Accumulation of tissue-resident natural killer cells, innate lymphoid cells, and CD8+ T cells towards the center of human lung tumors

Lung cancer is a leading cause of cancer-related death worldwide. Despite recent advances in tissue immunology, little is known about the spatial distribution of tissue-resident lymphocyte subsets in lung tumors. Using high-parameter flow cytometry, we identified an accumulation of tissue-resident lymphocytes including tissue-resident NK (trNK) cells and CD8+ tissue-resident memory T (TRM) cells toward the center of human non-small cell lung carcinomas (NSCLC). Chemokine receptor expression patterns indicated different modes of tumor-infiltration and/or residency between trNK cells and CD8+ TRM cells. In contrast to CD8+ TRM cells, trNK cells and ILCs generally expressed low levels of immune checkpoint receptors independent of location in the tumor. Additionally, granzyme expression in trNK cells and CD8+ TRM cells was highest in the tumor center, and intratumoral CD49a+CD16- NK cells were functional and responded stronger to target cell stimulation than their CD49a- counterparts, indicating functional relevance of trNK cells in lung tumors. In summary, the present spatial mapping of lymphocyte subsets in human NSCLC provides novel insights into the composition and functionality of tissue-resident immune cells, suggesting a role for trNK cells and CD8+ TRM cells in lung tumors and their potential relevance for future therapeutic approaches.

Comparison of Lung-Homing Receptor Expression and Activation Profiles on NK Cell and T Cell Subsets in COVID-19 and Influenza

Respiratory viral infections with SARS-CoV-2 and influenza viruses commonly induce a strong infiltration of immune cells into the human lung, with potential detrimental effects on the integrity of the lung tissue. Despite comprising the largest fractions of circulating lymphocytes in the lung, rather little is known about how peripheral blood natural killer (NK) cell and T cell subsets are equipped for lung-homing in COVID-19 and influenza. Here, we provide a detailed comparative analysis of NK cells and T cells in patients infected with SARS-CoV-2 or influenza virus, focusing on the protein and gene expression of chemokine receptors known to be involved in recruitment to the lung. For this, we used 28-colour flow cytometry as well as re-analysis of a publicly available single-cell RNA-seq dataset from bronchoalveolar lavage (BAL) fluid. Frequencies of NK cells and T cells expressing CXCR3, CXCR6, and CCR5 were altered in peripheral blood of COVID-19 and influenza patients, in line with increased transcript expression of CXCR3, CXCR6, and CCR5 and their respective ligands in BAL fluid. NK cells and T cells expressing lung-homing receptors displayed stronger phenotypic signs of activation compared to cells lacking lung-homing receptors, and activation was overall stronger in influenza compared to COVID-19. Together, our results indicate a role for CXCR3+, CXCR6+, and/or CCR5+ NK cells and T cells that potentially migrate to the lungs in moderate COVID-19 and influenza patients, identifying common targets for future therapeutic interventions in respiratory viral infections.

CD5 Surface Expression Marks Intravascular Human Innate Lymphoid Cells That Have a Distinct Ontogeny and Migrate to the Lung

Innate lymphoid cells (ILCs) contribute to immune defense, yet it is poorly understood how ILCs develop and are strategically positioned in the lung. This applies especially to human ILCs due to the difficulty of studying them in vivo. Here we investigated the ontogeny and migration of human ILCs in vivo with a humanized mouse model (“MISTRG”) expressing human cytokines. In addition to known tissue-resident ILC subsets, we discovered CD5-expressing ILCs that predominantly resided within the lung vasculature and in the circulation. CD5⁺ ILCs contained IFNγ-producing mature ILC1s as well as immature ILCs that produced ILC effector cytokines under polarizing conditions in vitro. CD5⁺ ILCs had a distinct ontogeny compared to conventional CD5^- ILCs because they first appeared in the thymus, spleen and liver rather than in the bone marrow after transplantation of MISTRG mice with human CD34⁺ hematopoietic stem and progenitor cells. Due to their strategic location, human CD5⁺ ILCs could serve as blood-borne sentinels, ready to be recruited into the lung to respond to environmental challenges. This work emphasizes the uniqueness of human CD5⁺ ILCs in terms of their anatomical localization and developmental origin compared to well-studied CD5^- ILCs.

