Search

BackgroundThere is a clear need for targeted therapies to treat acute myeloid leukemia (AML), the most common acute leukemia in adults. CD123 (IL-3 receptor alpha chain) is an attractive target for AML treatment.1 However, cytotoxic antibody targeting CD123 proved insufficiently effective in a combination setting in phase II/III clinical trials.2 T-cell engagers targeting CD123 displayed some clinical efficacy but were often associated with cytokine release syndrome and neurotoxicity.3 Interest in the use of NK cells for therapeutic interventions has increased in recent years, as a potential safer alternative to T cells. Several NK-cell activating receptors, such as CD16a, NKG2D, and the natural cytotoxicity receptors NKp30 and NKp46, can be targeted to induce antitumor immunity. We previously reported the development of trifunctional NK-cell engagers (NKCEs) targeting a tumor antigen on cancer cells and co-engaging NKp46 and CD16a on NK cells.4MethodsWe report here the design, characterization and preclinical development of a novel trifunctional NK cell engager (NKCE) targeting CD123 on AML cells and engaging the activating receptors NKp46 and CD16a on NK cells. The CD123 NKCE therapeutic molecule was engineered with humanized antibodies targeting NKp464 and CD123.5 We compared CD123-NKCE and a cytotoxic ADCC-enhanced antibody (Ab) targeting CD123, in terms of antitumor activity in vitro, ex vivo and in vivo. Pharmacokinetic, pharmacodynamic and safety profile of CD123-NKCE were evaluated in non-human primate (NHP) studies.ResultsThe expression of the high affinity Fc gamma receptor CD64 on patient-derived AML cells inhibited the ADCC of the Ab targeting CD123 in vitro and ex vivo, but not the antitumor activity of CD123-NKCE. CD123-NKCE had potent antitumor activity against primary AML blasts and AML cell lines, promoted strong NK-cell activation and induced cytokine secretion only in the presence of AML target cells. Its antitumor activity in mouse model was greater than that of the comparator antibody. Moreover, CD123-NKCE had strong and prolonged pharmacodynamic effects in NHP when used at very low doses, was well-tolerated up to high 3 mg/kg dose and triggered only minor cytokine release.ConclusionsThe data for activity, safety, pharmacokinetics, and pharmacodynamics provided here demonstrate the superiority of CD123-NKCE over comparator cytotoxic antibody, in terms of antitumor activity in vitro, ex vivo, in vivo, and its favorable safety profile, as compared to T-cell therapies. These results constitute proof-of-principle for the efficacy of CD123-NKCE for controlling AML tumors in vivo, and provide consistent support for their clinical development.ReferencesEhninger A, Kramer M, Rollig C, et al. Distribution and levels of cell surface expression of CD33 and CD123 in acute myeloid leukemia. Blood Cancer J 2014;4:e218.Montesinos P, Gail J Roboz GJ, et al. Safety and efficacy of talacotuzumab plus decitabine or decitabine alone in patients with acute myeloid leukemia not eligible for chemotherapy: results from a multicenter, randomized, phase 2/3 study. Leukemia 2021;35(1):62–74.Uy GL, Aldoss I, Foster MC, et al. Flotetuzumab as salvage immunotherapy for refractory acute myeloid leukemia. Blood 2021;137(6):751–762.Gauthier L, Morel A, Anceriz N, et al. Multifunctional natural killer cell engagers targeting NKp46 trigger protective tumor immunity. Cell 2019;177(7):1701–13.Jin L, Lee EM, Ramshaw HS, et al. Monoclonal antibody-mediated targeting of CD123, IL-3 receptor alpha chain, eliminates human acute myeloid leukemic stem cells. Cell Stem Cell 2009;5:31–42.

