Creation of intercellular bonds by anchoring protein ligands to membranes using the diphtheria toxin T domain.

We describe the creation of cell adhesion mediated by cell surface engineering. The Flt3-ligand was fused to a membrane anchor made of the diphtheria toxin translocation domain. The fusion protein was attached to the surface of a cell by an acid pulse. Contact with another cell expressing the receptor Flt3 lead to its activation. This activity involved direct cell-cell contact. A mean force of 20 nN was needed to separate functionalized cells after 5 min of contact. Overall, we showed that it is possible to promote specific cell-cell adhesion by attaching protein ligands at the surface of cells.

NKp30 isoforms and NKp30 ligands are predictive biomarkers of response to imatinib mesylate in metastatic GIST patients.

Despite effective targeted therapy acting on KIT and PDGFRA tyrosine kinases, gastrointestinal stromal tumors (GIST) escape treatment by acquiring mutations conveying resistance to imatinib mesylate (IM). Following the identification of NKp30-based immunosurveillance of GIST and the off-target effects of IM on NK cell functions, we investigated the predictive value of NKp30 isoforms and NKp30 soluble ligands in blood for the clinical response to IM. The relative expression and the proportions of NKp30 isoforms markedly impacted both event-free and overall survival, in two independent cohorts of metastatic GIST. Phenotypes based on disbalanced NKp30B/NKp30C ratio (ΔBClow) and low expression levels of NKp30A were identified in one third of patients with dismal prognosis across molecular subtypes. This ΔBClow blood phenotype was associated with a pro-inflammatory and immunosuppressive tumor microenvironment. In addition, detectable levels of the NKp30 ligand sB7-H6 predicted a worse prognosis in metastatic GIST. Soluble BAG6, an alternate ligand for NKp30 was associated with low NKp30 transcription and had additional predictive value in GIST patients with high NKp30 expression. Such GIST microenvironments could be rescued by therapy based on rIFN-α and anti-TRAIL mAb which reinstated innate immunity.

Negative prognostic impact of regulatory T cell infiltration in surgically resected esophageal cancer post-radiochemotherapy.

Ever accumulating evidence indicates that the long-term effects of radiotherapy and chemotherapy largely depend on the induction (or restoration) of an anticancer immune response. Here, we investigated this paradigm in the context of esophageal carcinomas treated by neo-adjuvant radiochemotherapy, in a cohort encompassing 196 patients. We found that the density of the FOXP3+ regulatory T cell (Treg) infiltrate present in the residual tumor (or its scar) correlated with the pathological response (the less Tregs the more pronounced was the histological response) and predicted cancer-specific survival. In contrast, there was no significant clinical impact of the frequency of CD8+ cytotoxic T cells. At difference with breast or colorectal cancer, a loss-of-function allele of toll like receptor 4 (TLR4) improved cancer-specific survival of patients with esophageal cancer. While a loss-of-function allele of purinergic receptor P2X, ligand-gated ion channel, 7 (P2RX7) failed to affect cancer-specific survival, its presence did correlate with an increase in Treg infiltration. Altogether, these results corroborate the notion that the immunosurveillance seals the fate of patients with esophageal carcinomas treated with conventional radiochemotherapy.

Characterization of the Microenvironment in Positive and Negative Sentinel Lymph Nodes from Melanoma Patients.