Metastasis-associated macrophages constrain antitumor capability of natural killer cells in the metastatic site at least partially by membrane bound transforming growth factor β

BACKGROUND

Metastatic breast cancer is a leading cause of cancer-related death in women worldwide. Infusion of natural killer (NK) cells is an emerging immunotherapy for such malignant tumors, although elimination of the immunosuppressive tumor environment is required to improve its efficacy. The effects of this "metastatic" tumor environment on NK cells, however, remain largely unknown. Previous studies, including our own, have demonstrated that metastasis-associated macrophages (MAMs) are one of the most abundant immune cell types in the metastatic tumor niche in mouse models of metastatic breast cancer. We thus investigated the effects of MAMs on antitumor functions of NK cells in the metastatic tumor microenvironment.

METHODS

MAMs were isolated from the tumor-bearing lung of C57BL/6 mice intravenously injected with E0771-LG mouse mammary tumor cells. The effects of MAMs on NK cell cytotoxicity towards E0771-LG cells were evaluated in vitro by real-time fluorescence microscopy. The effects of MAM depletion on NK cell activation, maturation, and accumulation in the metastatic lung were evaluated by flow cytometry (CD69, CD11b, CD27) and in situ hybridization (Ncr1) using colony-stimulating factor 1 (CSF-1) receptor conditional knockout (Csf1r-cKO) mice. Finally, metastatic tumor loads in the chest region of mice were determined by bioluminescence imaging in order to evaluate the effect of MAM depletion on therapeutic efficacy of endogenous and adoptively transferred NK cells in suppressing metastatic tumor growth.

RESULTS

MAMs isolated from the metastatic lung suppressed NK cell-induced tumor cell apoptosis in vitro via membrane-bound transforming growth factor β (TGF-β) dependent mechanisms. In the tumor-challenged mice, depletion of MAMs increased the percentage of activated (CD69+) and mature (CD11b+CD27-) NK cells and the number of Ncr1+ NK cells as well as NK cell-mediated tumor rejection in the metastatic site. Moreover, MAM depletion or TGF-β receptor antagonist treatment significantly enhanced the therapeutic efficacy of NK cell infusion in suppressing early metastatic tumor outgrowth.

CONCLUSION

This study demonstrates that MAMs are a main negative regulator of NK cell function within the metastatic tumor niche, and MAM targeting is an attractive strategy to improve NK cell-based immunotherapy for metastatic breast cancer.

Natural killer cell immunotypes related to COVID-19 disease severity

Understanding innate immune responses in COVID-19 is important to decipher mechanisms of host responses and interpret disease pathogenesis. Natural killer (NK) cells are innate effector lymphocytes that respond to acute viral infections but might also contribute to immunopathology. Using 28-color flow cytometry, we here reveal strong NK cell activation across distinct subsets in peripheral blood of COVID-19 patients. This pattern was mirrored in scRNA-seq signatures of NK cells in bronchoalveolar lavage from COVID-19 patients. Unsupervised high-dimensional analysis of peripheral blood NK cells furthermore identified distinct NK cell immunotypes that were linked to disease severity. Hallmarks of these immunotypes were high expression of perforin, NKG2C, and Ksp37, reflecting increased presence of adaptive NK cells in circulation of patients with severe disease. Finally, arming of CD56bright NK cells was observed across COVID-19 disease states, driven by a defined protein-protein interaction network of inflammatory soluble factors. This study provides a detailed map of the NK cell activation landscape in COVID-19 disease.

