Natural Killer Cell-mediated Rejection Research Articles

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

BackgroundMetastatic 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...

NK Cell Alloreactivity against KIR-Ligand-Mismatched HLA-Haploidentical Tissue Derived from HLA Haplotype-Homozygous iPSCs.

SummaryHLA haplotype-homozygous (HLA-homo) induced pluripotent stem cells (iPSCs) are being prepared to be used for allogeneic transplantation of regenerated tissue into recipients carrying an identical haplotype in one of the alleles (HLA-hetero). However, it remains unaddressed whether natural killer (NK) cells respond to these regenerated cells. HLA-C allotypes, known to serve as major ligands for inhibitory receptors of NK cells, can be classified into group 1 (C1) and group 2 (C2), based on their binding specificities. We found that the T cells and vascular endothelial cells regenerated from HLA-homo-C1/C1 iPSCs were killed by specific NK cell subsets from a putative HLA-hetero-C1/C2 recipient. Such cytotoxicity was canceled when target cells were regenerated from iPSCs transduced with the C2 gene identical to the recipient. These results clarify that NK cells can kill regenerated cells by sensing the lack of HLA-C expression and further provide the basis for an approach to prevent such NK cell-mediated rejection responses.

Rapid Increase of Interleukin-10 Plasma Levels After Combined Auxiliary Liver-Kidney Transplantation in Presensitized Patients

After transplantation, donor dendritic cells (DCs) in the grafted organ are activated by an ischemia/reperfusion-induced inflammatory process that induces their migration to the recipient's secondary lymphoid tissues. The subsequent interaction between migrated and mature donor DCs, recipient T cells, and natural killer (NK) cells is proposed to be crucial in directing host immune reactions toward allograft rejection. A liver transplant is less prone to induce rejection compared with most other solid organ transplants, and simultaneous transplantation of liver and kidney is known to improve the clinical outcome of kidney transplantation. Here we show that liver as well as combined auxiliary liver-kidney transplantation in patients induces a rapid increase in plasma interleukin-10 (IL-10) to levels that are significantly higher than those seen after standard kidney transplantation. Addition of IL-10 during in vitro maturation of human monocyte-derived DCs with ischemia/reperfusion-associated factors was found to affect phenotypic DC maturation significantly. Addition of IL-10 inhibited DC production of the NK cell- and T cell-recruiting chemokines CXCL9, CXCL10 and CXCL11. Our findings indicate that liver transplantation induces a substantial systemic release of IL-10, which may inhibit T cell- and NK cell-mediated rejection processes toward the transplanted liver and concurrently transplanted kidney.

Tumor Defense Systems Using <i>O</i>-Glycans

During the process of hematogenous tumor metastasis, tumor cells that dissociated from the primary site enter the blood vessels and are exposed to innate immune systems in host blood circulation. In the innate immune systems, natural killer (NK) cells play a major role in rejecting tumors and suppressing metastasis. To establish metastasis, tumor cells therefore need to defend themselves against tumor rejection by NK cells. It has been recently discovered that some tumor cells develop defense systems against NK cell attack using certain types of cell-surface carbohydrates. The types of carbohydrates attached to cell-surface glycoproteins through serine or threonine residues contain a branch consisting of β-1,6-linkage of N-acetylglucosamine and N-acetylgalactosamine and are designated as core2 O-glycans. Tumor cells expressing core2 O-glycans evade NK cell-mediated tumor rejection, thereby surviving longer in host circulation and acquiring high-metastatic phenotypes. This review explains two types of tumor defense systems against NK cell immunity using core2 O-glycans.

