NK cells and missing self recognition : genetic control, mhc class i dependent education and potential use in cancer therapy

NK cells belong to the innate immune system and are important in the defense against virus infections and malignant cells. They mediate their effector functions via release of cytotoxic granules and by cytokine production which can influence the status of other (immune) cells. NK cells are regulated by germline encoded receptors, both activating and inhibitory, recognizing molecules that are induced upon infection or cellular stress and self ligands respectively. Ly49 receptors (Ly49r) make up the largest NK cell receptor family in mice. It contains both activating and inhibitory receptors most of which bind to major histocompatibility complex class I (MHC I) molecules. NK cells patrol tissues and inspect surrounding cells for alterations in activating ligands and MHC I expression, balancing the input for decision of response. If the activation exceeds the inhibition, the target cell is eliminated. This ability to sense loss of self MHC I is referred to as missing self recognition. It can be directed against virus infected cells and tumor cells which often downmodulate MHC I, while they upregulate activating ligands. NK cells are educated via Ly49r-MHC I interactions to ensure self-tolerance and reactivity against aberrant cells. MHC I dependent education influences the NK cell population in at least two ways; modulation of responsiveness of each cell and skewing of the inhibitory receptor repertoire, i e the frequencies of NK cells expressing different combinations of Ly49r. The main aim of this thesis has been to study missing self recognition and MHC I dependent NK cell education and how these phenomena are influenced by different factors. In paper I, we characterized a genetic defect leading to Impaired Missing Self Recognition, in a mouse strain that we have termed IMSR mice. These mice had originally been developed by targeting a non-classical MHC gene, but the defect and the IMSR defect segregated independently. The IMSR mice were found to have a normal number of NK cells, which retained some functions, while missing self rejection and some activation pathways were partly or completely impaired. This defect was found to be NK cell intrinsic; it was not due to total lack of inhibitory receptors function, nor lack of MHC dependent education. In paper II and III we investigated how NK cells respond to altered inhibitory input from the environment in the host. Antibody mediated inhibitory receptor blockade was used as a tool to reduce the inhibitory input, which led to two different effects on the targeted NK cell populations 1) increased in vivo elimination of MHC I+ tumor cells without breaking tolerance towards normal healthy cells (paper II) and 2) induction of hyporesponsiveness i e reduced in vitro responsiveness or reduced capacity to eliminate MHC I- spleen cells. Importantly, elimination of MHC I- tumor cells was maintained. This was also investigated in an adoptive transfer model where the NK cell responsiveness could be either increased or reduced, depending on the MHC I expression in the recipient host (paper III). In conclusion, we found that NK cells can retune their responsiveness upon altered inhibitory input, but that responsiveness levels are adapted to healthy cells, still allowing efficient killing of tumor cells of the same missing self phenotype. In paper IV, we investigated whether skewing of the inhibitory receptor repertoire occurs already during NK cell development, before they reach the blood and the spleen. We found that the process leading to overrepresentation of NK cells expressing only one self MHC receptor is initiated during in the bone marrow already at the first NK cell developmental stage where inhibitory Ly49 receptors are expressed. This is most probably influenced both by selective proliferation and apoptosis

Interleukin-33 is a Novel Immunosuppressor that Protects Cancer Cells from TIL Killing by a Macrophage-Mediated Shedding Mechanism

Recognition of specific antigens expressed in cancer cells is the initial process of cytolytic T cell-mediated cancer killing. However, this process can be affected by other non-cancerous cellular components in the tumor microenvironment. Here, it is shown that interleukin-33 (IL-33)-activated macrophages protect melanoma cells from tumor-infiltrating lymphocyte-mediated killing. Mechanistically, IL-33 markedly upregulates metalloprotease 9 (MMP-9) expression in macrophages, which acts as a sheddase to trim NKG2D, an activating receptor expressed on the surface of natural killer (NK) cells, CD8+ T cells, subsets of CD4+ T cells, iNKT cells, and gamma delta T cells. Further, MMP-9 also cleaves the MHC class I molecule, cell surface antigen-presenting complex molecules, expressed in melanoma cells. Consequently, IL-33-induced macrophage MMP-9 robustly mitigates the tumor killing-effect by T cells. Genetic and pharmacological loss-of-function of MMP-9 sheddase restore T cell-mediated cancer killing. Together, these data provide compelling in vitro and in vivo evidence showing novel mechanisms underlying the IL-33-macrophage-MMP-9 axis-mediated immune tolerance against cancer cells. Targeting each of these signaling components, including IL-33 and MMP-9 provides a new therapeutic paradigm for improving anticancer efficacy by immune therapy.Funding Agencies|European Research Council (ERC) advanced grant ANGIOFATEuropean Research Council (ERC) [250021]; Swedish Research CouncilSwedish Research CouncilEuropean Commission; Swedish Cancer Foundation; Swedish Childrens Cancer Foundation; Strategic Research Areas (SFO)-Stem Cell and Regenerative Medicine Foundation; Karolinska Institute FoundationKarolinska Institutet; Karolinska Institute distinguished professor awardKarolinska Institutet; Torsten Soderbergs Foundation; Maud and Birger Gustavsson Foundation; NOVO Nordisk Foundation-Advance grantNovo Nordisk; NOVO Nordisk FoundationNovo Nordisk Foundation; Knut and Alice Wallenbergs FoundationKnut &amp; Alice Wallenberg Foundation; National Natural Science Foundation of ChinaNational Natural Science Foundation of China (NSFC) [81801163, 81703617]; Jinan clinical medical science and technology innovation plan [202019099]; China Scholarship CouncilChina Scholarship Council [201906225024]; Karolinska InstituteKarolinska Institutet</p