The innate immune response to tumors and its role in the induction of T-cell immunity

Natural killer cells and cancer: regulation by the killer cell Ig-like receptors (KIR)

Natural killer (NK) cells are innate immune effector cells that make up approximately 10-15% of the peripheral blood lymphocytes in humans and are primarily involved in immunosurveillance to eliminate transformed and virally-infected cells. They were originally defined by their ability to spontaneously eliminate rare cells lacking expression of class I major histocompatibility complex (MHC-I) self molecules, which is commonly referred to as "missing self" recognition. The molecular basis for missing self recognition emerges from the expression of MHC-I-specific inhibitory receptors on the NK cell surface that tolerize NK cells toward normal MHC-I-expressing cells. By lacking inhibitory receptor ligands, tumor cells or virus-infected cells that have down-modulated surface MHC-I expression become susceptible to attack by NK cells. Killer cell Ig-like receptors (KIR; CD158) constitute a family of MHC-I binding receptors that plays a major role in regulating the activation thresholds of NK cells and some T cells in humans. Here, we review the multiple levels of KIR diversity that contribute to the generation of a highly varied NK cell repertoire and explain how this diversity can influence susceptibility to a variety of diseases, including cancer. We further describe strategies by which KIR can be manipulated therapeutically to treat cancer, through the exploitation of KIR/MHC-I ligand mismatch to potentiate hematopoietic stem cell transplantation and the use of KIR blockade to enhance tumor cell killing.

Immunotherapy for neuroblastoma: turning promise into reality

Neuroblastoma is one of the commonest and most aggressive paediatric malignancies. The majority of children present with metastatic disease for which long-term survival remains poor despite intensive multi-modal therapies. Toxicity from current treatment regimes is already significant, and there is little room to further intensify therapy. Alternative treatment strategies are therefore needed in order to improve survival. Immunotherapy is an attractive therapeutic option for these children as it potentially offers a much more specific and less toxic treatment than conventional therapies. This review discusses the different immunotherapy strategies that may be useful in neuroblastoma, their advantages and disadvantages and the challenges that need to be overcome to successfully use them clinically.

Cancer immunotherapy

Recent scientific advances have expanded our understanding of the immune system and its response to malignant cells. The clinical goal of tumour immunotherapy is to provide either passive or active immunity against malignancies by harnessing the immune system to target tumours. Monoclonal antibodies, cytokines, cellular immunotherapy, and vaccines have increasingly become successful therapeutic agents for the treatment of solid and haematological cancers in preclinical models, clinical trials, and practice. In this article, we review recent advances in the immunotherapy of cancer, focusing on new strategies and future perspectives as well as on clinical trials attempting to enhance the efficacy of immunotherapeutic modalities and translate this knowledge into effective cancer therapies.

A high proportion of bone marrow T cells with regulatory phenotype (CD4+CD25hiFoxP3+) in Ewing sarcoma patients is associated with metastatic disease

Immunosuppressive CD4+CD25(hi)FoxP3+ T cells (T(reg) cells) have been found at increased densities within the tumor microenvironment in many malignancies and interfere with protective antitumor immune responses. Osseous Ewing sarcomas (ESs) are thought to derive from a bone marrow (BM) mesenchymal cell of origin, and microscopic marrow involvement defines a subpopulation of patients at a high risk of relapse. We hypothesized that BM-resident T cells may contribute to a permissive milieu for immune escape of ESs. Using 6-color-flow cytometry, we investigated the pattern of immune cell subset distribution including NK cells, gammadelta T cells, central and effector memory CD8+ and CD4+ T cells as well as T cells with regulatory phenotype (T(reg) cells) in BM obtained at diagnosis from 45 primary or relapsed ES patients treated within standardized protocols. Although patients at relapse had an inverted CD4:CD8 T-cell ratio, neither CD8+ effector/memory T-cell subsets nor T(reg) cells significantly differed from patients at diagnosis. No significant associations of innate and effector/memory T-cell subpopulations with known risk factors were found, including age, gender, tumor site, primary metastases and histological tumor response. By contrast, T(reg) cells were found at significantly higher frequencies in patients with primary metastatic disease compared with localized ESs (5.0 vs. 3.3%, p = 0.01). Thus, increased BM T(reg) cells in patients with metastasized ES may reflect an immune escape mechanism that contributes to the development of metastatic disease. Immunotherapeutic strategies will have to adequately consider the regulatory milieu within areas of Ewing tumor-immune interactions.

Obstructing shedding of the immunostimulatory MHC class I chain-related gene B prevents tumor formation

PURPOSE

Clinical observations have suggested that shedding of the MHC class I chain-related molecule (MIC) may be one of the mechanisms by which tumors evade host immunosurveillance and progress. However, this hypothesis has never been proven. In this study, we tested this hypothesis using a prostate tumor model and investigated the effect of shedding of MIC on tumor development.

EXPERIMENTAL DESIGN

We generated a shedding-resistant noncleavable form of MICB (MICB.A2). We overexpressed MICB.A2, the wild-type MICB, and the recombinant soluble MICB (rsMICB) in mouse prostate tumor TRAMP-C2 (TC2) cells and implanted these cells into severe combined immunodeficient mice.

RESULTS

No tumors were developed in animals that were implanted with TC2-MICB.A2 cells, whereas all the animals that were implanted with TC2, TC2-MICB, or TC2-rsMICB cells developed tumors. When a NKG2D-specific antibody CX5 or purified rsMICB was administered to animals before tumor implantation, all animals that were implanted with TC2-MICB.A2 cells developed tumors. In vitro cytotoxicity assay revealed the loss of NKG2D-mediated natural killer cell function in these prechallenged animals, suggesting that persistent levels of soluble MICB in the serum can impair natural killer cell function and thus allow tumor growth.

CONCLUSIONS

These data suggest that MIC shedding may contribute significantly to tumor formation by transformed cells and that inhibition of MIC shedding to sustain the NKG2D receptor-MIC ligand recognition may have potential clinical implication in targeted cancer treatment.

Killer cell immunoglobulin-like receptor gene polymorphisms in patients with leukemia: possible association with susceptibility to the disease

Accumulating evidences suggest that killer cell immunoglobulin-like receptors (KIRs) contribute to the pathogenesis of diverse kinds of diseases. However, the functions and effects of KIR gene polymorphisms in the development of diseases remain largely unknown, especially about the activating KIR genes. To investigate the association of KIR gene polymorphisms with subtypes of leukemia, we carried out the present study on 263 patients with leukemia and 239 healthy controls by means of polymerase chain reaction-sequence-specific primer and analysis, and then all data were analyzed by Logistic regression method. Our results showed that the frame genotypes of KIR2DL4, 3DL2, 3DL3 and 3DP1 were expressed in all patients and all controls. The genotypes of KIR2DL1, 2DL3, 3DL1, and 2DP1 were most prevalent genotypes whose rates were more than 95% in all patients and all controls. The rate of activating KIR2DS4 was much higher in patients with CML than that in healthy controls (P<0.001) while the activating KIR2DS3 was lower in patients with ALL compared with healthy controls (P<0.05). There was no significant change of KIR genes found in patients with NALL. In conclusion, this study suggests that the activating KIR2DS4 may serve as CML susceptive gene to trigger leukemia development, while KIR2DS3 is possibly a protect gene of ALL.