Natural killer cell immunotypes related to COVID-19 disease severity

Understanding innate immune responses in COVID-19 is important to decipher mechanisms of host responses and interpret disease pathogenesis. Natural killer (NK) cells are innate effector lymphocytes that respond to acute viral infections but might also contribute to immunopathology. Using 28-color flow cytometry, we here reveal strong NK cell activation across distinct subsets in peripheral blood of COVID-19 patients. This pattern was mirrored in scRNA-seq signatures of NK cells in bronchoalveolar lavage from COVID-19 patients. Unsupervised high-dimensional analysis of peripheral blood NK cells furthermore identified distinct NK cell immunotypes that were linked to disease severity. Hallmarks of these immunotypes were high expression of perforin, NKG2C, and Ksp37, reflecting increased presence of adaptive NK cells in circulation of patients with severe disease. Finally, arming of CD56^bright NK cells was observed across COVID-19 disease states, driven by a defined protein-protein interaction network of inflammatory soluble factors. This study provides a detailed map of the NK cell activation landscape in COVID-19 disease.

Generation of mouse bone marrow-derived macrophages using tumor coculture assays to mimic the tumor microenvironment

Macrophages are one of the key immune cells within the tumor microenvironment that encourage the growth of tumors at the primary site as well as contributing to all parts of the metastatic cascade. Although it is possible to isolate macrophages directly from the tumor, this can be a laborious process and due to their plasticity, it is not possible to maintain their in vivo phenotype in vitro. For this reason, differentiating macrophages from bone marrow is an attractive alternative. Here we present robust methods to study in vitro derived macrophages including (i) the isolation and generation of macrophages from bone marrow, (ii) differentiation/characterization of classically activated, alternatively activated and tumor-conditioned macrophages, as well as (iii) in vitro co-culturing assays for tumor cell-macrophage interaction/transmigration.

Mammary Tumor Cells with High Metastatic Potential Are Hypersensitive to Macrophage-Derived HGF

Metastasis-associated macrophages (MAM) promote persistent growth of breast cancer cells at the metastatic site and are, thus, an attractive therapeutic target to treat breast cancer metastasis, a leading cause of cancer-related death in women. However, the precise mechanisms behind MAM-mediated metastatic tumor outgrowth have not been fully elucidated. Using mouse models of metastatic breast cancer, we showed that MAMs uniquely expressed hepatocyte growth factor (HGF) in metastatic tumors. We also demonstrated that a selected population of cancer cells with high metastatic potential (cancer cells that can establish metastatic tumors in mice with higher number and incidence than parental cells) had higher expression of HGF receptor, MNNG HOS transforming gene (MET), and were more responsive to HGF released from macrophages compared with the parental cells. Blockade of MET signaling in cancer cells suppressed metastatic tumor expansion, in part, through activation of natural killer cells. Results from this study suggest an approach to prevent life-threatening metastatic tumor formation using blockade of MAM-induced MET signal activation in metastatic cancer cells.

Abstract 2808: Investigating the role of macrophage-mediated suppression in the efficacy of NK cell immunotherapy for metastatic outgrowth of breast cancer cells

Breast cancer is the leading cause of cancer-related death in females worldwide. Although 5-year survival of breast cancer patients in early stages is 89-100%, that of patients with metastatic tumours is reduced to just 21%, suggesting the requirement of more effective therapies for metastatic breast cancer (MBC). As MBC is refractory to current therapies, NK cell infusion has been suggested as an alternative therapy. However, its efficacy is modest in MBC possibly due to the suppressive nature of the tumour microenvironment, especially through the tumour-associated macrophages (TAMs) within it. Here we investigated the effects of TAMs in metastatic tumours on NK cell cytotoxicity, as well as the mechanism behind TAM-mediated NK cell suppression.

To evaluate NK cell cytotoxicity, we established a method whereby mouse breast cancer cells were cultured with splenic NK cells, and the resultant tumour cell apoptosis was determined by quantitative fluorescence microscopy. To investigate the effects of TAMs on this NK cytotoxicity, we purified them from lungs with metastatic tumours and added them to this co-culture. We also investigated the suppressive effects of bone marrow-derived macrophages cultured with M-CSF (M-BMMs). To further investigate the mechanism, we depleted TAMs in mice with metastatic tumours and detected inhibitory receptor expression on NK cells as well as NK cell inhibitory ligands on TAMs in the metastatic lung and on M-BMMs by flow cytometry.