The basis and value of currently used immunomodulatory therapies in recurrent miscarriage

Recurrent miscarriage (RM) without an obvious identifiable cause may arise from excessive maternal T and natural killer (NK) cell activity against the trophoblast or early embryo. Impaired regulatory T cell function leading to increased pro-inflammatory Th17 and NK cell cytotoxicity may be central. Ongoing subclinical endometrial infection and/or inflammation with increased secretion of TNFα and stimulation of autoimmunity to heat shock proteins may also be contributory. Therapies with a varying theoretical basis and clinical evidence aimed at reducing excessive endometrial immune activity have been used non-selectively in women with RM with variable success. Recent work has now improved our understanding of the role of the different immune cells and proteins that are important at each stage of a normal pregnancy. The vulnerability of the early embryo to T and NK cell-mediated rejection suggests that immune-based therapies need to be maximally effective during early pregnancy. Targeting RM women with demonstrable T and NK cell activity may improve the overall clinical efficacy of these treatments. It may also prevent costly and possibly harmful use in women who are unlikely to respond, and make better use of scarce resources. This report describes the underlying principles behind the use of the different immune-based therapies. The broad evidence supporting their efficacy is also described, as are the possible adverse consequences. Suggestions are also made on how the maternal immune system may be positively modulated using current, widely available treatments that have minimal or no side effects.

Activated T cells Inhibit NK Cell‐mediated Tumour Rejection

Previous studies have described the regulation of some T-cell subsets toward natural killer (NK) cells. Naturally occurring CD4(+)CD25(+) T regulatory cells can inhibit NK cell cytotoxicity, while activated interleukin-2 (IL-2) secreting T cells can stimulate NK cells. However, little is known about the impact of the integrity T-cell population on the final outcome of NK cell cytotoxicity. We thus examined the possible role of activated T cells in affecting NK cell cytotoxicity by mixed lymphocyte co-cultures in vitro and a B16 melanoma tumour model in vivo. In our study, activated T cells were found to be able to significantly inhibit NK cell cytotoxicity in vitro and blunt NK cell-mediated tumour rejection in vivo. The inhibition of NK cell function is a cell-cell contact dependent way. Results suggest that activated T cells may play an important role in limiting NK cell functions, which might be very significant for the design of biotherapy against tumour or infection in future.

Suppression of natural killer cell-mediated bone marrow cell rejection by CD4+CD25+ regulatory T cells.

Naturally occurring CD4(+)CD25(+) T regulatory (Treg) cells have been shown to inhibit adaptive responses by T cells. Natural killer (NK) cells represent an important component of innate immunity in both cancer and infectious disease states. We investigated whether CD4(+)CD25(+) Treg cells could affect NK cell function in vivo by using allogeneic (full H2-disparate) bone marrow (BM) transplantation and the model of hybrid resistance, in which parental marrow grafts are rejected solely by the NK cells of irradiated (BALB/c x C57BL/6) F(1) recipients. We demonstrate that the prior removal of host Treg cells, but not CD8(+) T cells, significantly enhanced NK cell-mediated BM rejection in both models. The inhibitory role of Treg cells on NK cells was confirmed in vivo with adoptive transfer studies in which transferred CD4(+)CD25(+) cells could abrogate NK cell-mediated hybrid resistance. Anti-TGF-beta mAb treatment also increased NK cell-mediated BM graft rejection, suggesting that the NK cell suppression is exerted through TGF-beta. Thus, CD4(+)CD25(+) Treg cells can potently inhibit NK cell function in vivo, and their depletion may have therapeutic ramifications for NK cell function in BM transplantation and cancer therapy.