Evolution and survival of marine carnivores did not require a diversity of killer cell Ig-like receptors or Ly49 NK cell receptors

Ly49 lectin-like receptors and killer cell Ig-like receptors (KIR) are structurally unrelated cell surface glycoproteins that evolved independently to function as diverse NK cell receptors for MHC class I molecules. Comparison of primates and various domesticated animals has shown that species have either a diverse Ly49 or KIR gene family, but not both. In four pinniped species of wild marine carnivore, three seals and one sea lion, we find that Ly49 and KIR are each represented by single, orthologous genes that exhibit little polymorphism and are transcribed to express cell surface protein. Pinnipeds are therefore species in which neither Ly49 nor KIR are polygenic, but retain the ancestral single-copy state. Whereas pinniped Ly49 has been subject to purifying selection, we find evidence for positive selection on KIR3DL during pinniped evolution. This selection, which focused on the D0 domain and the stem, points to the functionality of the KIR and most likely led to the sea lion's loss of D0. In contrast to the dynamic and rapid evolution of the KIR and Ly49 genes in other species, the pinniped KIR and Ly49 have been remarkably stable during the >33 million years since the last common ancestor of seals and sea lions. These results demonstrate that long-term survival of placental mammal species need not require a diverse system of either Ly49 or KIR NK cell receptors.

Tumor vaccines for breast cancer

The goal of cancer vaccines and immunotherapies is to train the immune system to recognize cancer cells and destroy them. Immune responses play a dynamic role in the development of cancers, from immunosurveillance to immune escape; from in situ immune dysregulation to metastatic spread. The systematic identification and targeting of molecules involved in the immune response has led to a wide variety of potential immunotherapeutic targets for the treatment of breast cancer. Extraordinary advances in molecular immunology have led to a detailed understanding of tumor antigens, antigen presentation, innate immunity, cytokine and chemokine pathways, and immunoregulation. Many of these vaccine therapies are already in clinical development. It is the rational and rapid translation of these scientific discoveries into effective therapies for patients with breast cancer that poses the greatest challenge, and opportunity, to realize the potential of tumor vaccine therapy for breast cancer.

NK-cell-mediated killing of target cells triggers robust antigen-specific T-cell-mediated and humoral responses

Previous work showed that administration of antigen-expressing apoptotic cells in vivo results in antigen-specific CD8+ T-cell responses independent of Toll-like receptor signaling. We report here that natural killer (NK) cells can serve a function directly upstream of this pathway and initiate robust adaptive immune responses via killing of antigen-expressing target cells. This pathway is highly sensitive, in that administration of as few as 10(4) target cells induced detectable antigen-specific CD8+ T-cell responses. Importantly, NK cell-mediated cytotoxicity of target cells could also induce robust antigen-specific CD4+ T-cell responses, which were critical for subsequent CD8+ T-cell priming and IgG responses. Unlike adaptive immune responses induced by gamma-irradiated cells, the NK-cell pathway required myeloid differentiating factor 88 (MyD88) and Toll/interleukin-1 receptor domain-containing adapter-inducing interferon-beta (Trif) signaling. NK cells have previously been shown to detect and kill pathogen-infected host cells, as well as neoplastic cells and tissue allografts. The present data provide further evidence that they also discharge a strong tie with their relatives in the adaptive immune system. We think that the recognition and killing of target cells by NK cells represents an important pathway for the generation of robust CD8+ T and humoral responses that may be exploited for vaccine development.

NK cell responsiveness is tuned commensurate with the number of inhibitory receptors for self-MHC class I: the rheostat model

Inhibitory receptors that engage self-MHC class I molecules enable NK cells to detect disease-associated loss of MHC class I on surrounding cells. Previous studies showed that some NK cells lack all receptors for self-MHC class I, yet fail to exhibit autoimmunity because they are generally hyporesponsive to stimulation. We asked whether NK cells exist in only two states, responsive and hyporesponsive, corresponding to cells that express or fail to express inhibitory receptors for self-MHC class I. The alternative model is that NK cells vary continuously in their responsiveness, based on variations in the number of different inhibitory and stimulatory receptors they express, which is known to vary. In this study, we show in the murine system that NK cell responsiveness increases quantitatively with each added self-MHC-specific inhibitory receptor. Genetic analysis demonstrated that interactions of each of the receptors with self-MHC class I were necessary to observe augmented responsiveness. These findings suggest that NK cell responsiveness is comparable to a rheostat: it is tuned to an optimal set point depending on the inhibitory and stimulatory interactions encountered in the normal environment, so as to ensure self-tolerance and yet optimize sensitivity to changes in normal cells.

Mutual activation of CD4+ T cells and monocytes mediated by NKG2D-MIC interaction requires IFN-gamma production in systemic lupus erythematosus

The activating receptor NKG2D is mainly expressed by human CD8(+) T cells and NK cells but normally absent on CD4(+) T cells. However, a subset of autoreactive NKG2D(+)CD4(+) T cells has been found to exist in some autoimmune disease such as rheumatoid arthritis (RA) and to participate in the imbalance of immune response and inflammation. Up to date this observation has been extended to some autoimmune diseases such as RA and Crohn's disease and the mechanism underlying the presence of this type of NKG2D(+)CD4(+) T cells has not been delineated yet. In this study, we found that a substantial proportion of CD4(+) T cells expressed NKG2D in the PBMC of SLE patients. We also found that monocytes in SLE aberrantly expressed the NKG2D ligand of MHC class I chain-related (MIC) molecules and membrane-bound IL-15 (mIL-15) at the cell surface. When cultured with the sera from SLE patients, the monocytes from healthy volunteers could be induced to express MIC and mIL-15. However, this induced expression of MIC and mIL-15 could be blocked with anti-IFN-gamma receptor (anti-IFN-gammaR) antibody. We further demonstrated that NKG2D could be induced on normal CD4(+) T cells either cocultured with monocytes from patients with SLE, or monocytes from healthy volunteers but pretreated with IFN-gamma. Moreover, Th1 cytokines were found to be produced by NKG2D(+)CD4(+) T cells in the coculture system. By transwell assay, we found that both NKG2D expression and Th1 cytokines production depended on the cell-cell contact. These results indicate that the elevated sera IFN-gamma may be responsible for MIC and mIL-15 induction on monocytes in SLE; mIL-15 on monocytes contribute to NKG2D receptor induction on a subset of CD4(+) T cells. Moreover, CD14(+) monocytes promote NKG2D(+)CD4(+) T cells activation through the NKG2D-MIC engagement in the pathogenesis of SLE.

Protein disulfide isomerases are antibody targets during immune-mediated tumor destruction

The identification of cancer antigens that contribute to transformation and are linked with immune-mediated tumor destruction is an important goal for immunotherapy. Toward this end, we screened a murine renal cell carcinoma cDNA expression library with sera from mice vaccinated with irradiated tumor cells engineered to secrete granulocyte macrophage colony-stimulating factor (GM-CSF). Multiple nonmutated, overexpressed proteins that function in tumor cell migration, protein/nucleic acid homeostasis, metabolism, and stress responses were detected. Among these, the most frequently recognized clone was protein disulfide isomerase (PDI). High titer antibodies to human PDI were similarly induced in an acute myeloid leukemia patient who achieved a complete response after vaccination with irradiated, autologous GM-CSF-secreting tumor cells in the setting of nonmyeloablative allogeneic bone marrow transplantation. Moreover, ERp5, a closely related disulfide isomerase involved in major histocompatibility complex (MHC) class I chain-related protein A (MICA) shedding, also evoked potent humoral reactions in diverse solid and hematologic malignancy patients who responded to GM-CSF-secreting tumor cell vaccines or antibody blockade of cytotoxic T lymphocyte-associated antigen 4 (CTLA-4). Together, these findings reveal the unexpected immunogenicity of PDIs and raise the possibility that these gene products might serve as targets for therapeutic monoclonal antibodies.

