AIRISE-02 is well tolerated in mice and nonhuman primates. This approach combines multiple therapeutic agents into a single nanoconstruct to create whole-body immune responses across multiple cancer types. Being a local therapeutic, AIRISE-02 circumvents regulatory challenges of systemic nanoparticle delivery, facilitating rapid translation to the clinic. AIRISE-02 is under investigational new drug (IND)-enabling studies, and clinical trials will soon follow.

Afferent Lymphatic Transport and Peripheral Tissue Immunity

Lymphatic vessels provide an anatomical framework for immune surveillance and adaptive immune responses. Although appreciated as the route for Ag and dendritic cell transport, peripheral lymphatic vessels are often not considered active players in immune surveillance. Lymphatic vessels, however, integrate contextual cues that directly regulate transport, including changes in intrinsic pumping and capillary remodeling, and express a dynamic repertoire of inflammatory chemokines and adhesion molecules that facilitates leukocyte egress out of inflamed tissue. These mechanisms together contribute to the course of peripheral tissue immunity. In this review, we focus on context-dependent mechanisms that regulate fluid and cellular transport out of peripheral nonlymphoid tissues to provide a framework for understanding the effects of afferent lymphatic transport on immune surveillance, peripheral tissue inflammation, and adaptive immunity.

Melanoma models for the next generation of therapies

There is a lack of appropriate melanoma models that can be used to evaluate the efficacy of novel therapeutic modalities. Here, we discuss the current state of the art of melanoma models including genetically engineered mouse, patient-derived xenograft, zebrafish, and ex vivo and in vitro models. We also identify five major challenges that can be addressed using such models, including metastasis and tumor dormancy, drug resistance, the melanoma immune response, and the impact of aging and environmental exposures on melanoma progression and drug resistance. Additionally, we discuss the opportunity for building models for rare subtypes of melanomas, which represent an unmet critical need. Finally, we identify key recommendations for melanoma models that may improve accuracy of preclinical testing and predict efficacy in clinical trials, to help usher in the next generation of melanoma therapies.

Building new roads to stronger immunity

A new cancer vaccine technology builds a network of local lymphatic vessels that paves the way to stronger responses to immunotherapy.

Computational Drug Repositioning Identifies Statins as Modifiers of Prognostic Genetic Expression Signatures and Metastatic Behavior in Melanoma

Despite advances in melanoma treatment, more than 70% of patients with distant metastasis die within 5 years. Proactive treatment of early melanoma to prevent metastasis could save lives and reduce overall healthcare costs. Currently, there are no treatments specifically designed to prevent early melanoma from progressing to metastasis. We used the Connectivity Map to conduct an in silico drug screen and identified 3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitors (statins) as a drug class that might prevent melanoma metastasis. To confirm the in vitro effect of statins, RNA sequencing was completed on A375 cells after treatment with fluvastatin to describe changes in the melanoma transcriptome. Statins induced differential expression in genes associated with metastasis and are used in commercially available prognostic tests for melanoma metastasis. Finally, we completed a chart review of 475 patients with melanoma. Patients taking statins were less likely to have metastasis at the time of melanoma diagnosis in both univariate and multivariate analyses (24.7% taking statins vs. 37.6% not taking statins, absolute risk reduction = 12.9%, P = 0.038). These findings suggest that statins might be useful as a treatment to prevent melanoma metastasis. Prospective trials are required to verify our findings and to determine the mechanism of metastasis prevention.

SITC cancer immunotherapy resource document: a compass in the land of biomarker discovery

Since the publication of the Society for Immunotherapy of Cancer's (SITC) original cancer immunotherapy biomarkers resource document, there have been remarkable breakthroughs in cancer immunotherapy, in particular the development and approval of immune checkpoint inhibitors, engineered cellular therapies, and tumor vaccines to unleash antitumor immune activity. The most notable feature of these breakthroughs is the achievement of durable clinical responses in some patients, enabling long-term survival. These durable responses have been noted in tumor types that were not previously considered immunotherapy-sensitive, suggesting that all patients with cancer may have the potential to benefit from immunotherapy. However, a persistent challenge in the field is the fact that only a minority of patients respond to immunotherapy, especially those therapies that rely on endogenous immune activation such as checkpoint inhibitors and vaccination due to the complex and heterogeneous immune escape mechanisms which can develop in each patient. Therefore, the development of robust biomarkers for each immunotherapy strategy, enabling rational patient selection and the design of precise combination therapies, is key for the continued success and improvement of immunotherapy. In this document, we summarize and update established biomarkers, guidelines, and regulatory considerations for clinical immune biomarker development, discuss well-known and novel technologies for biomarker discovery and validation, and provide tools and resources that can be used by the biomarker research community to facilitate the continued development of immuno-oncology and aid in the goal of durable responses in all patients.