Background Coronavirus disease 2019 (COVID-19) is a new pandemic disease caused by infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The C5a anaphylatoxin and its receptor C5aR1 (CD88) play a key role in the initiation and maintenance of several inflammatory responses, by recruiting and activating neutrophils and monocytes in the lungs. Methods We provide a longitudinal analysis of immune responses, including immune cell phenotyping and assessments of the soluble factors present in the blood and broncho-alveolar lavage fluid (BALF) of patients at various stages of COVID-19 severity: paucisymptomatic, pneumonia and acute respiratory distress syndrome (ARDS) Results We report an increase in soluble C5a levels proportional to COVID-19 severity and high levels of C5aR1 expression in blood and pulmonary myeloid cells, supporting a role for the C5a-C5aR1 axis in the pathophysiology of ARDS. Avdoralimab, an anti-C5aR1 therapeutic monoclonal antibodies (mAbs) prevented C5a-mediated human myeloid cell recruitment and activation, and inhibited acute lung injury (ALI) in human C5aR1 knockin mice. Conclusions These results support the evaluation of avdoralimab to block C5a-C5aR1 axis as a mean of limiting myeloid cell infiltration in damaged organs and preventing the excessive lung inflammation and endothelialitis associated with ARDS in COVID-19 patients Acknowledgements The Explore COVID-19 IPH group, the Explore COVID-19 Marseille Immunopole group. Ethics Approval Human study protocol was approved by the Committee for the Protection of Persons Ile-de-France III – France (#2020-A00757-32). Animal experiments were approved by the ministere de l’enseignement superieur, de la recherche et de l’innovation – France (APAFIS#25418-2020051512242806 v2).

Coronavirus disease 2019 (COVID-19) is a new pandemic acute respiratory disease caused by infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)11-3. We provide here a longitudinal analysis of immune responses, including immune cell phenotyping and assessments of the soluble factors present in the blood and broncho-alveolar lavage fluid (BALF) of patients at various stages of COVID-19 severity: paucisymptomatic, pneumonia and acute respiratory distress syndrome (ARDS). While we confirm a lymphopenia associated with COVID-19 severity4-7, we report an increase in expression of the NKG2A and PD-1 inhibitory receptors on T and natural killer (NK) cells, as well as an increase in CD39 expression on NK cells, suggesting that therapeutic blocking antibodies targeting these molecules already used for cancer immunotherapy8 could be repurposed as first line of defense to promote SARS-CoV-2 clearance. In addition, the C5a anaphylatoxin and its receptor C5aR1 (CD88) play a key role in the initiation and maintenance of inflammatory responses, by recruiting neutrophils and monocytes to the lungs9,10. We report an increase in soluble C5a levels proportional to COVID-19 severity and high levels of C5aR1 expression in blood and BALF myeloid cells, indicating a potential role of the C5a-C5aR1 axis in the pathophysiology of ARDS. Avdoralimab is a clinical-stage anti-C5aR1 therapeutic monoclonal antibody (mAb) that prevents C5a-mediated myeloid cell recruitment and activation. We propose the use of this antibody to limit myeloid cell infiltration in the lung and to prevent the excessive lung inflammation associated with ARDS in COVID-19 patients.