TLRs and innate immunity

One of the most fundamental questions in immunology pertains to the recognition of non-self, which for the most part means microbes. How do we initially realize that we have been inoculated with microbes, and how is the immune response ignited? Genetic studies have made important inroads into this question during the past decade, and we now know that in mammals, a relatively small number of receptors operate to detect signature molecules that herald infection. One or more of these signature molecules are displayed by almost all microbes. These receptors and the signals they initiate have been studied in depth by random germline mutagenesis and positional cloning (forward genetics). Herein is a concise description of what has been learned about the Toll-like receptors, which play an essential part in the perception of microbes and shape the complex host responses that occur during infection.

Serum soluble interleukin 2 receptor alpha in human cancer of adults and children: a review

Cancer growth and development is associated with the stimulation of the innate immune system, including enhanced interleukin 2 receptor (IL-2R) expression in immune cells and its shedding into the circulation in a soluble form of sIL-2Ralpha. In most haematological malignancies, including different types of leukaemias and lymphomas, sIL-2Ralpha has been found to be released directly from the surface of neoplastic cells thus reflecting the tumour bulk, turnover and activity. Several studies have proved that not only lymphoid cancer cells, but also some non-lymphoid cancer cells, express IL-2R on their surface. They include malignant melanoma and carcinomas of the kidney, head and neck, oesophagus and lung. It is suggested that in most malignant solid tumours, elevated levels of sIL-2Ralpha are likely to be the product of normal peripheral mononuclear cells activated in response to the neoplasm's growth or that they are released from activated lymphoid cells infiltrating neoplastic tissues. This latter hypothesis has been proved by discovering the high expression of CD25 on the cell surface of most of these cells. Although the precise source and biological role of sIL-2Ralpha has not been clarified definitively, pretreatment serum levels of sIL-2Ralpha have been shown to reflect the activity, advancement and biological aggressiveness of many types of cancer in adults and children as well as to correlate with prognosis and overall survival. The possibility of enriching the diagnostic tools of oncologists with a new biochemical marker of activity of neoplasms resulted in numerous studies and reports concerning the clinical usefulness of sIL-2Ralpha measurements in adult and, less frequently, in paediatric malignancies. This article presents the actual knowledge concerning the structure, source and biological function of sIL-2Ralpha in patients with haematological and non-haematological malignancies. The authors review the published data on clinical applicability of soluble IL-2Ralpha determination in terms of diagnostics, prognosis and treatment monitoring of particular types of malignant disorders both in adults and in children. They also provide an insight into the clinical usefulness of sLL-2Ralpha-blocking antibodies in patients with cancer, and in those who reject organ transplants, develop graft-versus-host disease after allogeneic bone marrow transplantation and are affected with autoimmune disorders.

Leukocyte numbers and function in subjects eating n-3 enriched foods: selective depression of natural killer cell levels

Introduction

While consumption of omega-3 long-chain polyunsaturated fatty acids (n-3 LCPUFA) has been recommended for those at risk of inflammatory disease such as rheumatoid arthritis, the mechanism of their anti-inflammatory effect remains to be clearly defined, particularly in relation to the dose and type of n-3 LCPUFA. The objective of this study was to determine whether varying the levels of n-3 LCPUFA in erythrocyte membrane lipids, following dietary supplementation, is associated with altered numbers and function of circulating leukocytes conducive to protection against inflammation.

Methods

In a double-blind and placebo-controlled study, 44 healthy subjects aged 23 to 63 years consumed either standard or n-3 LCPUFA-enriched versions of typical processed foods, the latter allowing a target daily consumption of 1 gram n-3 LCPUFA. After six months, peripheral blood leukocyte and subpopulation proportions and numbers were assessed by flow cytometry. Leukocytes were also examined for lymphoproliferation and cytokine production, neutrophil chemotaxis, chemokinesis, bactericidal, adherence and iodination activity. Erythrocytes were analyzed for fatty-acid content.

Results

Erythrocyte n-3 LCPUFA levels were higher and absolute leukocyte and lymphocyte numbers were lower in subjects consuming n-3 enriched foods than in controls. There were no changes in the number of neutrophils, monocytes, T cells (CD3⁺), T-cell subsets (CD4⁺, CD8⁺) and B cells (CD19⁺). However, natural killer (NK) (CD3^-CD16⁺CD56⁺) cell numbers were lower in n-3 supplemented subjects than in controls and were inversely related to the amount of eicosapentaenoic acid or docosahexaenoic acid in erythrocytes. No significant correlations were found with respect to lymphocyte lymphoproliferation and production of IFN-γ and IL-2, but lymphotoxin production was higher with greater n-3 LCPUFA membrane content. Similarly, neutrophil chemotaxis, chemokinesis, bactericidal activity and adherence did not vary with changes in erythrocyte n-3 LCPUFA levels, but the iodination reaction was reduced with higher n-3 LCPUFA content.

Conclusion

The data show that regular long-term consumption of n-3 enriched foods leads to lower numbers of NK cells and neutrophil iodination activity but higher lymphotoxin production by lymphocytes. These changes are consistent with decreased inflammatory reaction and tissue damage seen in patients with inflammatory disorders receiving n-3 LCPUFA supplementation.

Combination of KIR and HLA gene variants augments the risk of developing birdshot chorioretinopathy in HLA-A*29-positive individuals

Birdshot chorioretinopathy (BCR), a chronic ocular inflammatory disease with characteristic choroidal lymphocytic infiltrates, has been strongly associated with human leukocyte antigen (HLA)-A29. Although HLA-A29 occurs frequently in all populations, BCR affects only a small percentage of HLA-A29-positive Caucasians, indicating additional susceptibility factors for BCR. Discovery of HLA class I-specific killer cell immunoglobulin-like receptors (KIR) led to a series of epidemiological studies implicating KIR-HLA gene combinations in disease. Here, we characterized KIR-HLA pairs in BCR patients and controls carrying HLA-A*29 as well as controls lacking HLA-A*29. KIR-HLA pairs implicated for weak inhibition (KIR2DL2/3+HLA-C1 and KIR3DL1+HLA-Bw4(T80)) in combination with activating KIR genes associated with autoimmunity (KIR2DS2, 2DS3 and 2DS4) augment the risk of developing BCR in HLA-A*29-positive individuals. The reciprocal association of strong inhibitory pairs (KIR3DL1+HLA-Bw4(I80) and KIR2DL1+HLA-C2) in combination with those implicated in protection from infection (KIR3DS1+HLA-Bw4(I80) and KIR2DS1+HLA-C2) was observed in HLA-A*29-negative controls. These results suggest that a profound effect of KIR2DS2/S3/S4 in the absence of strong inhibition may enhance the activation of natural killer cells and T-cell subsets against intraocular self-antigens, thereby contributing to pathogenesis of BCR.

MHC class I chain-related protein A antibodies and shedding are associated with the progression of multiple myeloma

Monoclonal gammopathy of undetermined significance (MGUS) is a common disorder of aging and a precursor lesion to full-blown multiple myeloma (MM). The mechanisms underlying the progression from MGUS to MM are incompletely understood but include the suppression of innate and adaptive antitumor immunity. Here, we demonstrate that NKG2D, an activating receptor on natural killer (NK) cells, CD8(+) T lymphocytes, and MHC class I chain-related protein A (MICA), an NKG2D ligand induced in malignant plasma cells through DNA damage, contribute to the pathogenesis of MGUS and MM. MICA expression is increased on plasma cells from MGUS patients compared with normal donors, whereas MM patients display intermediate MICA levels and a high expression of ERp5, a protein disulfide isomerase linked to MICA shedding (sMICA). MM, but not MGUS, patients harbor circulating sMICA, which triggers the down-regulation of NKG2D and impaired lymphocyte cytotoxicity. In contrast, MGUS, but not MM, patients generate high-titer anti-MICA antibodies that antagonize the suppressive effects of sMICA and stimulate dendritic cell cross-presentation of malignant plasma cells. Bortezomib, a proteasome inhibitor with anti-MM clinical efficacy, activates the DNA damage response to augment MICA expression in some MM cells, thereby enhancing their opsonization by anti-MICA antibodies. Together, these findings reveal that the alterations in the NKG2D pathway are associated with the progression from MGUS to MM and raise the possibility that anti-MICA monoclonal antibodies might prove therapeutic for these disorders.