Melanomas are aggressive skin tumors characterized by high metastatic potential. Our previous results indicate that Natural Killer (NK) cells may control growth of melanoma. The main defect of blood NK cells was a decreased expression of activating NCR1/NKp46 receptor and a positive correlation of NKp46 expression with disease outcome in stage IV melanoma patients was found. In addition, in stage III melanoma patients, we identified a new subset of mature NK cells in macro-metastatic Lymph nodes (LN). In the present studies, we evaluated the numbers of NK cells infiltrating primary cutaneous melanoma and analyzed immune cell subsets in a series of sentinel lymph nodes (SLN). First, we show that NKp46+ NK cells infiltrate primary cutaneous melanoma. Their numbers were related to age of patients and not to Breslow thickness. Then, a series of patients with tumor-negative or -positive sentinel lymph nodes matched for Breslow thickness of the cutaneous melanoma was constituted. We investigated the distribution of macrophages (CD68), endothelial cells, NK cells, granzyme B positive (GrzB+) cells and CD8+ T cells in the SLN. Negative SLN (SLN-) were characterized by frequent adipose involution and follicular hyperplasia compared to positive SLN (SLN+). High densities of macrophages and endothelial cells (CD34), prominent in SLN+, infiltrate SLN and may reflect a tumor favorable microenvironment. Few but similar numbers of NK and GrzB+ cells were found in SLN- and SLN+: NK cells and GrzB+ cells were not correlated. Numerous CD8+ T cells infiltrated SLN with a trend for higher numbers in SLN-. Moreover, CD8+ T cells and GrzB+ cells correlated in SLN- not in SLN+. We also observed that the numbers of CD8+ T cells negatively correlated with endothelial cells in SLN-. The numbers of NK, GrzB+ or CD8+ T cells had no significant impact on overall survival. However, we found that the 5 year-relapse rate was higher in SLN with higher numbers of NK cells.

Obesity and renal cancer: Role of adipokines in the tumor-immune system conflict.

Epidemiological studies link obesity, as measured by increased body mass index (BMI) to the incidence of renal cell carcinoma (RCC) as well as to the cancer-related mortality of RCC patients. RCC is the third cancer most robustly associated with increased BMI. Understanding the role of the adipose tissue in renal carcinogenesis is therefore of major importance for the development of novel paradigms of RCC prevention and treatment. Here, we discuss the current knowledge on the impact of obesity on the development and progression of RCC as well as the role of adipose tissue-derived hormones (adipokines) in the conflict between growing tumors and the immune system.

NK cells sense tumors, course of disease and treatments: Consequences for NK-based therapies.

The recent findings on NK activation indicate that these cells are important antitumor effectors. NK cells participate in the graft-vs.-leukemia effect to control the relapse in leukemic patients transplanted with allogeneic hematopoietic stem cells. In various tumors, correlation between NK cell infiltrates and prognosis were reported. However, tumor-infiltrating NK cells are yet poorly characterized. We here summarize our results and the recent studies of the literature on tumor-infiltrating NK cells, and discuss the impact of these novel insights into NK cell responses against tumors for the design of NK cell-based therapies.

Unique functional status of natural killer cells in metastatic stage IV melanoma patients and its modulation by chemotherapy.

PURPOSE: Immunotherapy is an alternative for metastatic melanoma patients resistant to chemotherapy. Natural killer (NK) cells are powerful antileukemia effectors and their role in solid tumors is suspected. NK cell activation is regulated by a balance between activating receptors, which detect stress molecules on tumor cells, and HLA-I specific inhibitory receptors. Here, we studied the phenotype and function of NK cells in stage IV metastatic melanoma patients. EXPERIMENTAL DESIGN: Circulating NK cells from 35 healthy donors and 51 patients were studied: 24 patients before chemotherapy (prechemotherapy), 17 patients 1 month after 1 to 4 lines of chemotherapy (postchemotherapy), and 10 patients analyzed pre- and postchemotherapy. NK functionality was carried out toward 2 primary metastatic melanoma cell lines, analyzed for the expression of NK receptor ligands. RESULTS: NK cells from prechemotherapy patients exhibit an NKp46(dim)/NKG2A(dim) phenotype. In contrast, NK cells from postchemotherapy patients display high expression of NKp46 and NKG2A receptors. Purified NK cells from patients are efficiently activated in response to melanoma cells. Melanoma cells express different level of NKG2D ligands and HLA-I molecules. In agreements with their phenotype, NK cells from pre- and postchemotherapy patients present distinct functional status toward these primary melanoma cells. A dynamic label free assay was used to determine the pathways involved in the lysis of melanoma cells by IL-2-activated NK cells. NKG2D, NCR (natural cytotoxicity receptor), and DNAM-1 are involved in the NK-mediated lysis of melanoma cells. CONCLUSIONS: These results provide new arguments and clues to design NK cell-based immunotherapeutic strategies for melanoma patients.