BackgroundMost immunomodulatory approaches have focused on enhancing T-cell responses, with immune checkpoint inhibitors, chimeric antigen receptor T cells or bispecific antibodies. Although these therapies have led to exceptional successes, only a minority of cancer patients benefit from these treatments, highlighting the need to identify new cells and molecules that could be exploited in the next generation of immunotherapy. Given the crucial role of innate immune responses in immunity, harnessing these responses opens up new possibilities for tumor control. Antibody engineering provides us with great opportunities to induce synthetic immunity and to optimize the biological functions of innate immune cells, in particular by boosting the capacity of Natural Killer (NK) cells to kill tumor cells directly and to stimulate T-cell responses indirectly.MethodsIn order to leverage the advantages of harnessing NK cell effector functions, we used our Antibody-based NK cell Engager Therapeutics (ANKET) molecular platform1 and designed a new generation of molecules that can engage activating receptors NKp46 and CD16, the IL-2Rβ chain and a tumor antigen in a single tetra-specific molecule (ANKET4). The variant of interleukin-2 (IL-2v) integrated in the ANKET4 molecule is unable to bind the α-subunit of its receptor to limit regulatory T cell activation and IL-2Rα-mediated toxicity.ResultsIn vitro, ANKET4 provides proliferation and activation signals targeted to NK cells and induces primary human NK cell cytolytic activity and the secretion of cytokines and chemokines only after binding to the tumor target. In mouse models of both invasive and solid tumors, ANKET4 induced NK cell proliferation and accumulation at the tumor bed, and had a higher anti-tumor efficacy than approved therapeutic antibodies targeting the same tumor antigen. Mechanistically, transcriptomic analysis and in-vivo studies revealed that the geometry of the ANKET4 molecule including NKp46, CD16 and IL-2 receptor binding moieties on the same molecule was essential for its strong activity which results from a synthetic cooperativity between immunoreceptor tyrosine-based activation motif (ITAM) and cytokine signaling pathways. In non-human primates, CD20-directed ANKET4 resulted in sustained CD20+ B-cell depletion with minimal systemic cytokine release and no clinical sign of toxicity.ConclusionsTetra-specific ANKET4 thus constitutes a technological platform combining the induction of NK cell proliferation and effector functions with a manageable safety profile, supporting its clinical development for next-generation cancer immunotherapies.ReferenceGauthier L, Morel A, Anceriz N, Rossi B, Blanchard-Alvarez A, Grondin G, et al. Multifunctional natural killer cell engagers targeting NKp46 trigger protective tumor immunity. Cell 2019;177(7):1701–13 e16.Ethics ApprovalPrimary immune cells were purified from buffy coats from healthy donors obtained from Etablissement Francais du Sang (EFS, Marseille) with written consent from each volunteer.All mouse experiments were performed in accordance with the rules of the Innate Pharma ethics committee and were approved by the Ministère de l’Enseignement Supérieur, de la Recherche et de l’Innovation – France (APAFIS# 19272 ).All non human-primate procedures were conducted according to European guidelines for animal care and use for scientific purposes (Directive 63-2010, ”Journal Officiel des Communautés Européennes”, L276, September 22, 2010) and according to CEA institutional guidelines. The study was approved by the local ethical committee under the number A18_080 and by the French Administration (APAFIS#20525-2019050616506478 v1)

Background: MICA and MICB are tightly regulated stress-induced proteins that trigger the immune system by binding to the activating receptor NKG2D on cytotoxic lymphocytes. MICA and MICB are highly polymorphic molecules with prevalent expression on several types of solid tumors and limited expression in normal/healthy tissues, making them attractive targets for therapeutic intervention. Methods: We have generated a series of anti-MICA and MICB cross-reactive antibodies with the unique feature of binding to the most prevalent isoforms of both these molecules. Results: The anti-MICA and MICB antibody MICAB1, a human IgG1 Fc-engineered monoclonal antibody (mAb), displayed potent antibody-dependent cellular cytotoxicity (ADCC) and antibody-dependent cellular phagocytosis (ADCP) of MICA/B-expressing tumor cells in vitro. However, it showed insufficient efficiency against solid tumors in vivo, which prompted the development of antibody-drug conjugates (ADC). Indeed, optimal tumor control was achieved with MICAB1-ADC format in several solid tumor models, including patient-derived xenografts (PDX) and carcinogen-induced tumors in immunocompetent MICAgen transgenic mice. Conclusions: These data indicate that MICA and MICB are promising targets for cytotoxic immunotherapy.

New therapies that promote antitumour immunity have been recently developed. Most of these immunomodulatory approaches have focused on enhancing T-cell responses, either by targeting inhibitory pathways with immune checkpoint inhibitors, or by targeting activating pathways, as with chimeric antigen receptor T cells or bispecific antibodies. Although these therapies have led to unprecedented successes, only a minority of patients with cancer benefit from these treatments, highlighting the need to identify new cells and molecules that could be exploited in the next generation of immunotherapy. Given the crucial role of innate immune responses in immunity, harnessing these responses opens up new possibilities for long-lasting, multilayered tumour control.

