Laurent Gros

Transgenic mice overexpressing insulin-like growth factor-II in β cells develop type 2 diabetes

During embryonic development, insulin-like growth factor-II (IGF-II) participates in the regulation of islet growth and differentiation. We generated transgenic mice (C57BL6/SJL) expressing IGF-II in β cells under control of the rat Insulin I promoter in order to study the role of islet hyperplasia and hyperinsulinemia in the development of type 2 diabetes. In contrast to islets from control mice, islets from transgenic mice displayed high levels of IGF-II mRNA and protein. Pancreases from transgenic mice showed an increase in β-cell mass (about 3-fold) and in insulin mRNA levels. However, the organization of cells within transgenic islets was disrupted, with glucagon-producing cells randomly distributed throughout the core. We also observed enhanced glucose-stimulated insulin secretion and glucose utilization in islets from transgenic mice. These mice displayed hyperinsulinemia, mild hyperglycemia, and altered glucose and insulin tolerance tests, and about 30% of these animals developed overt diabetes when fed a high-fat diet. Furthermore, transgenic mice obtained from the N1 backcross to C57KsJ mice showed high islet hyperplasia and insulin resistance, but they also developed fatty liver and obesity. These results indicate that local overexpression of IGF-II in islets might lead to type 2 diabetes and that islet hyperplasia and hypersecretion of insulin might occur early in the pathogenesis of this disease.

Inhibition of CD39 Enzymatic Function at the Surface of Tumor Cells Alleviates Their Immunosuppressive Activity

Bastid and colleagues show that CD39 is highly expressed on tumor-infiltrating lymphocytes, tumor stroma, but also on tumor cells; treatment with CD39 inhibitors or blocking antibody alleviated the tumor-induced inhibition of T-cell proliferation and increased CTL- and NK cell–mediated cytotoxicity. The ectonucleotidases CD39 and CD73 hydrolyze extracellular adenosine triphosphate (ATP) and adenosine diphosphate (ADP) to generate adenosine, which binds to adenosine receptors and inhibits T-cell and natural killer (NK)–cell responses, thereby suppressing the immune system. The generation of adenosine via the CD39/CD73 pathway is recognized as a major mechanism of regulatory T cell (Treg) immunosuppressive function. The number of CD39+ Tregs is increased in some human cancers, and the importance of CD39+ Tregs in promoting tumor growth and metastasis has been demonstrated using several in vivo models. Here, we addressed whether CD39 is expressed by tumor cells and whether CD39+ tumor cells mediate immunosuppression via the adenosine pathway. Immunohistochemical staining of normal and tumor tissues revealed that CD39 expression is significantly higher in several types of human cancer than in normal tissues. In cancer specimens, CD39 is expressed by infiltrating lymphocytes, the tumor stroma, and tumor cells. Furthermore, the expression of CD39 at the cell surface of tumor cells was directly demonstrated via flow cytometry of human cancer cell lines. CD39 in cancer cells displays ATPase activity and, together with CD73, generates adenosine. CD39+CD73+ cancer cells inhibited the proliferation of CD4 and CD8 T cells and the generation of cytotoxic effector CD8 T cells (CTL) in a CD39- and adenosine-dependent manner. Treatment with a CD39 inhibitor or blocking antibody alleviated the tumor-induced inhibition of CD4 and CD8 T-cell proliferation and increased CTL- and NK cell–mediated cytotoxicity. In conclusion, interfering with the CD39–adenosine pathway may represent a novel immunotherapeutic strategy for inhibiting tumor cell–mediated immunosuppression. Cancer Immunol Res; 3(3); 254–65. ©2014 AACR.