75 INHIBITION OF NK CELL CYTOTOXICITY IN CLONED MINI-PIGS EXPRESSING HUMAN LEUKOCYTE ANTIGEN-G1 (HLA-G1) GENE

Human natural killer (NK) cell-mediated response plays an important role in xenograft rejection. In the case of pig-to-human xenotransplantation, it has been suggested that NK cells are involved in delayed-type rejection, which is characterized by pig endothelial cell (pEC) activation, direct lysis, and secretion of proinflammatory cytokines. NK cell activation can be a direct barrier to the potential use of pig organs for human xenograft transplantation. Therefore, it is important to suppress the NK cell activity on pig-to-human xenografts. Expression of HLA-G1 (non-classical major histocompatibility complex class I molecules) inhibits the cytotoxic activity of NK cells and has been proposed as a potential solution to overcome NK cell-mediated xenogeneic cytotoxicity in pEC. In this study, we transfected the HLA-G1 gene into mini-pig fetal fibroblasts to produce 2 HLA-G1 clonal cell lines. These cell lines were used to produce cloned HLA-G1 transgenic mini-pigs by nuclear transfer (NT). The presence of the HLA-G1 gene in transgenic mini-pigs was confirmed by PCR. The expression of HLA-G1 was detected by flow cytometry-immunohistochemistry assay. Mini-pig fibroblasts derived from a 35-day-old cloned fetus also showed characteristics similar to those of HLA-G1 clonal cell lines. The expressed HLA-G1 significantly suppressed NK-mediated cell lysis, and the rate of NK 92MI cell cytotoxicity was reduced as compared to the control group (HLA-G1: 46.7 � 4.5%; control: 4.6 � 13.3%; P < 0.05). In conclusion, transgenic cloned mini-pigs expressing HLA-G1 were produced by NT for the first time. It is expected that these mini-pigs could be used to overcome the NK cell-mediated rejection in xenotransplantation.

Natural Killer Cell-Mediated Rejection of Experimental Human Lung Cancer by Genetic Overexpression of Major Histocompatibility Complex Class I Chain-Related Gene A

Natural Killer Cell-Mediated Rejection of Experimental Human Lung Cancer by Genetic Overexpression of Major Histocompatibility Complex Class I Chain-Related Gene A

Natural Killer Cell-Mediated Rejection of Experimental Human Lung Cancer by Genetic Overexpression of Major Histocompatibility Complex Class I Chain-Related Gene A

Studies have highlighted molecular and cell biological mechanisms of the NKG2D-NKG2D ligand system in the activation of natural killer (NK) cell and T cell functions. In this study we explore the potential of genetic overexpression of human major histocompatibility complex class I chain-related gene A (MICA), a powerful NKG2D ligand, for the induction of NK cell-mediated antitumor immunity in a humanized murine model of non-small cell lung cancer. Using tissue microarray technology we detected expression of MICA in only 30% of the samples from patients with lung cancer. Staining was always weak and focal, indicating that expression of MICA is detectable but limited in human lung cancer. Genetic overexpression of MICA by means of adenoviral transduction or transfection of expression plasmids was feasible in cell lines in vitro, primary human cancer tissue ex vivo, and in experimental human cancers in vivo. The presence of MICA on the surface of largely NK cell-resistant human lung cancer cells reestablished NK cell susceptibility and provoked NK cell-mediated antitumor immunity by murine and human NK cells in two different experimental therapy models. In this study we analyze the interaction of human NK cells with MICA-positive human cancer cells in an in vivo setting. Our data demonstrate that MICA overexpression can function as NK cell-mediated immunotherapy in experimental lung cancer.

Suppression of NK Cell-Mediated Bone Marrow Cell Rejection by CD4+CD25+ Regulatory T Cells: Linkage of Adaptive to Innate Responses.

While a link between the innate to adaptive immune system has been established, studies demonstrating direct effects of T cells in regulating Natural Killer (NK) cell function have been lacking. Naturally occurring CD4+CD25+ regulatory T cells (Tregs) have been shown to potently inhibit adaptive responses by T cells. We therefore investigated whether Tregs could affect NK cell function in vivo. Using a bone marrow transplantation (BMT) model of hybrid resistance, in which parental (H2d) marrow grafts are rejected by the NK cells of the F1 recipients (H2bxd), we demonstrate that the in vivo removal of host Tregs significantly enhances NK-cell mediated BM rejection. This heightened rejection was mediated by the specific NK cell Ly-49+ subset previously demonstrated to reject the BMC in this donor/host pairing. The depletion of Tregs could also further increase rejection already enhanced by treating recipients with the NK cell activator, poly I:C. Although splenic NK cell numbers were not significantly altered, increased splenic NK in vitro cytotoxic activity was observed from the recovered cells. The regulatory role of Tregs was confirmed in adoptive transfer studies in which transferred CD4+CD25+ Tregs resulted in abrogation of NK cell-mediated hybrid resistance. Thus, Tregs can potently inhibit NK cell function in vivo and their depletion may have therapeutic ramifications with NK cell function in BMT and cancer therapy.