Lymph: (Fe)rrying Melanoma to Safety

Lymph nodes are typically the first clinically detectable site of metastasis in melanoma, but the mechanisms that determine this preference are not well understood. An article in Nature reports that the unique composition of lymph may protect melanoma cells from ferroptosis-a form of iron-dependent cell death, thereby increasing metastatic efficiency.

HMGB1 Promotes Myeloid Egress and Limits Lymphatic Clearance of Malignant Pleural Effusions

Pleural effusions, when benign, are attributed to cardiac events and suffusion of fluid within the pleural space. When malignant, lymphatic obstruction by tumor and failure to absorb constitutively produced fluid is the predominant formulation. The prevailing view has been challenged recently, namely that the lymphatics are only passive vessels, carrying antigenic fluid to secondary lymphoid sites. Rather, lymphatic vessels can be a selective barrier, efficiently coordinating egress of immune cells and factors within tissues, limiting tumor spread and immune pathology. An alternative explanation, offered here, is that damage associated molecular pattern molecules, released in excess, maintain a local milieu associated with recruitment and retention of immune cells associated with failed lymphatic clearance and functional lymphatic obstruction. We found that levels of high mobility group box 1 (HMGB1) were equally elevated in both benign and malignant pleural effusions (MPEs) and that limited diversity of T cell receptor expressing gamma and delta chain were inversely associated with these levels in MPEs. Acellular fluid from MPEs enhanced γδ T cell proliferation in vitro, while inhibiting cytokine production from γδ T cells and monocytes as well as restricting monocyte chemotaxis. Novel therapeutic strategies, targeting HMGB1 and its neutralization in such effusions as well as direct delivery of immune cells into the pleural space to reconstitute normal physiology should be considered.

Abstract A78: IFNg-activated lymphatic vessels express PD-L1 and suppress effector T-cell function in melanoma

Peripheral tissues adopt mechanisms of immune suppression that counteract protective immunity to prevent immunopathology and are co-opted by tumors for immune escape. In tumors, cytotoxic, antigen-specific T cells produce IFNg and activate multiple mechanisms of adaptive immune resistance, including upregulation of the T-cell inhibitory molecule programed death ligand 1 (PD-L1). Tumor cell PD-L1 expression does not predict response to anti-PD-L1 immunotherapy, indicating, however, that other sources of PD-L1 in tumor microenvironments may contribute to PD-L1-dependent immune suppression. Lymphatic vessels facilitate antigen and dendritic cell transport to draining lymph nodes and are required for antitumor immunity. Interestingly, lymphatic endothelial cells in lymph nodes are tolerogenic at steady-state and constitutively express PD-L1 to delete self-reactive CD8+ T cells. However, whether lymphatic endothelial cells in tumor microenvironments are also directly immunosuppressive remains unclear. Here we test the hypothesis that peripheral, tumor-associated lymphatic vessels acquire immunosuppressive mechanisms, e.g., PD-L1 expression, that limit effector CD8+ T-cell accumulation and function in melanoma. We demonstrate that host nonhematopoietic, nontumor, PD-L1 limits CD8+ T-cell accumulation in murine melanoma. Further, we show that tumor-associated lymphatic endothelial cells upregulate PD-L1 in response to IFNg produced by tumor-infiltrating, antigen-specific CD8+ T cells. As such, loss of IFNgR by lymphatic endothelial cells improves CD8+ T-cell accumulation in murine melanomas, thereby enhancing tumor control and improved overall survival. Importantly, this robust lymphatic vessel-dependent tumor control was revealed in the context of murine melanomas with significant UVB-induced somatic mutation burden, consistent with a cytotoxic T cell-mediated negative feedback mechanism. Consequently, we present IFNg-mediated activation of tumor-associated lymphatic vessels as a new component of adaptive immune resistance, suggesting that context-dependent lymphatic vessel function may provide novel, targetable mechanisms of immune control in melanoma.