A Crucial Role for Infected-Cell/Antibody Immune Complexes in the Enhancement of Endogenous Antiviral Immunity by Short Passive Immunotherapy

Antiviral monoclonal antibodies (mAbs) represent promising therapeutics. However, most mAbs-based immunotherapies conducted so far have only considered the blunting of viral propagation and not other possible therapeutic effects independent of virus neutralization, namely the modulation of the endogenous immune response. As induction of long-term antiviral immunity still remains a paramount challenge for treating chronic infections, we have asked here whether neutralizing mAbs can, in addition to blunting viral propagation, exert immunomodulatory effects with protective outcomes. Supporting this idea, we report here that mice infected with the FrCasE murine retrovirus on day 8 after birth die of leukemia within 4–5 months and mount a non-protective immune response, whereas those rapidly subjected to short immunotherapy with a neutralizing mAb survive healthy and mount a long-lasting protective antiviral immunity with strong humoral and cellular immune responses. Interestingly, the administered mAb mediates lysis of infected cells through an antibody-dependent cell cytotoxicity (ADCC) mechanism. In addition, it forms immune complexes (ICs) with infected cells that enhance antiviral CTL responses through FcγR-mediated binding to dendritic cells (DCs). Importantly, the endogenous antiviral antibodies generated in mAb-treated mice also display the same properties, allowing containment of viral propagation and enhancement of memory cellular responses after disappearance of the administered mAb. Thus, our data demonstrate that neutralizing antiviral mAbs can act as immunomodulatory agents capable of stimulating a protective immunity lasting long after the end of the treatment. They also show an important role of infected-cells/antibody complexes in the induction and the maintenance of protective immunity through enhancement of both primary and memory antiviral T-cell responses. They also indicate that targeting infected cells, and not just viruses, by antibodies can be crucial for elicitation of efficient, long-lasting antiviral T-cell responses. This must be considered when designing antiviral mAb-based immunotherapies.

Tumor antigen-targeting monoclonal antibody-based immunotherapy: Orchestrating combined strategies for the development of long-term antitumor immunity

Tumor antigen (TA)-targeting monoclonal antibody (mAb)-based treatments are considered to be one of the most successful strategies in cancer therapy. Besides targeting TAs and inducing tumor cell death, such antibodies interact with immune cells through Fc-dependent mechanisms to induce adaptive memory immune responses. However, multiple inhibitory/immunosuppressive pathways can be induced by tumor cells to limit the establishment of an efficient antitumor response and consequently a sustained clinical response to TA-targeting mAbs. Here, we provide an overview on how TA-targeting mAbs in combination with conventional cancer therapies and/or inhibitors of key immunosuppressive pathways might represent promising approaches to achieve long-term tumor control.

Control of regulatory T cells is necessary for vaccine-like effects of antiviral immunotherapy by monoclonal antibodies

Regulatory T cells (Tregs) down-regulate immunity and are associated with chronic viral infections, suggesting that their inhibition might be used to treat life-threatening diseases. Using the FrCasE mouse retroviral model, we have recently shown that short mAb-based immunotherapies can induce life-long protective immunity. This finding has a potentially important therapeutical impact because mAbs are increasingly used to treat severe viral infections. We now report that poor anti-FrCasE immunity in infected mice is due to Treg expansion in secondary lymphoid organs because depletion of Tregs restored humoral and cytotoxic T lymphocyte (CTL) antiviral responses. Kinetic analyses show that Treg expansion is not a consequence of chronicity, but rather is associated with viral spread. Moreover, Treg adoptive transfers indicate that production of the immunosuppressive cytokine IL-10 is essential for preventing a protective immune response. Finally, treatment of infected mice with a virus-neutralizing IgG2a shortly after infection prevents Treg expansion and limits immunosuppressive activity. This effect is rapid, necessary for the development of protective immunity, and depends on mAb effector functions. Therefore, manipulating Tregs may be necessary to confer robust antiviral immunity in the context of mAb-based therapy. This concept likely applies to cancer treatment because vaccine-like effects of mAbs have also been observed in certain cancer immunotherapies.