Serum soluble HLA-E in melanoma: a new potential immune-related marker in cancer.

BACKGROUND: Tumor-derived soluble factors, including soluble HLA molecules, can contribute to cancer immune escape and therefore impact on clinical course of malignant diseases. We previously reported that melanoma cells produce, in vitro, soluble forms of the non-classical MHC class I molecule HLA-E (sHLA-E). In order to investigate sHLA-E production by various tumors and to address its potential value as a tumor-associated marker, we developed a specific ELISA for the quantification of sHLA-E in biological fluids. METHODOLOGY/PRINCIPAL FINDINGS: We developed a sHLA-E specific and sensitive ELISA and we showed that serum sHLA-E levels were significantly elevated (P<0.01) in melanoma patients (n = 127), compared with healthy donors (n = 94). sHLA-E was also detected in the culture supernatants of a wide variety of tumor cell lines (n = 98) including melanomas, kidney, colorectal and breast cancers. Cytokines regulation of sHLA-E production by tumor cells was also carried out. IFN-γ, IFN-α and TNF-α were found to upregulate sHLA-E production by tumor cells. CONCLUSIONS/SIGNIFICANCE: In view of the broad tumor tissue release of HLA-E and its up-regulation by inflammatory cytokines, sHLA-E should be studied for its involvement in immune responses against tumors. Interestingly, our results demonstrated a positive association between the presence of serum sHLA-E and melanoma. Therefore, the determination of sHLA-E levels, using ELISA approach, may be investigated as a clinical marker in cancer patients.

Human renal cancer cells express a novel membrane-bound interleukin-15 that induces, in response to the soluble interleukin-15 receptor alpha chain, epithelial-to-mesenchymal transition.

Although interleukin-15 (IL-15) is a powerful immunomodulatory factor that has been proposed for cancer immunotherapy, its intratumoral expression may be correlated with tumor progression and/or poor clinical outcome. Therefore, neoplasias potentially sensitive to immunotherapy should be checked for their IL-15 expression and function before choosing immunotherapy protocols. Primary human renal cancer cells (RCC) express a novel form of membrane-bound IL-15 (mb-IL-15), which displays three major original properties: (a) It is expressed as a functional membrane homodimer of 27 kDa, (b) it is shed in the extracellular environment by the metalloproteases ADAM17 and ADAM10, and (c) its stimulation by soluble IL-15 receptor alpha (s-IL-15Ralpha) chain triggers a complex reverse signal (mitogen-activated protein kinases, FAK, pMLC) necessary and sufficient to ~induce epithelial-mesenchymal transdifferentiation (EMT), a crucial process in tumor progression whose induction is unprecedented for IL-15. In these cells, complete EMT is characterized by a dynamic reorganization of the cytoskeleton with the subsequent generation of a mesenchymal/contractile phenotype (alpha-SMA and vimentin networks) and the loss of the epithelial markers E-cadherin and ZO-1. The retrosignaling functions are, however, hindered through an unprecedented cytokine/receptor interaction of mb-IL-15 with membrane-associated IL-15Ralpha subunit that tunes its signaling potential competing with low concentrations of the s-IL-15Ralpha chain. Thus, human RCC express an IL-15/IL-15R system, which displays unique biochemical and functional properties that seem to be directly involved in renal tumoral progression.

Deciphering membrane insertion of the diphtheria toxin T domain by specular neutron reflectometry and solid-state NMR spectroscopy.

