A neutrophil response linked to tumor control in immunotherapy.

Neutrophils accumulate in solid tumors, and their abundance correlates with poor prognosis. Neutrophils are not homogeneous, however, and could play different roles in cancer therapy. Here, we investigate the role of neutrophils in immunotherapy, leading to tumor control. We show that successful therapies acutely expanded tumor neutrophil numbers. This expansion could be attributed to a Sellhi state rather than to other neutrophils that accelerate tumor progression. Therapy-elicited neutrophils acquired an interferon gene signature, also seen in human patients, and appeared essential for successful therapy, as loss of the interferon-responsive transcription factor IRF1 in neutrophils led to failure of immunotherapy. The neutrophil response depended on key components of anti-tumor immunity, including BATF3-dependent DCs, IL-12, and IFNγ. In addition, we found that a therapy-elicited systemic neutrophil response positively correlated with disease outcome in lung cancer patients. Thus, we establish a crucial role of a neutrophil state in mediating effective cancer therapy.

Neutrophils in host defense, healing, and hypersensitivity: Dynamic cells within a dynamic host.

Neutrophils are cells of the innate immune system that are extremely abundant in vivo and respond quickly to infection, injury, and inflammation. Their constant circulation throughout the body makes them some of the first responders to infection, and indeed they play a critical role in host defense against bacterial and fungal pathogens. It is now appreciated that neutrophils also play an important role in tissue healing after injury. Their short life cycle, rapid response kinetics, and vast numbers make neutrophils a highly dynamic and potentially extremely influential cell population. It has become clear that they are highly integrated with other cells of the immune system and can thus exert critical effects on the course of an inflammatory response; they can further impact tissue homeostasis and recovery after challenge. In this review, we discuss the fundamentals of neutrophils in host defense and healing; we explore the relationship between neutrophils and the dynamic host environment, including circadian cycles and the microbiome; we survey the field of neutrophils in asthma and allergy; and we consider the question of neutrophil heterogeneity-namely, whether there could be specific subsets of neutrophils that perform different functions in vivo.

Macrophage-Targeted Therapy Unlocks Antitumoral Cross-talk between IFNγ-Secreting Lymphocytes and IL12-Producing Dendritic Cells.

Macrophages often abound within tumors, express colony-stimulating factor 1 receptor (CSF1R), and are linked to adverse patient survival. Drugs blocking CSF1R signaling have been used to suppress tumor-promoting macrophage responses; however, their mechanisms of action remain incompletely understood. Here, we assessed the lung tumor immune microenvironment in mice treated with BLZ945, a prototypical small-molecule CSF1R inhibitor, using single-cell RNA sequencing and mechanistic validation approaches. We showed that tumor control was not caused by CSF1R+ cell depletion; instead, CSF1R targeting reshaped the CSF1R+ cell landscape, which unlocked cross-talk between antitumoral CSF1R- cells. These cells included IFNγ-producing natural killer and T cells, and an IL12-producing dendritic cell subset, denoted as DC3, which were all necessary for CSF1R inhibitor-mediated lung tumor control. These data indicate that CSF1R targeting can activate a cardinal cross-talk between cells that are not macrophages and that are essential to mediate the effects of T cell-targeted immunotherapies and promote antitumor immunity.See related Spotlight by Burrello and de Visser, p. 4.

Versatile neutrophil functions in cancer.

Neutrophils have historically been considered a singular, terminally-differentiated cell population, replete with pre-formed granules, poised to react quickly, aggressively, and somewhat non-specifically in the face of a microbial challenge or tissue injury. However, in recent years, neutrophil biologists have started revisiting this simplistic conception. Many studies have identified complexities in neutrophil biology, and these findings have led the field to redefine neutrophil heterogeneity from multiple angles including their development and maturation, their tissue location, and their ability to respond to various (pathological) stimuli. In this review, we discuss the importance of this reassessment within the context of cancer. Experimental evidence supports that neutrophil behavior is diverse, context-dependent, and manipulable; cutting-edge technologies have enabled the identification of neutrophil heterogeneity with high resolution and in an unbiased manner, revealing what may be critical underpinnings of these diverse behaviors, and enabling sophisticated computational assessments of specific programs and interactions. We are coming ever closer to delineating a holistic picture of neutrophil heterogeneity and how it may interplay with cancer stage, tumor microenvironment, and therapy. All of this together paints a promising picture when considering how clinical practice may harness the heterogeneity of these cells, for biomarkers or therapeutic approaches, leveraging what we are learning about these powerful and plentiful immune effectors.

Resident Kupffer cells and neutrophils drive liver toxicity in cancer immunotherapy.