NKG2D in Tumor and Graft Surveillance

Natural killer (NK) cells are involved in graft rejection and may contribute to tumor recognition and elimination. Ogasawara et al. report that increased production of NKG2D ligands may be one mechanism by which certain tissues are prone to graft rejection and that antibodies against NKGD2 can prevent rejection in these cases. Oppenheim et al. report that localized high expression of NKG2D ligands inhibited NK cell function, contributing to evasion of the immune system by tumors. To study graft rejection, Ogasawara et al. evaluated NKG2D ligand expression (by antibody staining) of bone marrow cells from BALB/C or C57BL/6 mice that were transplanted into irradiated F 1 progeny from a BALB/C C57BL/6 cross, an example of F 1 hybrid resistance. The BALB/C cells expressed the ligand Rae-1 and were rejected by the F1 progeny mice. The C57BL/6 mouse cells were also rejected, but they did not express any NKG2D ligands; thus, there are at least two mechanisms for NK cell-mediated rejection. Depletion of the NK cells from the recipient mice allowed the transplanted cells from both parental strains to survive; however, only in the case of the BALB/C transplanted cells did neutralizing antibodies to NKG2D increase the incorporation of the transplanted cells in the spleens of the recipient mice. The Rae-1 ligand was also the focus of the studies by Oppenheim et al. In this case, two kinds of transgenic mice were generated: those expressing Rae-1ε in squamous epithelium only (lines 110 and 121) and those expressing Rae-1ε ubiquitously (line 187). Both types of transgenic mice showed decreased abundance of NKG2D-positive NK cells; however, the abundance of other proteins (such as CD94) typically expressed by this population of NK cells was normal. Thus, the NKG2D receptor itself appeared to be down-regulated rather than the cell population depleted. Coculturing of NKG2D-positive splenocytes with the splenocytes from the 187 line (high Rae-11ε) resulted in loss of NKG2D from the nontransgenic cells. Injection of a mixture of splenocytes from the 187 line and control splenocytes into control mice or transgenic mice showed that clearance of the Rae-1-positive cells was impaired in the transgenic mice. Activation of the NK cells with poly (I:C) restored killing of the Rae-1-positive cells in the epithelial transgenic mice only, suggesting that a residual population of NKG2D-positive cells could be rescued in the 110 and 121 lines. Finally, the transgenic mice showed increased susceptibility to tumorigenesis (chemical induced and injection of tumor cells). Thus, the NKG2D receptor is a critical player in tumor surveillance and graft rejection. K. Ogasawara, J. Benjamin, R. Takaki, J. H. Phillips, L. L. Lanier, Function of NKG2D in natural killer cell-mediated rejection of mouse bone marrow grafts. Nat. Immunol. 6 , 938-945 (2005). [Online Journal] D. E. Oppenheim, S. J. Roberts, S. L. Clarke, R. Filler, J. M. Lewis, R. E. Tigelaar, M. Girardi, A. C. Hayday, Sustained localized expression of ligand for the activating NKG2D receptor impairs natural cytotoxicity in vivo and reduces tumor surveillance. Nat. Immunol. 6 , 928-937 (2005). [Online Journal]

Blastocyst MHC, a putative murine homologue of HLA-G, protects TAP-deficient tumor cells from natural killer cell-mediated rejection in vivo.

Blastocyst MHC is a recently identified mouse MHC class Ib gene, which is selectively expressed in blastocyst and placenta, and may be the mouse homolog of HLA-G gene the products of which have been implicated in protection of fetal trophoblasts from maternal NK cells and evasion of some tumor cells from NK cell attack. In this study, we identified two blastocyst MHC gene transcripts encoding a full-length alpha-chain (bc1) and an alternatively spliced form lacking the alpha2 domain (bc2), which may be homologous to HLA-G1 and HLA-G2, respectively. Both placenta and a teratocarcinoma cell line predominantly expressed the bc2 transcript. When these cDNAs were expressed in TAP-deficient RMA-S or TAP-sufficient RMA cells, only bc1 protein was expressed on the surface of RMA cells, but both bc1 and bc2 proteins were retained in the cytoplasm of RMA-S cells. Significantly, the RMA-S cells expressing either bc1 or bc2 were protected from lysis by NK cells in vitro. This protection was at least partly mediated by up-regulation of Qa-1(b) expression on the surface of RMA-S cells, which engaged the CD94/NKG2A inhibitory receptor on NK cells. More importantly, the bc1- or bc2-expressing RMA-S cells were significantly protected from NK cell-mediated rejection in vivo. These results suggested a role for blastocyst MHC in protecting TAP-deficient trophoblasts and tumor cells from NK cell attack in vivo.