Increased glioma growth in mice depleted of macrophages

Macrophages can promote the growth of some tumors, such as those of the breast and lung, but it is unknown whether this is true for all tumors, including those of the nervous system. On the contrary, we have previously shown that macrophages can slow the progression of malignant gliomas through a tumor necrosis factor-dependent mechanism. Here, we provide evidence suggesting that this antitumor effect could be mediated by T lymphocytes, as their number was drastically reduced in tumor necrosis factor-deficient mice and inversely correlated with glioma volume. However, this correlation was only observed in allogeneic recipients, prompting a reevaluation of the role of macrophages in a nonimmunogenic context. Using syngeneic mice expressing the herpes simplex virus thymidine kinase under the control of the CD11b promoter, we show that macrophages can exert an antitumor effect without the help of T lymphocytes. Macrophage depletion achieved by ganciclovir treatment resulted in a 33% increase in glioma volume. The antitumor effect of macrophages was not likely due to a tumoricidal activity because phagocytosis or apoptosis of glioma cells, transduced ex vivo with a lentiviral vector expressing green fluorescent protein, was rarely observed. Their antitumor effect was also not due to a destructive action on the tumor vasculature because macrophage depletion resulted in a modest reduction in vascular density. Therefore, this study suggests that macrophages can attenuate glioma growth by an unconventional mechanism. This study also validates a new transgenic model to explore the role of macrophages in cancer.

MHC class I chain-related molecules induced on monocytes by IFN-gamma promote NK cell activation

NKG2D receptor-ligand interaction triggers NK cell-mediated cytolysis and IFN-gamma secretion. IFN-gamma produced by NK cells has been found to promote the interaction between NK cells and monocytes; however, the underlying mechanism remains elusive. We demonstrate here that IFN-gamma exclusively induced or upregulated the expression of MHC class I chain-related (MIC) molecules, which are ligands of the NKG2D receptor, on the surface of human monocytes of the PBMC population. The IFN-gamma-induced MIC molecules on monocytes played an essential role in triggering the activation of NK cells because mAb-mediated masking of the MIC molecules and the inhibition of cell-to-cell contact using transwell inserts significantly abolished NK cell activation. Meanwhile, membrane-bound IL-15 (mIL-15) was concomitantly induced with MIC molecules on IFN-gamma-treated monocytes and played an essential role in protecting NK cells cocultured with monocytes from MIC-induced NKG2D down-modulation. Therefore, we conclude that the IFN-gamma-induced MIC molecules participated in monocyte/NK cell interaction and that this interaction also involved mIL-15.

The combined actions of NK and T lymphocytes are necessary to reject an EGFP+ mesenchymal tumor through mechanisms dependent on NKG2D and IFN gamma

Better understanding of the mechanisms that mediate spontaneous immune rejections ought to be important in the quest for improvements in immunotherapy of cancer. A set of intraperitoneal tumors of mesenchymal origin that had been chemically induced in ubiquitously expressing EGFP transgenic mice provided a model in which both T and NK cells were absolutely required for tumor rejection. Tumor cells were traceable because of being fluorescent and readily grafted in RAG1(-/-) immunodeficient mice, whereas they were rejected in a majority of syngeneic C57BL/6 and EGFP-transgenic mice. Tumor-cell clones with the highest EGFP expression tended to be rejected, but a direct involvement of EGFP as the antigen recognized for the immune rejections was ruled out. Rejections were absolutely dependent on NK cells as well as on CD4(+) and CD8(+) T lymphocytes according to selective depletion studies. Furthermore, CD8(+) and CD4(+) T lymphocytes as well as NK cells were detected in the inflammatory infiltrate that mediates tumor rejection along with some DC. The effects of IFN gamma, produced at the tumor site by T and NK lymphocytes, were only required at the malignant cell level and were necessary for tumor eradication. NK recognition of tumor cells was mediated by the NKG2D-activating receptor and blocking its function in vivo partially interfered with rejection. Therefore, complete rejection of these mesenchymal tumors requires a concerted set of activities including direct tumor-cell destruction and IFN gamma production that are mediated by both NK and T cells.

CD69 on CD56+ NK cells and response to chemoimmunotherapy in metastatic melanoma

BACKGROUND

The few chemoimmunotherapy trials that together with dacarbazine (DTIC) and interferon-alpha 2a (IFNalpha), include retinoic acid (RA), did not include detailed immunological evaluation of functional and phenotypic natural killer (NK) cell characteristics, and have shown contradictory clinical results.

MATERIALS AND METHODS

Malignant melanoma (MM) patients undergoing phase II-randomized chemoimmunotherapy trials were treated with DTIC, IFNalpha (Hoffmann-La Roche) (group A, n = 31), and with DTIC, IFNalpha and 13-cis-RA (Isotretinoin, Hoffmann-La Roche, Basel, Switzerland) (group B, n = 29). Patients and 42 healthy controls were evaluated by FACS flow analyses for CD3/CD56/CD69 positive cells, NK cytotoxicity in fresh peripheral blood lymphocytes (PBL) and for interferon regulatory factor-1 mRNA expression by reverse transcriptase polymerase chain reaction in treated PBL.

RESULTS

The addition of RA to a DTIC-IFN regime did not bring any therapeutical benefit in terms of response or survival. Immunological follow-up on days 1, 6 and 27 of each therapy cycle shows a significant increase in NK cell activity in both groups, only on day 6 of the first cycle, while CD69+CD56+ expression increased significantly on day 6 of each therapy cycle, in both groups. Evaluation of the dynamics of expression of IRF-1 of in vitro treated PBL, shows its strong and prompt up-regulation by IFNalpha and synergistic effect of IFNalpha and RA combination.

CONCLUSION

The dynamics of the increase in CD69 early activation antigen expression on CD56+ NK cells is systematic and serial with the increase being significantly higher on day six of the first cycle in group B patients with clinical response, compared to those without, indicating possible predictive value of CD69 expression for clinical response to chemoimmunotherapy.

Chain-terminating natural mutations affect the function of activating KIR receptors 3DS1 and 2DS3

To determine the nucleotide polymorphism of activating killer-cell immunoglobulin-like receptors (aKIR) 3DS1 and 2DS3, we developed a novel direct-sequencing method and analyzed DNA samples of 175 KIR3DS1(+) individuals and 72 KIR2DS3(+) individuals from the white population. The putative ligand-binding extracellular immunoglobulin (Ig)-like domains of these aKIR receptors are highly conserved, a scenario contrary to inhibitory KIRs that recognize polymorphic human leukocyte antigen (HLA) class I molecules. Null alleles 3DS1*049N and 2DS3*003N that do not express cell-surface receptors were discovered, and they occur commonly in whites (3DS1*049N = 2%; 2DS3*003N = 0.8%). Sequence-specific polymerase chain reaction (PCR) detecting these null alleles is negative with DNA from nonwhite subjects, suggesting that these null alleles are specific to whites and probably originated after the colonization of modern humans in Europe.

Genome wide transcriptional analysis of resting and IL2 activated human natural killer cells: gene expression signatures indicative of novel molecular signaling pathways

BACKGROUND

Human natural killer (NK) cells are the key contributors of innate immune response and the effector functions of these cells are enhanced by cytokines such as interleukine 2 (IL2). We utilized genome-wide transcriptional profiling to identify gene expression signatures and pathways in resting and IL2 activated NK cell isolated from peripheral blood of healthy donors.