Induction of Long-Term Protective Antiviral Endogenous Immune Response by Short Neutralizing Monoclonal Antibody Treatment

ABSTRACT Long-term immune control of viral replication still remains a major challenge in retroviral diseases. Several monoclonal antibodies (MAbs) have already shown antiviral activities in vivo, including in the clinic but their effects on the immune system of treated individuals are essentially unknown. Using the lethal neurodegeneration induced in mice upon infection of neonates by the FrCasE retrovirus as a model, we report here that transient treatment by a neutralizing MAb shortly after infection can, after an immediate antiviral effect, favor the development of a strong protective host immune response containing viral propagation long after the MAb has disappeared. In vitro virus neutralization- and complement-mediated cell lysis assays, as well as in vivo viral challenges and serum transfer experiments, indicate a clear and essential contribution of the humoral response to antiviral protection. Our observation may have important therapeutic consequences as it suggests that short antibody-based therapies early after infection should be considered, at least in the case of maternally infected infants, as adjunctive treatment strategies against human immunodeficiency virus, not only for a direct effect on the viral load but also for favoring the emergence of an endogenous antiviral immune response.

Efficient Mother-to-Child Transfer of Antiretroviral Immunity in the Context of Preclinical Monoclonal Antibody-Based Immunotherapy

ABSTRACT When mice under the age of 5 to 6 days are infected, the FrCasE retrovirus induces a neurodegenerative disease leading to death within 1 to 2 months. We have recently reported that transient treatment with a neutralizing monoclonal antibody (MAb) shortly after infection, in addition to an expected immediate decrease in the viral load, also favors the development of a strong protective immune response that persists long after the MAb has been cleared. This observation may have important therapeutic consequences, as it suggests that MAbs might be used, not only as direct neutralizing agents, but also as immunomodulatory agents enabling patients to mount their own antiviral immune responses. We have investigated whether immunoglobulins from mothers who displayed a strong anti-FrCasE humoral response induced upon MAb treatment could affect both viremia and the immune systems of FrCasE-infected pups till adult age upon placental and/or breastfeeding transfer. The strongest effects, i.e., reduction in the viral load and induction of protective humoral antiviral responses, were observed upon breastfeeding alone and breastfeeding plus placental immunity transfer. However, placental transfer of anti-FrCasE antibodies was sufficient to both protect neonatally infected animals and help them initiate a neutralizing anti-FrCasE response. Also, administration of a neutralizing MAb to naive mothers during late gestation and breastfeeding could generate similar effects. Taken together, our data support the concept that passive immunotherapies during late gestation and/or breastfeeding might help retrovirally infected neonates prime their own protective immune responses, in addition to exerting an immediate antiviral effect.

Monoclonal Antibody-based Genetic Immunotherapy

The clinical application potential of monoclonal antibodies concerns a wide range of diseases including, among others, viral infections, cancer and autoimmune diseases. Intravenous injection is a simple and obvious mode of administration of purified therapeutic antibodies to patients but may not always be appropriate for long-term treatments for a variety of reasons. One limitation concerns the elevated costs of recombinant proteins certified for human use. Moreover, hour-long infusions require a hospital environment and are often associated with mild to very severe side effects. This makes large-scale clinical applications of a number of monoclonal antibodies with demonstrated therapeutic activity impossible or, at least, severely compromised. In vivo production of therapeutic antibodies in patients, through either genetic modification of their tissues or implantation of antibody-producing cells, might represent an attractive alternative to overcome these drawbacks. Moreover, this method should also provide other benefits. Continuous and sustained delivery of antibodies at a low, but therapeutic level should prevent, or at least delay, induction of neutralizing anti-idiotypic immune responses, which sometimes develop when massive doses of purified immunoglobulins are repeatedly injected into patients. Additionally, it should also limit variations in the bioavailability of therapeutic antibodies that are often detrimental to the efficacy of treatments. The present review reports on the recent developments of gene/cell therapies aiming at the in vivo production and systemic delivery of monoclonal antibodies with the final goal of treating severe chronic diseases.