Immunotherapy is revolutionizing cancer treatment but is often restricted by toxicities. What distinguishes adverse events from concomitant antitumor reactions is poorly understood. Here, using anti-CD40 treatment in mice as a model of TH1-promoting immunotherapy, we showed that liver macrophages promoted local immune-related adverse events. Mechanistically, tissue-resident Kupffer cells mediated liver toxicity by sensing lymphocyte-derived IFN-γ and subsequently producing IL-12. Conversely, dendritic cells were dispensable for toxicity but drove tumor control. IL-12 and IFN-γ were not toxic themselves but prompted a neutrophil response that determined the severity of tissue damage. We observed activation of similar inflammatory pathways after anti-PD-1 and anti-CTLA-4 immunotherapies in mice and humans. These findings implicated macrophages and neutrophils as mediators and effectors of aberrant inflammation in TH1-promoting immunotherapy, suggesting distinct mechanisms of toxicity and antitumor immunity.

Leukocyte chemotactic receptor Fpr1 protects against aging-related posterior subcapsular cataract formation.

Cataracts are a common consequence of aging; however, pathogenesis remains poorly understood. Here, we observed that after 3 months of age mice lacking the G protein-coupled leukocyte chemotactic receptor Fpr1 (N-formyl peptide receptor 1) began to develop bilateral posterior subcapsular cataracts that progressed to lens rupture and severe degeneration, without evidence of either systemic or local ocular infection or inflammation. Consistent with this, Fpr1 was detected in both mouse and human lens in primary lens epithelial cells (LECs), the only cell type present in the lens; however, expression was confined to subcapsular LECs located along the anterior hemispheric surface. To maximize translucency, LECs at the equator proliferate and migrate posteriorly, then differentiate into lens fiber cells by nonclassical apoptotic signaling, which results in loss of nuclei and other organelles, including mitochondria which are a rich source of endogenous N-formyl peptides. In this regard, denucleation and posterior migration of LECs were abnormal in lenses from Fpr1-/- mice, and direct stimulation of LECs with the prototypic N-formyl peptide agonist fMLF promoted apoptosis. Thus, Fpr1 is repurposed beyond its immunoregulatory role in leukocytes to protect against cataract formation and lens degeneration during aging.

Tumor-Promoting Ly-6G+ SiglecFhigh Cells Are Mature and Long-Lived Neutrophils.

Myeloid cells co-expressing the markers CD11b, Ly-6G, and SiglecF can be found in large numbers in murine lung adenocarcinomas and accelerate cancer growth by fostering tumor cell invasion, angiogenesis, and immunosuppression; however, some of these cells' fundamental features remain unexplored. Here, we show that tumor-infiltrating CD11b+ Ly-6G+ SiglecFhigh cells are bona fide mature neutrophils and therefore differ from other myeloid cells, including SiglecFhigh eosinophils, SiglecFhigh macrophages, and CD11b+ Ly-6G+ myeloid-derived suppressor cells. We further show that SiglecFhigh neutrophils gradually accumulate in growing tumors, where they can live for several days; this lifespan is in marked contrast to that of their SiglecFlow counterparts and neutrophils in general, which live for several hours only. Together, these findings reveal distinct attributes for tumor-promoting SiglecFhigh neutrophils and help explain their deleterious accumulation in the tumor bed.

LTX-315 sequentially promotes lymphocyte-independent and lymphocyte-dependent antitumor effects.

LTX-315 is an oncolytic peptide that has antitumor efficacy in mice grafted with various tumor cell lines and is currently being tested in phase II clinical trials. Here we aimed to further evaluate LTX-315 in conditional genetic mouse models of cancer that typically resist current treatment options and to better understand the drug's mode of action in vivo. We report LTX-315 mediates profound antitumor effects against Braf- and Pten-driven melanoma and delays the progression of Kras- and P53-driven soft tissue sarcoma in mice. Additionally, we show in melanoma that LTX-315 triggers two sequential phases of antitumor response. The first phase of response, which begins within minutes of drug delivery into tumors, is defined by disrupted tumor vasculature and decreased tumor burden and occurs independently of lymphocytes. The second phase of response, which continues over weeks, is defined by long-term alteration of the tumor microenvironment; the changes induced by LTX-315 are most notably characterized by CD8+ T cell infiltration. We further show that these CD8+ T cells are involved in suppressing melanoma outgrowth in mice and report similar CD8+ T cell infiltration following LTX-315 treatment in melanoma and sarcoma patients. Taken together, these findings reveal LTX-315's multiple antitumor effects, including disrupting the tumor vasculature and promoting the conversion of poorly immunogenic tumors into ones that display antitumor T cell immunity.