Ectopic expression of retinoic acid early inducible-1 gene (RAE-1) permits natural killer cell-mediated rejection of a MHC class I-bearing tumor in vivo.

In 1986, Kärre and colleagues reported that natural killer (NK) cells rejected an MHC class I-deficient tumor cell line (RMA-S) but they did not reject the same cell line if it expressed MHC class I (RMA). Based on this observation, they proposed the concept that NK cells provide immune surveillance for "missing self," e.g., they eliminate cells that have lost class I MHC antigens. This seminal observation predicted the existence of inhibitory NK cell receptors for MHC class I. Here, we present evidence that NK cells are able to reject tumors expressing MHC class I if the tumor expresses a ligand for NKG2D. Mock-transfected RMA cells resulted in tumor formation. In contrast, when RMA cells were transfected with the retinoic acid early inducible gene-1 gamma or delta (RAE-1), ligands for the activating receptor NKG2D, the tumors were rejected. The tumor rejection was mediated by NK cells, and not by CD1-restricted NK1.1(+) T cells. No T cell-mediated immunological memory against the parental tumor was generated in the animals that had rejected the RAE-1 transfected tumors, which succumbed to rechallenge with the parental RMA tumor. Therefore, NK cells are able to reject a tumor expressing RAE-1 molecules, despite expression of self MHC class I on the tumor, demonstrating the potential for NK cells to participate in immunity against class I-bearing malignancies.

Transgenic expression of the Ly49A natural killer cell receptor confers class I major histocompatibility complex (MHC)-specific inhibition and prevents bone marrow allograft rejection.

Natural killer (NK) cells and some T cells are endowed with receptors specific for class I major histocompatibility complex (MHC) molecules that can inhibit cellular effector functions. The function of the Ly49 receptor family has been studied in vitro, but no gene transfer experiments have directly established the role of these receptors in NK cell functions. We show here that transgenic expression of the H-2Dd-specific Ly49A receptor in all NK cells and T cells conferred class I-specific inhibition of NK cell-mediated target cell lysis as well as of T cell proliferation. Furthermore, transgene expression prevented NK cell-mediated rejection of allogeneic H-2d bone marrow grafts by irradiated mice. These results demonstrate the function and specificity of Ly49 receptors in vivo, and establish that their subset-specific expression is necessary for the discrimination of MHC-different cells by NK cells in unmanipulated mice.

Acute rejection of marrow grafts in mice. Dependence on and independence of functional TCR in the rejection process.

The question of how irradiated mice acutely reject marrow grafts has remained controversial, and evidence in support of T cell- and natural killer cell-mediated rejection mechanisms has been provided. Here we show in support of previous data that CB17 severe combined immunodeficiency mice acutely reject allogeneic marrow but the specificity of rejection cannot be mapped within the MHC. It is shown that a similar rejection specificity is also expressed in normal CB17 mice and that it is caused by CD3- or CD3+ effector cells that do not utilize TCR. In search of TCR-independent rejection mechanisms in other mouse strains, use is made of TCR transgenic mice expressing a defect in recognizing H-2Dd. It is shown that, although marrow graft rejection is impaired in these mice, pointing to participation of TCR in the rejection process, residual resistance does exist. This resistance maps to the MHC, cannot be shown to involve TCR, and appears to be expressed by NK1+ CD3+ cells. It is concluded that acute marrow graft rejection in normal mice can be mediated by both TCR-mediated and NK cell receptor-dependent effector mechanisms, depending on the particular mouse strains.