Andrea Acebes-Huerta

NKG2D signaling in cancer immunosurveillance

The immune system is able to detect and eliminate transformed cells. The activating receptor NKG2D is particularly relevant for cancer immunosurveillance. NKG2D ligand expression renders tumor cells more susceptible to be killed by NK and T cells, and correlates with the clinical outcome of the disease. However, tumors develop mechanisms to overcome the NKG2D‐mediated immune response, which has been associated with poor prognosis and impairment of the clinical benefits of immunotherapy in many human cancers. The highly specific pattern of expression displayed by the NKG2D ligands, mainly confined to tumor cells, together with the strong immune response triggered by this receptor clearly supports the idea that the NKG2D‐mediated pathway may be a powerful target for the treatment of cancer. This review draws together the most recent discoveries concerning the biology of the NKG2D signaling and their therapeutic relevance in the context of cancer.

Prognostic significance of CD8 and CD4 T cells in chronic lymphocytic leukemia

The prognostic value of the number of T cells and NK cells at diagnosis in CLL was analyzed in a cohort of 256 patients with CLL diagnosed between 1997 and 2007. Patients with leukemia showed elevated NK cells and T cell populations and CD4/CD8 ratio was inverted in 39.7% cases. Prognostic significance of lymphocytes was analyzed as a ratio of relative number of T cells to the size of the malignant monoclonal B-cell pool (T/NK cells:Malignant monoclonal B-cells ratio). Patients showed higher relative number of CD4 (p = 0.03), CD8 (p = 0.02), and NK cells (p = 0.01) in early Rai stage of disease. The multivariate Cox analysis identified the relative number of CD8 (hazard ratio (HR) = 1.464; p = 0.006) and CD4 T cells (HR = 0.091; p < 0.01) as independent predictors for survival. Additionally, patients with relative CD8 count > 0.074 or CD4 count > 0.1 had higher 10-year overall survival than patients with CD8 count ≤ 0.074 or CD4 count ≤ 0.1 (p = 0.002). Higher CD8 count was associated with significantly higher median time of survival of patients (149.33 vs. 82.06 months). Finally, association of the good prognostic factor of leukemia cells (CD38−) with high relative CD8 count identified a group of patients with an indolent clinical course with an overall survival probability at 10 years of 95%.

Molecular Bases for the Regulation of NKG2D Ligands in Cancer

NKG2D is an activating receptor expressed by NK and T cells primarily involved in the elimination of transformed and infected cells. NKG2D ligands are self-proteins restrictedly expressed in healthy tissues, but induced in response to signaling pathways commonly associated with transformation. Proliferative, tumor suppressor, and stress signaling pathways linked to the tumorigenic process induce the expression of NKG2D ligands, initiating an immune response against the incipient tumor. Nevertheless, the activity of NKG2D ligands is counter-regulated in vivo by the immunoediting of cancer cells, resulting in the expression of multiple mechanisms of immune evasion in advanced tumors. The redundancy of NKG2D ligands, besides increasing the complexity of their regulation, may impair the generation of these immune evasion mechanisms. In this review, we attempt to integrate the mechanisms and pathways involved in the regulation of NKG2D ligand expression in cancer.

Expansion of NK Cells and Reduction of NKG2D Expression in Chronic Lymphocytic Leukemia. Correlation with Progressive Disease