Insertion and translocation of soluble proteins into and across biological membranes are involved in many physiological and pathological processes, but remain poorly understood. Here, we describe the pH-dependent membrane insertion of the diphtheria toxin T domain in lipid bilayers by specular neutron reflectometry and solid-state NMR spectroscopy. We gained unprecedented structural resolution using contrast-variation techniques that allow us to propose a sequential model of the membrane-insertion process at angstrom resolution along the perpendicular axis of the membrane. At pH 6, the native tertiary structure of the T domain unfolds, allowing its binding to the membrane. The membrane-bound state is characterized by a localization of the C-terminal hydrophobic helices within the outer third of the cis fatty acyl-chain region, and these helices are oriented predominantly parallel to the plane of the membrane. In contrast, the amphiphilic N-terminal helices remain in the buffer, above the polar headgroups due to repulsive electrostatic interactions. At pH 4, repulsive interactions vanish; the N-terminal helices penetrate the headgroup region and are oriented parallel to the plane of the membrane. The C-terminal helices penetrate deeper into the bilayer and occupy about two thirds of the acyl-chain region. These helices do not adopt a transmembrane orientation. Interestingly, the T domain induces disorder in the surrounding phospholipids and creates a continuum of water molecules spanning the membrane. We propose that this local destabilization permeabilizes the lipid bilayer and facilitates the translocation of the catalytic domain across the membrane.

Behavior of the N-terminal helices of the diphtheria toxin T domain during the successive steps of membrane interaction.

During intoxication of a cell, the translocation (T) domain of the diphtheria toxin helps the passage of the catalytic domain across the membrane of the endosome into the cytoplasm. We have investigated the behavior of the N-terminal region of the T domain during the successive steps of its interaction with membranes at acidic pH using tryptophan fluorescence, its quenching by brominated lipids, and trypsin digestion. The change in the environment of this region was monitored using mutant W281F carrying a single native tryptophan at position 206 at the tip of helix TH1. The intrinsic propensity to interact with the membrane of each helix of the N-terminus of the T domain, TH1, TH2, TH3, and TH4, was also studied using synthetic peptides. We showed the N-terminal region of the T domain was not involved in the binding of the domain to the membrane, which occurred at pH 6 mainly through hydrophobic effects. At that stage of the interaction, the N-terminal region remained strongly solvated. Further acidification eliminated repulsive electrostatic interactions between this region and the membrane, allowing its penetration into the membrane by attractive electrostatic interactions and hydrophobic effects. The peptide study indicated the nature of forces contributing to membrane penetration. Overall, the data suggested that the acidic pH found in the endosome not only triggers the formation of the molten globule state of the T domain required for membrane interaction but also governs a progressive penetration of the N-terminal part of the T domain in the membrane. We propose that these physicochemical properties are necessary for the translocation of the catalytic domain.

Concerted protonation of key histidines triggers membrane interaction of the diphtheria toxin T domain.

The translocation domain (T domain) of the diphtheria toxin contributes to the transfer of the catalytic domain from the cell endosome to the cytosol, where it blocks protein synthesis. Translocation is initiated when endosome acidification induces the interaction of the T domain with the membrane of the compartment. We found that the protonation of histidine side chains triggers the conformational changes required for membrane interaction. All histidines are involved in a concerted manner, but none is indispensable. However, the preponderance of each histidine varies according to the transition observed. The pair His(223)-His(257) and His(251) are the most sensitive triggers for the formation of the molten globule state in solution, whereas His(322)-His(323) and His(251) are the most sensitive triggers for membrane binding. Interestingly, the histidines are located at key positions throughout the structure of the protein, in hinges and at the interface between each of the three layers of helices forming the domain. Their protonation induces local destabilizations, disrupting the tertiary structure and favoring membrane interaction. We propose that the selection of histidine residues as triggers of membrane interaction enables the T domain to initiate translocation at the rather mild pH found in the endosome, contributing to toxin efficacy.