Monoclonal Antibody 667 Recognizes the Variable Region A Motif of the Ecotropic Retrovirus CasBrE Envelope Glycoprotein and Inhibits Env Binding to the Viral Receptor

ABSTRACT Monoclonal antibody (MAb) 667 is a neutralizing mouse monoclonal antibody recognizing the envelope glycoprotein (Env) of the ecotropic neurotropic murine retrovirus CasBrE but not that of other murine retroviruses. Since 667 can be used for preclinical studies of antiviral gene therapy as well as for studying the early events of retroviral infection, we have cloned its cDNAs and molecularly characterized it in detail. Spot technique-based experiments showed that 667 recognizes a linear epitope of 12 amino acids located in the variable region A of the receptor binding domain. Alanine scanning experiments showed that six amino acids within the epitope are critical for MAb binding. One of them, D57, is not present in any other murine retroviral Env, which suggests a critical role for this residue in the selectivity of 667. MAb 667 heavy- and light-chain cDNAs were functionally characterized by transient transfection into Cos-7 cells. Enzyme-linked immunosorbent assays and Biacore studies showed that the specificities as well as the antigen-binding thermodynamic and kinetic properties of the recombinant 667 MAb (r667) produced by Cos-7 cells and those of the parental hybridoma-produced MAb (h667) were similar. However, h667 was shown to contain contaminating retroviral and/or retrovirus-like particles which interfere with both viral binding and neutralization experiments. These contaminants could successfully be removed by a stringent purification protocol. Importantly, this purified 667 could completely prevent retrovirus binding to target cells and was as efficient as the r667 MAb produced by transfected Cos-7 cells in neutralization assays. In conclusion, this study shows that the primary mechanism of virus neutralization by MAb 667 is the blocking of the retroviral receptor binding domain of CasBrE Env. In addition, the findings of this study constitute a warning against the direct use of hybridoma cell culture supernatants for studying the initial events of retroviral cell infection as well as for carrying out in vivo neutralization experiments and suggest that either recombinant antibodies or highly purified antibodies are preferable for these purposes.

Inhibition of ATP-sensitive K+ channels by substituted benzo[c]quinolizinium CFTR activators

The substituted benzo[c]quinolizinium compounds MPB-07 and MPB-91 are novel activators of the cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel. High homologies between CFTR and the sulfonylurea receptor (SUR), which associates with the potassium channel Kir6.2 to form the ATP-sensitive K(+) (K(ATP)) channel, prompted us to examine possible effects of these compounds on K(ATP) channels using electrophysiological recordings and binding assays. Activity of recombinant K(ATP) channels expressed in Xenopus oocytes was recorded in the inside-out configuration of the patch-clamp technique. Channels were practically unaffected by MPB-07 but were fully blocked by MPB-91 with half-inhibition achieved at approximately 20 microM MPB-91. These effects were similar on channels formed by Kir6.2, and either the SUR1 or SUR2A isoforms were independent of the presence of nucleotides. They were not influenced by SUR mutations known to interfere with its nucleotide-binding capacity. MPB-91, but not MPB-07, was able to displace binding of glibenclamide to HEK cells expressing recombinant SUR1/Kir6.2 channels. Glibenclamide binding to native channels from pancreatic MIN6 cells was also displaced by MPB-91. A Kir6.2 mutant able to form channels without SUR was also blocked by MPB-91, but not by MPB-07. These observations demonstrate that neither MPB-07 nor MPB-91 interact with SUR, in spite of its high homology with CFTR, and that MPB-91 blocks K(ATP) channels by binding to the Kir6.2 subunit. Thus, caution should be exercised when planning to use MPB compounds in cystic fibrosis therapy, specially MPB-91 which could nonetheless find interesting applications as the precursor of a new class of K channel blockers.