Summary: Immune checkpoint inhibitors have revolutionized cancer treatment. However, many cancers are resistant to ICIs, and the targeting of additional inhibitory signals is crucial for limiting tumor evasion. The production of adenosine via the sequential activity of CD39 and CD73 ectoenzymes participates to the generation of an immunosuppressive tumor microenvironment. In order to disrupt the adenosine pathway, we generated two antibodies, IPH5201 and IPH5301, targeting human membrane-associated and soluble forms of CD39 and CD73, respectively, and efficiently blocking the hydrolysis of immunogenic ATP into immunosuppressive adenosine. These antibodies promoted antitumor immunity by stimulating dendritic cells and macrophages and by restoring the activation of T cells isolated from cancer patients. In a human CD39 knockin mouse preclinical model, IPH5201 increased the anti-tumor activity of the ATP-inducing chemotherapeutic drug oxaliplatin. These results support the use of anti-CD39 and anti-CD73 monoclonal antibodies and their combination with immune checkpoint inhibitors and chemotherapies in cancer. : The production of adenosine via CD39 and CD73 ectoenzymes participates in an immunosuppressive tumor microenvironment. Perrot et al. generated two antibodies, IPH5201 and IPH5301, targeting human CD39 and CD73, respectively. In vitro and in vivo data support the use of anti-CD39 and anti-CD73 mAbs in combination cancer therapies. Keywords: CD39, CD73, cancer immunotherapies, therapeutic antibodies, adenosine pathway, tumor micro-environment, immunosuppression

Summary Over the last decade, various new therapies have been developed to promote anti-tumor immunity. Despite interesting clinical results in hematological malignancies, the development of bispecific killer-cell-engager antibody formats directed against tumor cells and stimulating anti-tumor T cell immunity has proved challenging, mostly due to toxicity problems. We report here the generation of trifunctional natural killer (NK) cell engagers (NKCEs), targeting two activating receptors, NKp46 and CD16, on NK cells and a tumor antigen on cancer cells. Trifunctional NKCEs were more potent in vitro than clinical therapeutic antibodies targeting the same tumor antigen. They had similar in vivo pharmacokinetics to full IgG antibodies and no off-target effects and efficiently controlled tumor growth in mouse models of solid and invasive tumors. Trifunctional NKCEs thus constitute a new generation of molecules for fighting cancer. Video Abstract

O1 IL-15 primes an mTOR-regulated gene-expression program to prolong anti-tumor capacity of human natural killer cells #### Andreas Lundqvist1, Vincent van Hoef1, Xiaonan Zhang1, Erik Wennerberg2, Julie Lorent1, Kristina Witt1, Laia Masvidal Sanz1, Shuo Liang1, Shannon Murray3, Ola Larsson1

The discovery of a targeted therapeutic compound along with its companion predictive biomarker is a major goal of clinical development for a personalized anticancer therapy to date. Here we present evidence of the predictive value of TLR3 expression by tumor cells for the efficacy of Poly (A:U) dsRNA in 194 breast cancer patients enrolled in a randomized clinical trial. Adjuvant treatment with double-stranded RNA (dsRNA) was associated with a significant decrease in the risk of metastatic relapse in TLR3 positive but not in TLR3-negative breast cancers. Moreover, we show the functional relevance of TLR3 expression by human tumor cells for the antitumor effects mediated by dsRNA in several preclinical mouse models carried out in immunocompromised animals. These 2 independent lines of evidence relied upon the generation of a novel tool, an anti-TLR3 antibody (40F9.6) validated for routine detection of TLR3 expression on paraffin-embedded tissues. Altogether, these data suggest that dsRNA mediates its therapeutic effect through TLR3 expressed on tumor cells, and could therefore represent an effective targeted treatment in patients with TLR3-positive cancers. Cancer Res; 71(5); 1607–14. ©2011 AACR.

The concept of immunogenic chemotherapy that has recently emerged relies upon the capacity of a cytotoxic compound to trigger a cell-death modality. This modality elicits cross-priming by dendritic cells of tumor antigen-specific T cells that will contribute to the tumoricidal activity of the compound and protect the host against relapse. In contrast, most anticancer drugs elicit nonimmunogenic apoptosis that is not accompanied with an immunizing property. This review will discuss some molecular and metabolic changes required at the level of the tumor that must engage key pathways at the level of the host for the induction of Tc1 polarized–protective T cell responses during chemotherapy. We will summarize the immune adjuvants that can boost the immunogenicity of cell death to augment the efficacy of chemotherapy.