RESULTS

Gene expression profiling of resting NK cells showed high expression of a number of cytotoxic factors, cytokines, chemokines and inhibitory and activating surface NK receptors. Resting NK cells expressed many genes associated with cellular quiescence and also appeared to have an active TGFbeta (TGFB1) signaling pathway. IL2 stimulation induced rapid downregulation of quiescence associated genes and upregulation of genes associated with cell cycle progression and proliferation. Numerous genes that may enhance immune function and responsiveness including activating receptors (DNAM1, KLRC1 and KLRC3), death receptor ligand (TNFSF6 (FASL) and TRAIL), chemokine receptors (CX3CR1, CCR5 and CCR7), interleukin receptors (IL2RG, IL18RAB and IL27RA) and members of secretory pathways (DEGS1, FKBP11, SSR3, SEC61G and SLC3A2) were upregulated. The expression profile suggested PI3K/AKT activation and NF-kappaB activation through multiple pathways (TLR/IL1R, TNF receptor induced and TCR-like possibly involving BCL10). Activation of NFAT signaling was supported by increased expression of many pathway members and downstream target genes. The transcription factor GATA3 was expressed in resting cells while T-BET was upregulated on activation concurrent with the change in cytokine expression profile. The importance of NK cells in innate immune response was also reflected by late increased expression of inflammatory chemotactic factors and receptors and molecules involved in adhesion and lymphocyte trafficking or migration.

CONCLUSION

This analysis allowed us to identify genes implicated in cellular quiescence and the cytokines and cytotoxic factors ready for immediate immune response. It also allowed us to observe the sequential immunostimulatory effects of IL2 on NK cells improving our understanding of the biology and molecular mediators behind NK cell activation.

The host inflammatory response promotes liver metastasis by increasing tumor cell arrest and extravasation

Inflammation can play a regulatory role in cancer progression and metastasis. Previously, we have shown that metastatic tumor cells entering the liver trigger a proinflammatory response involving Kupffer cell-mediated release of tumor necrosis factor-alpha and the up-regulation of vascular endothelial cell adhesion receptors, such as E-selectin. Here, we analyzed spatio-temporal aspects of the ensuing tumor-endothelial cell interaction using human colorectal carcinoma CX-1 and murine carcinoma H-59 cells and a combination of immunohistochemistry, confocal microscopy, and three-dimensional reconstruction. E-selectin expression was evident mainly on sinusoidal vessels by 6 and 10 hours, respectively, following H-59 and CX-1 inoculation, and this corresponded to a stabilization of the number of tumor cells within the sinuses. Tumor cells arrested in E-selectin(+) vessels and appeared to flatten and traverse the vessel lining, away from sites of intense E-selectin staining. This process was evident by 8 (H-59) and 12 (CX-1) hours after inoculation, coincided with increased endothelial vascular cell adhesion molecule-1 expression, and involved tumor cell attachment in areas of intense vascular cell adhesion molecule-1 and platelet endothelial cell adhesion molecule-1 expression. Nonmetastatic (human) MIP-101 and (murine) M-27 cells induced a weaker response and could not be seen to extravasate. The results show that metastatic tumor cells can alter the hepatic microvasculature and use newly expressed endothelial cell receptors to arrest and extravasate.

Different mechanisms can lead to the same altered HLA class I phenotype in tumors

Human leukocyte antigen (HLA) class I plays an important role in tumor recognition and rejection. Total or selective losses of HLA class I antigens (classified into seven HLA class I altered phenotypes) represent one of the main routes of tumor escape from immune surveillance. Abnormal expression of HLA class I has been reported in different human tumor samples with distinct underlying mechanisms. Notably, different molecular mechanisms can generate the same altered HLA class I phenotype. Here, we describe various molecular mechanisms that can lead to HLA total loss or downregulation (phenotype I) in melanoma, colorectal carcinoma and bladder cancer.

Natural killer cell crossmatch: Functional analysis of inhibitory killer immunoglobulin-like receptors and their HLA ligands

Attempts to predict outcome of bone marrow transplantation based on killer immunoglobulin-like receptor (KIR) and HLA genotyping have yielded discordant results. To better understand the factors involved, we investigated natural killer (NK) cell function and correlated it with genetics and expression of inhibitory KIR and HLA ligands in 20 normal allogeneic pairs. KIR expression was analyzed by flow cytometry to estimate the percentage of NK cells that could be inhibited by the HLA ligands in each pair combination. NK cytotoxicity against ConA blasts demonstrated a positive correlation between the number of KIR/HLA matches and the predicted number of NK cells that could be inhibited. When 50% or more of the NK cells could be inhibited, cytotoxicity was lower (8%) than when 25% or less of the NK cells expressed KIR with matched HLA (49%) (p < 0.0001). Our data suggest that the interaction between inhibitory KIR and HLA ligands can be correlated to some extent with NK cell function, but measurement of NK activity may provide the best information for analysis of clinical situations.

Dietary supplementation with white button mushroom enhances natural killer cell activity in C57BL/6 mice

Mushrooms are reported to possess antitumor, antiviral, and antibacterial properties. These effects of mushrooms are suggested to be due to their ability to modulate immune cell functions. However, a majority of these studies evaluated the effect of administering extracts of exotic mushrooms through parental routes, whereas little is known about the immunological effect of a dietary intake of white button mushrooms, which represent 90% of mushrooms consumed in the U.S. In this study, we fed C57BL/6 mice a diet containing 0, 2, or 10% (wt/wt) white button mushroom powder for 10 wk and examined indices of innate and cell-mediated immunity. Mushroom supplementation enhanced natural killer (NK) cell activity, and IFNgamma and tumor necrosis factor-alpha (TNFalpha) production, but only tended to increase IL-2 (P = 0.09) and did not affect IL-10 production by splenocytes. There were significant correlations between NK activity and production of IFNgamma (r = 0.615, P < 0.001) and TNFalpha (r = 0.423, P = 0.032) in splenocytes. Mushroom supplementation did not affect macrophage production of IL-6, TNFalpha, prostaglandin E(2), nitric oxide, and H(2)O(2), nor did it alter the percentage of total T cells, helper T cells (CD4(+)), cytotoxic or suppressive T cells (CD8(+)), regulatory T cells (CD4(+)/CD25(+)), total B cells, macrophages, and NK cells in spleens. These results suggest that increased intake of white button mushrooms may promote innate immunity against tumors and viruses through the enhancement of a key component, NK activity. This effect might be mediated through increased IFNgamma and TNFalpha production.

Stromal-cell regulation of natural killer cell differentiation

Natural killer (NK) cells are bone-marrow-derived lymphocytes that play a crucial role in host defense against some viral and bacterial infections, as well as against tumors. Their phenotypic and functional maturation requires intimate interactions between the bone marrow stroma and committed precursors. In parallel to the identification of several phenotypic and functional stages of NK cell development, recent studies have shed new light on the role of stromal cells in driving functional maturation of NK cells. In this review, we provide an overview of the role of bone marrow microenvironment in NK cell differentiation.