The immune system may mediate anti-tumor responses in chronic lymphocytic leukemia (CLL) which may affect disease progression and survival. In this study, we analyzed the immune characteristics of 99 consecutive previously diagnosed CLL patients and 50 healthy controls. The distribution of lymphocyte subsets at diagnosis was retrospectively analyzed. Compared with controls, leukemia patients showed an expansion of NK and CD8 T cells at diagnosis. The relative number of CD8 T cells at diagnosis was associated with time to treatment, suggesting that CD8 T cells may modify disease progression. The distribution of lymphocyte subsets was analyzed again when patients were enrolled in this study. The median time since these patients were diagnosed was 277 weeks. Compared with diagnosis, the absolute number of CD8 T cells significantly decreased in these patients, reaching similar values to healthy controls; however NK cells kept significantly elevated overtime. Nevertheless, NK cells showed an impaired expression of NKG2D receptor and a defective cytotoxic activity. This down-regulation of NKG2D expression was further enhanced in patients with advanced and progressive disease. Additionally, membrane NKG2D levels significantly decreased on CD8 T cells, but a significant increase of NKG2D+CD4+ T cells was observed in CLL patients. The cytotoxic activity of NK cells was diminished in CLL patients; however the treatments with IL-2, IL-15, IL-21 and lenalidomide were able to restore their activity. The effect of IL-2 and IL-15 was associated with the increase of NKG2D expression on immune cells, but the effect of IL-21 and lenalidomide was not due to NKG2D up-regulation. The expansion of NK cells and the reversibility of NK cell defects provide new opportunities for the immunotherapeutic intervention in CLL.

Lenalidomide Induces Immunomodulation in Chronic Lymphocytic Leukemia and Enhances Antitumor Immune Responses Mediated by NK and CD4 T Cells

Lenalidomide is an immunomodulatory drug with therapeutic activity in chronic lymphocytic leukemia (CLL). However, it has pleiotropic effects, and the mechanism of action responsible for its therapeutic activity has not been well defined yet. Herein, we show that lenalidomide treatment does not have an effect on the proliferation of leukemia cells, but it increases the proliferation of B cells from healthy donors. Lenalidomide did not exert a direct effect on the apoptosis of leukemia cells obtained from CLL patients, although it indirectly induced their apoptosis through the activation of nonmalignant immune cells. Thus, lenalidomide markedly increased the proliferation of NK and CD4 T cells. The effect of lenalidomide on NK cells was secondary to the induction of IL-2 production by CD4 T cells. Accordingly, depletion of T cells or blockade of IL-2 activity completely abrogated the proliferation of NK cells. Additionally, lenalidomide enhanced NK and NKT-like cell-mediated natural cytotoxicity against leukemia cells from CLL patients. Lenalidomide also upregulated CD20 expression on leukemia cells and, accordingly, it had a synergistic effect with rituximab on promoting antibody-dependent cell-mediated cytotoxicity against primary leukemia cells. Overall, these observations provide a support for combining lenalidomide with rituximab as a treatment in CLL.

Expression of ERp5 and GRP78 on the membrane of chronic lymphocytic leukemia cells: association with soluble MICA shedding

MICA is a ligand of the activating receptor NKG2D, expressed by NK and T cells. MICA expression is induced in cancer cells favoring their elimination by the immune system; however, many advanced tumors shed soluble MICA (sMICA), which impairs NKG2D-mediated cytotoxicity. ERp5 and GRP78 are endoplasmic reticulum-resident proteins that are translocated to the surface of epithelial tumor cells where they interact with MICA and are involved in sMICA shedding. In this study, we analyze the role of ERp5 and GRP78 in sMICA shedding in chronic lymphocytic leukemia (CLL). Immunofluorescence and flow cytometry analyses showed that ERp5 and GRP78 were significantly expressed on the surface of B cells and leukemia cells, but they were not expressed on T cells. The expression of ERp5 and GRP78 was significantly higher in leukemia cells than in B cells from controls. ERp5 and GRP78 co-localized with MICA on the surface of leukemia cells and the levels of expression of ERp5 and GRP78 correlated with the level of expression of membrane-bound MICA in CLL patients. Associated with higher expression of membrane-bound ERp5 and GRP78, serum sMICA levels were approximately threefold higher in patients than in controls. Elevated sMICA levels in CLL patients were associated with the down-modulation of NKG2D surface expression on CD8 T cells. Finally, pharmacological inhibition of B cell lines and stimulated leukemia cells showed that ERp5 activity is involved in sMICA shedding in CLL. In conclusion, these results uncover a molecular mechanism which regulates MICA protein shedding and immune evasion in CLL.