TAMs from metastatic tumours significantly reduced NK cell cytotoxicity toward tumour cells. M-BMMs (resembling TAMs) also reduced NK cell cytotoxicity. We also found that TAMs and M-BMMs expressed high levels of NK cell inhibitory ligands. There was no difference in the expression of inhibitory receptors on NK cells between tumour bearing lungs with or without TAMs.

To conclude, we have shown that TAMs in metastatic tumours, as well as their mimetic M-BMMs, can suppress NK cell cytotoxicity towards breast cancer cells in vitro. Our data suggest that TAMs express higher levels of inhibitory ligands and thereby transmit suppressive signals possibly through direct contact with NK cells. Further investigation of mechanisms behind TAM-mediated NK suppression might lead to the improvement of NK cell-based immunotherapy for MBC.

Citation Format: Demi Brownlie, Dahlia Doughty-Shenton, Jeffrey W. Pollard, Takanori Kitamura. Investigating the role of macrophage-mediated suppression in the efficacy of NK cell immunotherapy for metastatic outgrowth of breast cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2808.

The Atypical Chemokine Receptor Ackr2 Constrains NK Cell Migratory Activity and Promotes Metastasis

Chemokines have been shown to be essential players in a range of cancer contexts. In this study, we demonstrate that mice deficient in the atypical chemokine receptor Ackr2 display impaired development of metastasis in vivo in both cell line and spontaneous models. Further analysis reveals that this relates to increased expression of the chemokine receptor CCR2, specifically by KLRG1⁺ NK cells from the Ackr2^−/− mice. This leads to increased recruitment of KLRG1⁺ NK cells to CCL2-expressing tumors and enhanced tumor killing. Together, these data indicate that Ackr2 limits the expression of CCR2 on NK cells and restricts their tumoricidal activity. Our data have important implications for our understanding of the roles for chemokines in the metastatic process and highlight Ackr2 and CCR2 as potentially manipulable therapeutic targets in metastasis.

Monocytes Differentiate to Immune Suppressive Precursors of Metastasis-Associated Macrophages in Mouse Models of Metastatic Breast Cancer

Metastasis-associated macrophages (MAMs) play pivotal roles in breast cancer metastasis by promoting extravasation and survival of metastasizing cancer cells. In a metastatic breast cancer mouse model, we previously reported that circulating classical monocytes (C-MOs) preferentially migrated into the tumor-challenged lung where they differentiated into MAMs. However, the fate and characteristics of C-MOs in the metastatic site has not been defined. In this study, we identified that adoptively transferred C-MOs (F4/80^lowCD11b⁺Ly6C⁺) differentiated into a distinct myeloid cell population that is characterized as F4/80^highCD11b^highLy6C^high and gives rise to MAMs (F4/80^lowCD11b^highLy6C^low) within 18 h after migration into the metastatic lung. In mouse models of breast cancer, the CD11b^highLy6C^high MAM precursor cells (MAMPCs) were commonly found in the metastatic lung, and their accumulation was increased during metastatic tumor growth. The morphology and gene expression profile of MAMPCs were distinct from C-MOs and had greater similarity to MAMs. For example MAMPCs expressed mature macrophage markers such as CD14, CD36, CD64, and CD206 at comparable levels with MAMs, suggesting that MAMPCs have committed to a macrophage lineage in the tumor microenvironment. MAMPCs also expressed higher levels of Arg1, Hmox1, and Stab1 than C-MOs to a comparable level to MAMs. Expression of these MAM-associated genes in MAMPCs was reduced by genetic deletion of colony-stimulating factor 1 receptor (CSF1R). On the other hand, transient CSF1R blockade did not reduce the number of MAMPCs in the metastatic site, suggesting that CSF1 signaling is active in MAMPCs but is not required for their accumulation. Functionally MAMPCs suppressed the cytotoxicity of activated CD8⁺ T cells in vitro in part through superoxide production. Overall, our results indicate that immediately following migration into the metastatic tumors C-MOs differentiate into immunosuppressive cells that have characteristics of monocytic myeloid-derived suppressor cell phenotype and might be targeted to enhance efficacy of immunotherapy for metastatic breast cancer.