Citation Format: Ryan S. Lane, Alec P. Breazeale, Amanda W. Lund. IFNg-activated lymphatic vessels express PD-L1 and suppress effector T-cell function in melanoma [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2018 Nov 27-30; Miami Beach, FL. Philadelphia (PA): AACR; Cancer Immunol Res 2020;8(4 Suppl):Abstract nr A78.

Abstract IA19: Lymphatic vessels: Barriers to adaptive immunity in melanoma

Mechanisms of immune suppression in peripheral tissues counteract protective immunity to prevent immunopathology and are co-opted by tumors for immune escape. Nonhematopoietic cells, as the resident tissue scaffold, play critical roles in regulating the infiltration, retention, function, and exit of tissue- and tumor-infiltrating leukocytes. While lymphatic vessels facilitate T-cell priming through dendritic cell and antigen delivery to lymph nodes, they also facilitate regional metastasis and exert multiple immune-suppressive mechanisms that maintain peripheral tolerance in steady state lymph nodes. We hypothesized that in tumors peripheral lymphatic vessels exhibit context-dependent function that limits local effector CD8+ T-cell accumulation in melanoma. Our work demonstrates that lymphatic vessels both maintain homeostatic mechanisms of peripheral tolerance in poorly inflamed tumors to limit immune surveillance and activate mechanisms of adaptive immune resistance in the context of potent cytotoxic T-cell activity. Consequently, we present tumor-associated lymphatic vessels as a new, anatomic immune checkpoint in melanoma. Our work suggests that understanding context-dependent lymphatic vessel function will continue to reveal novel mechanisms of immune control and metastasis that may be targeted for therapeutic response.

Citation Format: Amanda W. Lund. Lymphatic vessels: Barriers to adaptive immunity in melanoma [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2018 Nov 27-30; Miami Beach, FL. Philadelphia (PA): AACR; Cancer Immunol Res 2020;8(4 Suppl):Abstract nr IA19.

The Biophysics of Lymphatic Transport: Engineering Tools and Immunological Consequences

Lymphatic vessels mediate fluid flows that affect antigen distribution and delivery, lymph node stromal remodeling, and cell-cell interactions, to thus regulate immune activation. Here we review the functional role of lymphatic transport and lymph node biomechanics in immunity. We present experimental tools that enable quantitative analysis of lymphatic transport and lymph node dynamics in vitro and in vivo. Finally, we discuss the current understanding for how changes in lymphatic transport and lymph node biomechanics contribute to pathogenesis of conditions including cancer, aging, neurodegeneration, and infection.

Winter is coming: Tumor cells go into hibernation

In response to hypoxia in the primary tumor microenvironment, tumor cells induce a state of dormancy enabling their persistence at metastatic sites and resistance to therapy.

Quantifying Leukocyte Egress via Lymphatic Vessels from Murine Skin and Tumors

Leukocyte egress from peripheral tissues to draining lymph nodes is not only critical for immune surveillance and initiation but also contributes to the resolution of peripheral tissue responses. While a variety of methods are used to quantify leukocyte egress from non-lymphoid, peripheral tissues, the cellular and molecular mechanisms that govern context-dependent egress remain poorly understood. Here, we describe the use of in situ photoconversion for quantitative analysis of leukocyte egress from murine skin and tumors. Photoconversion allows for the direct labeling of leukocytes resident within cutaneous tissue. Though skin exposure to violet light induces local inflammatory responses characterized by leukocyte infiltrates and vascular leakiness, in a head-to-head comparison with transdermal application of fluorescent tracers, photoconversion specifically labeled migratory dendritic cell populations and simultaneously enabled the quantification of myeloid and lymphoid egress from cutaneous microenvironments and tumors. The mechanisms of leukocyte egress remain a missing component in our understanding of intratumoral leukocyte complexity, and thus the application of the tools described herein will provide unique insight into the dynamics of tumor immune microenvironments both at steady state and in response to therapy.