Within the tumor microenvironment, adenosine causes immune suppression and dysregulation of immune cell infiltrates resulting in tumor spreading. Adenosine accumulation results from the hydrolysis of extracellular immunoactivating ATP and ADP into AMP by the CD39 (ENTPD1) ectonucleotidase. AMP can be further hydrolyzed into immunosuppressive Adenosine (Ado) by CD73 (NT5E), a cell membrane ectonucleotidase of the NTPDase family.The immunosuppressive role of CD39 expressed on both Tregs and tumor cells has been demonstrated in several reports. Conversely, CD73 expression in the tumor environment has been associated with poor disease outcome and/or with a pro-metastatic phenotype. Blockade of CD39 and CD73 may promote anti-tumor immunity directly by accumulating immunostimulating ATP for CD39 and indirectly by reducing adenosine accumulation for both targets.In cancer tissue, using IHC and flow cytometry analyses, we observed that while CD73 is often expressed by tumor cells, CD39 is more frequently up-regulated on tumor infiltrating cells compared to PBMC or adjacent non-tumor tissue. We next describe the discovery and preclinical development of a unique anti-huCD39 blocking antibody and of an anti-human CD73 antibody for cancer immunotherapy. These anti-CD39 and anti-CD73 antibodies specifically bind with high affinity to huCD39 and huCD73 proteins, respectively. They potently inhibit enzyme activity of their respective targets under their soluble and membrane-associated forms, without inducing down-modulation of these enzymes expressed at the cell surface. Innate's antibodies efficiently reverse Ado-mediated T cell suppression in vitro in presence of ATP and both CD39- and CD73-expressing immune cells and additionally exhibit unique features. The anti-CD39 Ab maintains high concentration of ATP in the extracellular compartment that enhances DC activation and subsequent T cell proliferation in vitro. The anti-CD73 blocking Ab exhibits a more potent ability to block soluble and membrane-associated CD73 enzyme activity than benchmark Abs currently in clinical development. Finally, in vivo blockade of ATP/Ado pathway in CD39ko mice resulted in improved anti-tumor efficacy of immunogenic cell death inducer chemotherapy and of immune checkpoint therapies, including PD1 and CTLA4.Taken together, these data support the clinical development of anti-CD39 and anti-CD73 neutralizing Abs for cancer immunotherapy, potentially in combination with chemotherapy or Immune Checkpoint therapy. The humanized anti-huCD39 and anti-huCD73 monoclonal antibodies are currently in preclinical development.The research leading to CD73 results were obtained within the TumAdoR collaborative consortium that received funding from the European Community's Seventh Framework Program (FP7/2007-2013) under grant agreement n°602200. Citation Format: Ivan Perrot, Marc Giraudon Paoli, Séverine Augier, Marilyne Royannez Blemont, Marion Gaudin, Frédéric Bosco, Rachel Courtois, Stephane Delahaye, Diana Jecko, Nicolas Gourdin, Maryline Salin Agu, Cyril Perrier, Paul Ricaut, Aurélie Docquier, Stéphanie Chanteux, Benjamin Rossi, Agnès Représa, Caroline Denis, Romain Remark, Cécile Bonnafous, Laurent Gauthier, Ariane Morel, Nathalie Bonnefoy, Jérémy Bastid, Yannis Morel, Carine Paturel. Preclinical development of humanized CD39 and CD73 blocking antibodies targeting the ATP/adenosine immune checkpoint pathway for cancer immunotherapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2718.