Antigen-activated human T lymphocytes express cell-surface NKG2D ligands via an ATM/ATR-dependent mechanism and become susceptible to autologous NK- cell lysis

Recent evidence indicates that natural killer (NK) cells can negatively regulate T-cell responses, but the mechanisms behind this phenomenon as a consequence of NK-T-cell interactions are poorly understood. We studied the interaction between the NKG2D receptor and its ligands (NKG2DLs), and asked whether T cells expressed NKG2DLs in response to superantigen, alloantigen, or a specific antigenic peptide, and if this rendered them susceptible to NK lysis. As evaluated by FACS, the major histocompatibility complex (MHC) class I chain-related protein A (MICA) was the ligand expressed earlier on both CD4(+) and CD8(+) T cells in 90% of the donors tested, while UL16-binding protein-1 (ULBP)1, ULBP2, and ULBP3 were induced at later times in 55%-75% of the donors. By carboxyfluorescein diacetate succinimidyl ester (CFSE) labeling, we observed that NKG2DLs were expressed mainly on T cells that had gone through at least one division. Real-time reverse-transcription polymerase chain reaction confirmed the expression of all NKG2DLs, except ULBP4. In addition, T-cell activation stimulated phosphorylation of ataxia-telangiectasia mutated (ATM), a kinase required for NKG2DLs expression after DNA damage, and ATM/Rad3-related kinase (ATR) inhibitors blocked MICA induction on T cells with a mechanism involving NF-kappaB. Finally, we demonstrated that activated T cells became susceptible to autologous NK lysis via NKG2D/NKG2DLs interaction and granule exocytosis, suggesting that NK lysis of T lymphocytes via NKG2D may be an additional mechanism to limit T-cell responses.

The multifaceted roles of chemokines in malignancy

Tumor development and progression are multifactorial processes, regulated by a large variety of intrinsic and microenvironmental factors. A key role in cancer is played by members of the chemokine superfamily. Chemokines and their receptors are expressed by tumor cells and by host cells, in primary tumors and in specific metastatic loci. The effects of chemokines on tumorigenesis are diverse: While some members of the superfamily significantly support this process, others inhibit fundamental events required for tumor establishment and metastasis. The current review describes the multifaceted roles of chemokines in malignancy, addressing four major aspects of their activities: (1) inducing leukocyte infiltration to tumors and regulating immune functions, with emphasis on tumor-associated macrophages (and the chemokines CCL2, CCL5), T cells (and the chemokines CXCL9, CXCL10) and dendritic cells (and the chemokines CCL19, CCL20, CCL21); (2) directing the homing of tumor cells to specific metastatic sites (the CXCL12-CXCR4 axis); (3) regulating angiogenic processes (mainly the ELR(+)-CXC and non-ELR-CXC chemokines); (4) acting directly on the tumor cells to control their malignancy-related functions. Together, these different chemokine functions establish a net of interactions between the tumor cells and their microenvironment, and partly dictate the fate of the malignancy cascade.

MHC Class I Antigens and Immune Surveillance in Transformed Cells

MHC class I antigens play a crucial role in the interaction of tumor cells with the host immune system, in particular, in the presentation of peptides as tumor-associated antigens to cytotoxic lymphocytes (CTLs) and in the regulation of cytolytic activity of natural killer (NK) cells. In this review we discuss the role of MHC class I antigens in the recognition and elimination of transformed cells and in the generation of tumor immune escape routes when MHC class I losses occur in tumors. The different altered MHC class I phenotypes and their distribution in different human tumors are the main topic of this review. In addition, molecular defects that underlie MHC alterations in transformed cells are also described in detail. Future research directions in this field are also discussed, including the laboratory analysis of tumor MHC class I-negative variants and the possible restoration of MHC class I expression.

Psychologic stress, reduced NK cell activity, and cytokine dysregulation in women experiencing diagnostic breast biopsy

The purpose of this study was to evaluate a woman's psychological and immunological response to breast biopsy before and after the procedure. Women were enrolled into the study when notified of the need for breast biopsy. Psychological and immunological assessments were made at enrollment, on the day of breast biopsy, as well as 1 month and 4 months after notification of biopsy results. Psychological assessments demonstrated that perceived stress, anxiety, and mood disturbance were heightened before biopsy and remained elevated after biopsy regardless of the diagnosis. Immunologically, the women exhibited reduced natural killer cell activity and INF gamma production before biopsy with reductions significant 1 month after the procedure. In contrast, IL-4, IL-6, and IL-10 production were increased before and after the procedure with most significant increases prior to the procedure and continuing 1 month after the procedure. These results demonstrate that undergoing biopsy of the breast for cancer diagnosis is an emotional experience, characterized by increased perceived stress, anxiety, and mood disturbance. This emotional distress is accompanied by reduced NK cell activity and cytokine dysregulation. The psychological and immunological impact of breast biopsy is not transient, but persists well beyond the actual experience of the biopsy procedure. Noteworthy is the observation that women with benign or malignant biopsy results experienced similar psycho-immune consequences. Hence, these observations are of relevance not only to women diagnosed with malignancy, who face the challenges of cancer treatment and adaptation to illness, but also to women with benign biopsy findings.

Macrophages are essential for antitumour effects against weakly immunogenic murine tumours induced by class B CpG-oligodeoxynucleotides

We explored the mechanisms of class B CpG-oligodeoxynucleotide-induced antitumour effects against weakly immunogenic tumours. Treatment with CpG-oligodeoxynucleotide 1826 (CpG) induced similar antitumour effects in B16 melanoma-bearing immunocompetent C57BL/6 mice and T-cell-deficient severe combined immunodeficient (SCID) mice, and NXS2 neuroblastoma-bearing T-cell-depleted A/J mice. Both macrophages (Mphi) and natural killer (NK) cells from CpG-treated C57BL/6 mice could mediate cytotoxicity in vitro, suggesting that these cell types might control tumour growth in vivo. However, CpG treatment of SCID/beige mice or T-cell-depleted and NK-cell-depleted A/J mice still induced antitumour effects in vivo, arguing against a major role of NK cells in the antitumour effects of CpG in the absence of T cells. In contrast, CpG treatment of interferon-gamma knockout (IFN-gamma(-/-)) C57BL/6 mice resulted in no antitumour effects in vivo and no Mphi-mediated tumoristasis in vitro despite unaltered cytolytic function of NK cells in vitro. Moreover, Mphi inactivation by silica substantially reduced CpG-induced suppression of tumour growth in vivo, revealing an important role of Mphi in CpG-induced antitumour effects. The in vitro tumouritoxicity by CpG-stimulated Mphi (CpG-Mphi) correlated with tumour cell mitochondria dysfunction and involved nitric oxide (NO), tumour necrosis factor-alpha (TNF-alpha) and IFN-gamma, whereas interleukin-1alpha (IL-1alpha), IL-1beta, IFN-alpha, TNF-related apoptosis-inducing ligand and Fas ligand played insignificant roles in CpG-Mphi tumouritoxicity. Taken together, our results indicate that the growth control of weakly immunogenic tumours during CpG-immunotherapy is mediated predominantly by Mphi, rather than T cells or NK cells.

The effect of renal ischemia-reperfusion injury on expression of RAE-1 and H60 in mice kidney

INTRODUCTION

NKG2D, an activating receptor, may trigger NK and CD8+ T cells. Ligands for NKG2D and major histocompability complex class I chain-related antigen (MIC) have been reported to be expressed in rejected human renal allografts. MIC-NKG2D engagement may induce natural killer (NK) cell activation providing T-cell costimulation. We hypothesized that this interaction between innate and adaptive immunity may occur during kidney ischemia-reperfusion injury (IRI).

METHODS

Male C57BL/6 mice after right renal resection were subjected to 35 minutes of left renal ischemia: the ischemic group. Sham-operated mice underwent the same protocol without vascular occlusion. The sham and ischemic kidneys were removed at 2 to 7, 10, 14, or 28 days postoperatively. The normal, sham, and ischemic kidney tissues were collected for reverse-transcriptase polymerase chain reaction, and immunohistochemistry analysis of MIC homologues in mice (Rae-1 and H60).