Drug-induced hyperploidy stimulates an antitumor NK cell response mediated by NKG2D and DNAM-1 receptors

ABSTRACT Formation of polyploid or aneuploid cells is a pathological hallmark of malignant tumors. Cell cycle checkpoint mechanisms play a crucial role in ensuring genomic integrity during mitosis, avoiding the generation of aneuploid cells. Additionally, cancer cell DNA ploidy is subjected to extrinsic controls operated by activation of adaptive immune responses mediated by T cells. NK cells exert a central role in the innate anticancer immunity; however, the mechanisms involved in the recognition of tumor cells by NK cells have not been fully elucidated. Herein, we report that drug-induced polyploidy in cancer cells activates antitumor responses mediated by NK cells. Thus, hyperploidy-inducing chemotherapeutic agents strongly upregulate the tumor expression of ligands for the NK cell activating receptors NKG2D and DNAM-1. Drug-induced hyperploidy modulated the repertoire of activating receptors and the cytokine profile of NK cells, rendering tumor cells more susceptible to NK cell-mediated lysis through the activation of NKG2D and DNAM-1 receptors. In addition, hyperploidization stimulated the production of IL-2 by CD4 T cells, which induced NK cell proliferation and activity. The stimulation of MICA, a key NKG2D ligand, in hyperploid cells was mainly mediated by ATM protein kinase. Likewise, pharmacological inhibition of key regulators of endoplasmic reticulum stress in certain cell models supports a role for this pathway in NKG2D ligand upregulation. Overall, our findings indicate that, besides the cytotoxic effect on tumor cells, the therapeutic activity of anti-mitotic drugs may be mediated by the induction of a coordinated antitumor immune response involving NK and T cells.

Lenalidomide and Chronic Lymphocytic Leukemia

Lenalidomide is an oral immunomodulatory drug used in multiple myeloma and myelodysplastic syndrome and most recently it has shown to be effective in the treatment of various lymphoproliferative disorders such as chronic lymphocytic leukemia (CLL) and non-Hodgkin lymphoma. The mechanism of action of lenalidomide varies depending on the pathology, and in the case of CLL, it appears to primarily act by restoring the damaged mechanisms of tumour immunosurveillance. This review discusses the potential mechanism of action and efficacy of lenalidomide, alone or in combination, in treatment of CLL and its toxic effects such as tumor lysis syndrome (TLS) and tumor flare reaction (TFR), that make its management different from other hematologic malignancies.

Regulation of NKG2D signaling during the epithelial-to-mesenchymal transition

The plasma membrane receptor natural killer group 2 member D (NKG2D) underpins a major mechanism whereby natural killer (NK) and T cells recognize malignant cells. We have recently demonstrated that the epithelial-to-mesenchymal transition, one of the first steps of metastatic dissemination, is under the control of an immunological checkpoint that relies on NKG2D-mediated immune responses.

Analysis of clinical prognostic variables for Chronic Lymphocytic Leukemia decision-making problems

INTRODUCTION Chronic Lymphocytic Leukemia (CLL) is a disease with highly heterogeneous clinical course. A key goal is the prediction of patients with high risk of disease progression, which could benefit from an earlier or more intense treatment. In this work we introduce a simple methodology based on machine learning methods to help physicians in their decision making in different problems related to CLL. MATERIAL AND METHODS Clinical data belongs to a retrospective study of a cohort of 265 Caucasians who were diagnosed with CLL between 1997 and 2007 in Hospital Cabueñes (Asturias, Spain). Different machine learning methods were applied to find the shortest list of most discriminatory prognostic variables to predict the need of Chemotherapy Treatment and the development of an Autoimmune Disease. RESULTS Autoimmune disease occurrence was predicted with very high accuracy (>90%). Autoimmune disease development is currently an unpredictable severe complication of CLL. Chemotherapy Treatment has been predicted with a lower accuracy (80%). Risk analysis showed that the number of false positives and false negatives are well balanced. CONCLUSIONS Our study highlights the importance of prognostic variables associated with the characteristics of platelets, reticulocytes and natural killers, which are the main targets of the autoimmune haemolytic anemia and immune thrombocytopenia for autoimmune disease development, and also, the relevance of some clinical variables related with the immune characteristics of CLL patients that are not taking into account by current prognostic markers for predicting the need of chemotherapy. Because of its simplicity, this methodology could be implemented in spreadsheets.