Siglec-9 is a MHC class I-independent inhibitory receptor expressed on NK and myeloid cells (including dendritic cells, monocytes and neutrophils). Its ligands are sialic acid-containing carbohydrates which are over-expressed on various tumor types compared to normal tissues (1). Sialylation of tumor cells is involved in tumor cell malignancy and is reported for decades as a mechanism of escape from immune surveillance (2). The loss of beta-2-microglobulin, an essential component of MHC class I antigen presentation, was recently described as a common mechanism of resistance to checkpoint blockade in clinical trials and revealed the need for MHC class I-independent therapies (3-4). Thus, Siglec-9-sialic acid interaction disruption may promote anti-tumor immunity independently of MHC class I expression by tumors. Here, we describe the discovery and characterization of first-in class anti-human Siglec-9 antibodies as new checkpoint blockade therapy in a wide range of cancers. Antibodies were discovered that efficiently block the interaction between Siglec-9 and its ligands. Epitope mapping revealed that antibodies bind to distinct epitopes on Siglec-9 near the sialic acid binding site. In vitro assays showed that they potently reverse inhibitory functions of Siglec-9 on NK cells leading to subsequent sialic acid-expressing tumor cell killing. Interestingly, Siglec-9 is enhanced on both CD4+ and CD8+ T cells from RCC, melanoma and NSCLC PBMC patients suggesting a putative additional role on adaptive immunity. Siglec-9 was also co-expressed with other inhibitory receptors on NK cells and combination with other immune checkpoint blockers in in vitro assays is ongoing. The antibodies displaying the most interesting features were successfully humanized. (1) Pathol Oncol Res. 2016 Jul;22(3):443-7 (2) Nature. 1968 Jun 29;218(5148):1254-5 (3) Nat Commun. 2017 Oct 26;8(1):1136 (4) N Engl J Med. 2016 Sep 1;375(9):819-29 Citation Format: Olivier Bénac, Marion Gaudin, Mélody Ors, Aude Le Roy, Hélène Rispaud Blanc, Caroline Soulas, Stéphanie Chanteux, Benjamin Rossi, Laurent Gauthier, Carine Paturel, Yannis Morel, Ivan Perrot, Stéphanie Cornen. Preclinical development of first-in-class antibodies targeting Siglec-9 immune checkpoint for cancer immunotherapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2713.

Metastatic renal cell carcinoma, inherently resistant to conventional treatments, is considered immunogenic. Indeed, partial responses are obtained after treatment with cytokines such as IL-2 or IFN-alpha, suggesting that the immune system may control the tumor growth. In this study, we have investigated the ability of the main subset of peripheral gammadelta lymphocytes, the Vgamma9Vdelta2-TCR T lymphocytes, to induce an effective cytotoxic response against autologous primary renal cell carcinoma lines. These gammadelta T cells were expanded ex vivo using a Vgamma9Vdelta2 agonist, a synthetic phosphoantigen called Phosphostim. From 11 of 15 patients, the peripheral Vgamma9Vdelta2 T cells were amplified in vitro by stimulating PBMCs with IL-2 and Phosphostim molecule. These expanded Vgamma9Vdelta2 T cells express activation markers and exhibit an effector/memory phenotype. They display a selective lytic potential toward autologous primary renal tumor cells and not against renal NC. The lytic activity involves the perforin-granzyme pathway and is mainly TCR and NKG2D receptor dependent. Furthermore, an increased expression of MHC class I-related molecule A or B proteins, known ligands of NKG2D, are detected on primary renal tumor cells. Interestingly, from 2 of the 11 positive cultures in response to Phosphostim, expanded-Vgamma9Vdelta2 T cells present an expression of killer cell Ig-like receptors, suggesting their prior recruitment in vivo. Unexpectedly, on serial frozen sections from three tumors, we observe a gammadelta lymphocyte infiltrate that was mainly composed of Vgamma9Vdelta2 T cells. These results outline that Vgamma9Vdelta2-TCR effectors may represent a promising approach for the treatment of metastatic renal cell carcinoma.

LIGHT is a recently identified member of the TNF superfamily that is up-regulated on activated T cells and can cooperate with CD40L to condition DC for the priming of CTL. In this report, we show that an intracellular pool of LIGHT is found selectively in some CD45RA-CD27+CD4+ "central" memory T cells and to a greater extent in some CD45RA-CD27-CD4+ effector memory T cells. LIGHT, like CD40L, is rapidly up-regulated on memory CD4+ T cells upon activation. Unlike CD40L, LIGHT up-regulation on naive T cells is delayed. Stimulation of DC with each subset of memory T cells in the presence of superantigen revealed that CD40L and LIGHT are required for optimal secretion of IL-12. Moreover, effector memory T cells, which can interact with DC in peripheral tissues, contribute to CCR7 induction on DC. LIGHT and CD40L can also regulate IL-12 production by CCR7+ DC capable of migration to lymph nodes. These data suggest that both LIGHT and CD40L may be involved in the maintenance or reactivation of secondary Th1 responses.