RESULTS

Compared with no expression in sham control and normal kidneys, IRI caused mRNA expression of Rae-1 from 2 to 10 days postoperatively and protein expression of Rae-1 from 2 to 14 days postoperatively in ischemic kidneys. We observed no expression of H60 mRNA or protein in any kidney.

CONCLUSION

H60 transcripts have been reported to be present in the BALB/c background but not in C57BL/6. We found IRI did not cause H60 mRNA on protein expression in C57BL/6 kidneys. Rae-1 was absent in normal C57BL/6 kidneys. The IRI-induced expression of the NKG2D ligand, Rae-1, might activate NK and CD8+ T cells. Our results suggested that MIC may be an important link between innate and adaptive immunity in kidney IRI.

Activation and self-tolerance of natural killer cells

Natural killer (NK) cells are regulated by numerous stimulatory and inhibitory receptors that recognize various classes of cell surface ligands, some of which are expressed by normal healthy cells. We review two key issues in NK cell biology. How do NK cells achieve tolerance to healthy self-cells, despite great potential variability in inhibitory and stimulatory receptor engagement? How is the disease status of unhealthy cells translated into changes in ligand expression and consequent sensitivity to NK cell lysis? Concerning the second question, we review evidence that ligands for one key NK receptor, NKG2D, are induced by the DNA damage response, which is activated in cells exposed to genotoxic stress. Because cancer cells and some infected cells are subject to genotoxic stress, these findings suggest a new concept for how diseased cells are discriminated by the immune system. Second, we review studies that have overturned the prevalent notion that NK cells achieve self-tolerance by expressing inhibitory receptors specific for self-major histocompatibility complex class I molecules. A subset of NK cells lacks such receptors. These NK cells are hyporesponsive when stimulatory receptors are engaged, suggesting that alterations in signaling pathways that dampen stimulatory receptor signals contribute to self-tolerance of NK cells.

Receptor-ligand analyses define minimal killer cell Ig-like receptor (KIR) in humans

Interactions between inhibitory killer cell immunoglobulin-like receptors (iKIR) and human leukocyte antigen (HLA) class I molecules regulate natural killer (NK) cell responses to eliminate infected and transformed cells while maintaining tolerance to healthy cells. Unlinked polymorphic gene families encode KIR receptors and HLA class I ligands and their independent segregation results in a variable number and type of iKIR + HLA pairs inherited in individuals. The diversity in the co-inheritance of iKIR + HLA pairs and activating KIR (aKIR) genes in 759 unrelated individuals from four ethnic populations was analyzed. Every individual studied inherited a minimum of one iKIR + HLA pair; suggesting that major histocompatibility complex class I-dependent inhibitory KIR signaling is essential for human NK cell function. In contrast, 13.4% of the study group lacked all aKIR genes. Twenty percent of the study group carried only one of the four iKIR + HLA pairs. Interestingly, 3% of the study group carrying only KIR2DL3 + HLA-C1 as an iKIR + HLA pair lacked aKIR genes. These data suggest that a single iKIR can constitute the minimal KIR repertoire for human NK cells. Genotypes carrying an equal number of iKIR + HLA pairs and aKIR genes represented 20% of the study group. The remaining individuals had either a dominant inhibitory KIR genotype (iKIR + HLA > aKIR) or a dominant activating KIR genotype (iKIR + HLA < aKIR). Genotypes encoding these imbalanced inhibitory and activating interactions may contribute to susceptibility or resistance to human diseases.

Self-tolerance of natural killer cells

Natural killer (NK) cells, similar to other lymphocytes, acquire tolerance to self. This means that NK cells have the potential to attack normal self cells but that there are mechanisms to ensure that this does not usually occur. Self-tolerance is acquired by NK cells during their development, but the underlying molecular and cellular mechanisms remain poorly understood. Recent studies have produced important new information about NK-cell self-tolerance. Here, we review the evidence for and against possible mechanisms of NK-cell self-tolerance, with an emphasis on the role of MHC-specific receptors.

KIR3DL3 allelic diversity: six new alleles exhibit both conservative and non-conservative substitutions

KIR3DL3 alleles were characterized in two families and one unrelated individual. Based on exon 2-9 nucleotide sequences, six novel alleles, 3DL3*00402, *005, *006, *007, *00801, *00802, were identified bringing the total number of known alleles to 11. Compared with 3DL3*001, the six new alleles differ by from three to nine nucleotides and from three to four amino acids. The new alleles double the number of known polymorphic positions to 18 with variation in exons encoding the extracellular domains, transmembrane region, and a portion of the cytoplasmic tail. Many of the nucleotide substitutions are shared among alleles of 3DL3 or other KIR loci, but five were found only in single 3DL3 alleles. Comparison of intron sequences among individuals carrying the same allele showed a modest number of substitutions with the exception of 3DL3*001 which differed substantially in its intron sequences. Two alleles sharing coding region sequences, 3DL3*00201 and 3DL3*00202, were also substantially different in intron sequences.

Therapy-induced antibodies to MHC class I chain-related protein A antagonize immune suppression and stimulate antitumor cytotoxicity

The activation of NKG2D on innate and adaptive cytotoxic lymphocytes contributes to immune-mediated tumor destruction. Nonetheless, tumor cell shedding of NKG2D ligands, such as MHC class I chain-related protein A (MICA), results in immune suppression through down-regulation of NKG2D surface expression. Here we show that some patients who respond to antibody-blockade of cytotoxic T lymphocyte-associated antigen 4 or vaccination with lethally irradiated, autologous tumor cells engineered to secrete granulocyte-macrophage colony-stimulating factor generate high titer antibodies against MICA. These humoral reactions are associated with a reduction of circulating soluble MICA (sMICA) and an augmentation of natural killer (NK) cell and CD8(+) T lymphocyte cytotoxicity. The immunotherapy-induced anti-MICA antibodies efficiently opsonize cancer cells for dendritic cell cross-presentation, which is correlated with a diversification of tumor antigen recognition. The anti-MICA antibodies also accomplish tumor cell lysis through complement fixation. Together, these findings establish a key role for the NKG2D pathway in the clinical activity of cytotoxic T lymphocyte-associated antigen 4 antibody blockade and granulocyte-macrophage colony-stimulating factor secreting tumor cell vaccines. Moreover, these results highlight the therapeutic potential of anti-MICA antibodies to overcome immune suppression and effectuate tumor destruction in patients.

Natural killer cell differentiation driven by Tyro3 receptor tyrosine kinases

Although understanding of the function and specificity of many natural killer (NK) cell receptors is increasing, the molecular mechanisms regulating their expression during late development of NK cells remain unclear. Here we use representational difference analysis to identify molecules required for late NK cell differentiation. Axl protein tyrosine kinase, together with the structurally related receptors Tyro3 and Mer, were essential for NK cell functional maturation and normal expression of inhibitory and activating NK cell receptors. Also, all three receptors were expressed in maturing NK cells, the ligands of these receptors were produced by bone marrow stromal cells, and recombinant versions of these ligands drove NK cell differentiation in vitro. These results collectively suggest that Axl, Tyro3 and Mer transmit signals that are essential for the generation of a functional NK cell repertoire.

Tumor-infiltrating CD4+ T lymphocytes in early breast cancer reflect lymph node involvement

BACKGROUND

The role of immune system in the pathogenesis and progression of breast cancer is a subject of controversy, and this stimulated us to investigate the association of the immunophenotype of tumor-infiltrating lymphocytes in early breast cancer with the spread of tumor cells to axillary lymph nodes.