IFNγ-activated dermal lymphatic vessels inhibit cytotoxic T cells in melanoma and inflamed skin

Mechanisms of immune suppression in peripheral tissues counteract protective immunity to prevent immunopathology and are coopted by tumors for immune evasion. While lymphatic vessels facilitate T cell priming, they also exert immune suppressive effects in lymph nodes at steady-state. Therefore, we hypothesized that peripheral lymphatic vessels acquire suppressive mechanisms to limit local effector CD8+ T cell accumulation in murine skin. We demonstrate that nonhematopoietic PD-L1 is largely expressed by lymphatic and blood endothelial cells and limits CD8+ T cell accumulation in tumor microenvironments. IFNγ produced by tissue-infiltrating, antigen-specific CD8+ T cells, which are in close proximity to tumor-associated lymphatic vessels, is sufficient to induce lymphatic vessel PD-L1 expression. Disruption of IFNγ-dependent crosstalk through lymphatic-specific loss of IFNγR boosts T cell accumulation in infected and malignant skin leading to increased viral pathology and tumor control, respectively. Consequently, we identify IFNγR as an immunological switch in lymphatic vessels that balances protective immunity and immunopathology leading to adaptive immune resistance in melanoma.

Non-hematopoietic Control of Peripheral Tissue T Cell Responses: Implications for Solid Tumors

In response to pathological challenge, the host generates rapid, protective adaptive immune responses while simultaneously maintaining tolerance to self and limiting immune pathology. Peripheral tissues (e.g., skin, gut, lung) are simultaneously the first site of pathogen-encounter and also the location of effector function, and mounting evidence indicates that tissues act as scaffolds to facilitate initiation, maintenance, and resolution of local responses. Just as both effector and memory T cells must adapt to their new interstitial environment upon infiltration, tissues are also remodeled in the context of acute inflammation and disease. In this review, we present the biochemical and biophysical mechanisms by which non-hematopoietic stromal cells and extracellular matrix molecules collaborate to regulate T cell behavior in peripheral tissue. Finally, we discuss how tissue remodeling in the context of tumor microenvironments impairs T cell accumulation and function contributing to immune escape and tumor progression.

Characterization of dural sinus-associated lymphatic vasculature in human Alzheimer's dementia subjects

Recent reports describing lymphatic vasculature in the meninges have challenged the traditional understanding of interstitial solute clearance from the central nervous system, although the significance of this finding in human neurological disease remains unclear. To begin to define the role of meningeal lymphatic function in the clearance of interstitial amyloid beta (Aβ), and the contribution that its failure may make to the development of Alzheimer's disease (AD), we examined meningeal tissue from a case series including AD and control subjects by confocal microscopy. Our findings confirm the presence of lymphatic vasculature in the human meninges and indicate that, unlike perivascular efflux pathways in the brain parenchyma in subjects with AD, Aβ is not deposited in or around meningeal lymphatic vessels associated with dural sinuses. Our findings demonstrate that while the meningeal lymphatic vasculature may serve as an efflux route for Aβ from the brain and cerebrospinal fluid, Aβ does not deposit in the walls of meningeal lymphatic vessels in the setting of AD.

Toward Minimal Residual Disease-Directed Therapy in Melanoma

Many patients with advanced cancers achieve dramatic responses to a panoply of therapeutics yet retain minimal residual disease (MRD), which ultimately results in relapse. To gain insights into the biology of MRD, we applied single-cell RNA sequencing to malignant cells isolated from BRAF mutant patient-derived xenograft melanoma cohorts exposed to concurrent RAF/MEK-inhibition. We identified distinct drug-tolerant transcriptional states, varying combinations of which co-occurred within MRDs from PDXs and biopsies of patients on treatment. One of these exhibited a neural crest stem cell (NCSC) transcriptional program largely driven by the nuclear receptor RXRG. An RXR antagonist mitigated accumulation of NCSCs in MRD and delayed the development of resistance. These data identify NCSCs as key drivers of resistance and illustrate the therapeutic potential of MRD-directed therapy. They also highlight how gene regulatory network architecture reprogramming may be therapeutically exploited to limit cellular heterogeneity, a key driver of disease progression and therapy resistance.