MICA and MICB, and ULPB1-6, are ligands for NKG2D, an activating receptor expressed on NK cells and subsets of T cells. Expression of MICA and MICB is induced by cellular stress in transformed tumor cells, upon infections or at sites of chronic inflammation. Their expression is tightly regulated by complex mechanisms both at the mRNA and protein levels. As markers of cellular stress and tumorigenesis, MICA and MICB proteins are attractive candidates for targeting by a cytotoxic antibody. Moreover, ionizing radiation and various chemotherapies that cause cellular stress have been shown to induce expression of NKG2D ligands, opening interesting options for combination therapies. MICA and MICB are also compelling targets for immunomodulation. MICA and -B cause internalization of NKG2D, leading to reduced cell surface NKG2D levels and desensitization of cytotoxic effector cells in cancer patients. It was recently reported that blockade of the interactions between NKG2D and its ligands could lead to significant anti-tumor responses in mouse models. Moreover, NKG2D ligand expression was induced on immunosuppressive macrophages in cancer patients and in mouse tumor models, raising the possibility that anti-MICA/B antibodies may be used to counter local immunosuppression by targeting myeloid derived suppressor cells. We have selected the IPH4301 antibody for its ability to bind to all allotypes of MICA and MICB, and for its dual action as an immunomodulatory agent, as well as direct cytotoxicity towards MICA/B-expressing tumor cells. First, IPH4301 induces killing of MICA/B expressing tumor cells through antibody-dependent cell cytotoxicity (ADCC) and antibody-dependent cell phagocytosis (ADCP) measured towards MICA expressing cells in vitro. In vivo ADCC/ADCP efficacy was demonstrated in several preventive and curative settings using MICA expressing cell lines or endogenous tumors. Second, IPH4301 blocks the binding of MICA/B to NKG2D. In a tumor context of chronic triggering, NKG2D downmodulation has been described in several studies of cancer patients. This modulation is mainly induced by expression of MICA/B, and less by the ULBPs. By blocking the MICA/NKG2D interaction, IPH4301 effectively restored NKG2D expression and function in vitro on primary NK and T cells. Third, we show that IPH4301 can override immunosuppression induced by suppressive myeloid cells. In vitro differentiated M2 macrophages, but not M1 macrophages, have the capacity to impair cytotoxic functions of autologous NK cells towards MICA expressing tumor cell lines. This suppression could be overcome by IPH4301, which triggered ADCC by these otherwise impaired NK cells. Altogether, IPH4301 is a novel, first-in-class anti-MICA/B mAb with both cytotoxic and immunomodulatory properties. Ongoing work aims to perform regulatory toxicology studies and manufacture a clinical grade product for testing in a clinical trial. Citation Format: Ariane Morel, Nicolas Viaud, Cécile Bonnafous, Sylvia Trichard, Alix Joulin-Giet, Samia Mizari, Gwendoline Grondin, Nadia Anceriz, J. Zhang, J. Jarzen, J. Wu, Gwendoline Grondin, Laetitia Cohen-Tannoudji, Yannis Morel, Benjamin Rossi, Carine Paturel, Renaud Buffet, Laurent Gauthier, Nicolai Wagtmann, Mathieu Blery. IPH4301, an antibody targeting MICA and MICB exhibits potent cytotoxic activity and immunomodulatory properties for the treatment of cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1491.