METHODS

Tumor samples from 23 patients with early breast cancer from the Department of Gynecology and Obstetrics of Ribeirão Preto Medical School (USP) were obtained at the time of biopsy and submitted to an enzyme-digestion procedure for the extraction of tumor-infiltrating lymphocytes. The lymphocytes extracted were analyzed by dual-color flow cytometry with monoclonal antibodies in these combinations: CD3 FITC/CD19 PE, CD3 FITC/CD4 PE, CD3 FITC/CD8 PE, and CD16/56 PerCP, which are specific for immunophenotyping of T and B lymphocytes, helper and cytotoxic T lymphocytes, and natural killer (NK) cells. The mean percentage of these cells was used for comparing groups of patients with or without lymph node metastasis.

RESULTS

The mean value for T-lymphocyte infiltration was 24.72 +/- 17.37%; for B-lymphocyte infiltration, 4.22 +/- 6.27%; for NK-cell infiltration, 4.41 +/- 5.22%, and for CD4(+) and CD8(+) T-lymphocyte infiltration, 12.43 +/- 10.12% and 11.30 +/- 15.09%, respectively. Only mean values of T- and CD4(+) T-lymphocyte infiltration were higher in the group of patients with lymph node metastasis, while no differences were noted in the other lymphocyte subpopulations.

CONCLUSION

The association of tumor-infiltrating CD4(+) T lymphocytes with lymph node metastasis suggests a role for these cells in the spread of neoplasia to lymph nodes in patients with early breast cancer.

Natural killer-dendritic cell cross-talk in cancer immunotherapy

Natural killer (NK) cells and dendritic cells (DCs), two important components of the immune system, can exchange bidirectional activating signals in a positive feedback. Myeloid DCs, the cell type specialised in the presentation of antigen and initiation of antigen-specific immune responses, have recently been documented to be involved in supporting innate immunity, promoting the production of cytokines and cytotoxicity of NK cells, and enhancing their tumouricidal activity. Natural interferon-producing cells/plasmacytoid DCs (IPCs/PDCs) play an additional role in NK cell activation. Reciprocally, NK cells, traditionally considered to be major innate effector cells, have also recently been shown to play immunoregulatory 'helper' functions, being able to activate DCs and to enhance their ability to produce pro-inflammatory cytokines, and to stimulate T helper (Th) 1 and cytotoxic T lymphocyte (CTL) responses of tumour-specific CD4+ and CD8+ T cells. Activated NK cells induce the maturation of myeloid DCs into stable type-1 polarised DCs (DC1), characterised by up to a 100-fold enhanced ability to produce IL-12p70 in response to subsequent interaction with Th cells. In addition, the ability of NK cells to kill tumour cells may facilitate the generation of tumour-related antigenic material, further accelerating the induction of tumour-specific immunity. DC1, induced by NK cells or by NK cell-related soluble factors, are stable, resistant to tumour-related suppressive factors, and demonstrate a strongly enhanced ability to induce Th1 and CTL responses in human in vitro and mouse in vivo models. Compared with the standard mature DCs that are used in clinical trials at present, human NK cell-induced DC1s act as superior inducers of anticancer CTL responses during in vitro sensitisation. This provides a strong rationale for the combined use of NK cells and DCs in the immunotherapy of patients with cancer and patients with chronic infections that are resistant to standard forms of treatment. Stage I/II clinical trials that are being implemented at present should allow evaluation of the immunological and clinical efficacy of combined NK-DC therapy of melanoma and other cancers.

BCR/ABL oncogene directly controls MHC class I chain-related molecule A expression in chronic myelogenous leukemia

MHC class I chain-related molecules (MIC) participate in immune surveillance of cancer through engagement of the NKG2D-activating receptor on NK and T cells. Decreased NKG2D expression and function upon chronic exposure to NKG2D ligands and/or soluble forms of MIC (sMIC) may participate in immune escape. In chronic myeloid leukemia, a malignancy caused by the BCR/ABL fusion oncoprotein, we showed cell surface expression of MICA on leukemic, but not healthy, donor hemopoietic CD34+ cells. At diagnosis, chronic myeloid leukemia patients had abnormally high serum levels of sMICA and weak NKG2D expression on NK and CD8+ T cells, which were restored by imatinib mesylate (IM) therapy. In the BCR/ABL+ cell line K562, IM decreased both surface MICA/B expression and NKG2D-mediated lysis by NK cells. Silencing BCR/ABL gene expression directly evidenced its role in the control of MICA expression. IM did not affect MICA mRNA levels, but decreased MICA protein production and release. Sucrose density gradient fractionation of K562 cytoplasmic extracts treated with IM showed a shift in the distribution of MICA mRNA from the polysomal toward the monosomal fractions, consistent with decreased translation. Among the major pathways activated by BCR/ABL that regulate translation, PI3K and mammalian target of rapamycin were shown to control MICA expression. These data provide evidence for direct control of MICA expression by an oncogene in human malignancy and indicate that posttranscriptional mechanisms may participate in the regulation of MICA expression.

Placenta-derived soluble MHC class I chain-related molecules down-regulate NKG2D receptor on peripheral blood mononuclear cells during human pregnancy: a possible novel immune escape mechanism for fetal survival

Mammalian pregnancy is an intriguing immunological phenomenon where the semiallogeneic fetus is not rejected. Tolerance toward the fetus involves a number of mechanisms associated with modifications of the immune status of the mother. In this study, we strongly suggest a novel mechanism for fetal evasion of maternal immune attack, based on the engagement and down-regulation of the activating NK cell receptor NKG2D on PBMC by soluble MHC class I chain-related proteins A and B (collectively termed MIC). A similar immune escape pathway was previously described in tumors. We found that MIC mRNA was constitutively expressed by human placenta and could be up-regulated upon heat shock treatment. Our immunomorphologic studies showed that the MIC expression in placenta was restricted to the syncytiotrophoblast. Immunoelectron microscopy revealed a dual MIC expression in the syncytiotrophoblast: on the apical and basal cell membrane and in cytoplasmic vacuoles as MIC-loaded microvesicles/exosomes. Soluble MIC molecules were present at elevated levels in maternal blood throughout normal pregnancy and were released by placental explants in vitro. Simultaneously, the cell surface NKG2D expression on maternal PBMC was down-regulated compared with nonpregnant controls. The soluble MIC molecules in pregnancy serum were able to interact with NKG2D and down-regulate the receptor on PBMC from healthy donors, with the consequent inhibition of the NKG2D-dependent cytotoxic response. These findings suggest a new physiological mechanism of silencing the maternal immune system that promotes fetal allograft immune escape and supports the view of the placenta as an immunoregulatory organ.

Escape strategies and reasons for failure in the interaction between tumour cells and the immune system: how can we tilt the balance towards immune-mediated cancer control?

The last decade has witnessed an exponential increase in the attempts to demonstrate that adaptive immunity can effectively detect cancer cells and impair their growth in vivo in cancer patients. However, clinical trials of immunotherapy with a broad array of immunisation strategies have depicted a rather disappointing scenario, suggesting that successful control of tumour growth by immunotherapeutic treatments may not be an easy task to achieve. The attention of tumour immunologists has thus been switched to the potential reasons of failure, and extensive efforts are being made in defining the cellular and molecular pathways interfering with the capacity of the immune system to develop powerful immunological reactions against tumour cells. Although many of these pathways have been well characterised in murine models, little and controversial information about their role in determining neoplastic progression in cancer patients is available. This discrepancy at the moment represents one of the major limitations in understanding the obstacles to the in vivo development of protective T cell-mediated immune responses against tumours, and how pharmacological or biological interventions aimed at bypassing tumour escape mechanisms would indeed result in a clinical benefit. The study of the reasons for the failure of the immune system to control tumour growth, which have to be ascribed to highly interconnected phenomena occurring at both tumour and immune levels, could in the near future provide adequate tools to fight cancer by finely tuning the host environment through biological therapies.