CD39 (ENTPD1) is a cell membrane ectonucleotidase that hydrolyzes extracellular immunoactivating ATP and ADP into AMP, which can be further hydrolyzed by ectonucleotidase CD73 into immunosuppressive adenosine. Within the tumor microenvironment, adenosine accumulation causes immune suppression and dysregulation of immune cell infiltrates resulting in tumor spreading. The role of CD39 expression on both Tregs and on tumor cells in promoting immunosuppression has been demonstrated in several reports. Blockade of CD39 may promote anti-tumor immunity by directly accumulating immunostimulating ATP and indirectly by reducing adenosine accumulation. Here, we describe the discovery and preclinical development of an anti-huCD39 blocking antibody for cancer immunotherapy. Parental anti-huCD39 mouse monoclonal antibody was humanized. The humanized mAb specifically binds huCD39 protein, but not CD39-like proteins. Nanomolar affinities for human CD39 were measured in SPR studies on recombinant CD39 protein and in flow cytometry titration studies on CD39 expressing transfectants and tumor cell lines. The humanized mAb blocked human CD39 ATPase activity in vitro in the nanomolar range, as demonstrated using transfected cells, CD39-expressing tumor cell lines, as well as human PBMC and ex-vivo isolated fresh tumor samples. The humanized mAb cross-reacted on cynomolgus CD39 and blocked ATPase activity on cynomolgus PBMC with similar efficacy as on human PBMC. Finally, treatment with blocking anti-CD39 mAb inhibited tumor growth in vivo in mouse tumor models. Taken together, these data support the clinical development of anti-CD39 neutralizing mAb for cancer immunotherapy. Citation Format: Severine Augier, Ivan Perrot, Cecile Dejou, Rachel Joly, Stephane Delahaye, Helene Rispaud Blanc, Caroline Denis, Laurent Gauthier, Armand Bensussan, Jean-francois Eliaou, Yannis Morel, Nathalie Bonnefoy, Jeremy Bastid, Carine Paturel. Preclinical development of a humanized blocking antibody targeting the CD39 immune checkpoint for cancer immunotherapy. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3222.

Monalizumab (IPH2201) is a novel, first-in-class humanized IgG4 targeting the immune checkpoint receptor NKG2A (Natural Killer Group 2A). NKG2A is expressed as a heterodimer with CD94 on the surface of subsets of cytotoxic lymphocytes: NK (Natural Killer) cells, γδ T cells and tumor infiltrating CD8 T lymphocytes. CD94/NKG2A is an inhibitory receptor that binds to HLA-E (Human Leukocyte Antigen-E) in humans and orthologous Qa-1b in mice. Upon ligand binding, CD94/NKG2A triggers inhibitory signaling that reduces NK and CD8 T cell responses. HLA-E is frequently up-regulated on cancer cells of many solid tumors or hematological malignancies, protecting from killing by NKG2A+ immune cells. By blocking the binding of CD94/NKG2A to HLA-E, monalizumab leads to enhancement of NK and cytotoxic T cell responses. The immune checkpoint receptor programmed cell death 1 (PD-1) is another inhibitory receptor widely upregulated by tumor-infiltrating T lymphocytes (TILs). In many tumor types immune surveillance is hampered by the expression of PD-L1, one of the ligands of PD-1. Blocking the PD-1 pathway has proven efficient as anti-tumor therapy. Nevertheless many patients remain refractory to these therapeutics. Combination treatment with PD-1 blockers and mAb to a second checkpoint receptor, CTLA-4, have proven effective only for some patients, suggesting a need for combining with other checkpoint blockers. The A20 cell line is a mouse B cell lymphoma line that expresses PD-L1, but not Qa-1b. Upon subcutaneous injection into Balb/c mice, A20 formed solid tumors in which PD-L1 expression was retained and where Qa-1b expression was induced. A20 tumor growth was controlled by NK and CD8 T cells. In spite of high expression of PD-1 on many immune infiltrating cells, and high expression of PD-L1 on tumor cells, monotherapy with anti-PD-1 or -PD-L1 mAb resulted in only moderate reduction in tumor growth. Interestingly, more than 50% of A20 tumor infiltrating NK cells and about 10% of CD8 T cells expressed CD94/NKG2A. The NKG2A+ CD8 T cell population also co-expressed PD-1. Qa-1b expression was induced not only on the surface of tumor cells but also on infiltrating immune cells in vivo. Consistent with the hypothesis that Qa-1b protects tumor cells from killing by NKG2A+ effector NK and T cells, treatment with an antibody that blocks NKG2A significantly delayed A20 tumor growth. Mice were then treated with both anti-NKG2A and anti-PD-1 or -PD-L1 in combination. These combinations resulted in significantly higher anti-tumor responses compared to monotherapies, characterized by an increased frequency of complete tumor cell regression. Together, these data indicate that blocking NKG2A in conjunction with PD-1/PD-L1 checkpoint inhibitors could provide synergistic anti-tumor efficacy and support the rationale for investigating this combination in clinical trials. Citation Format: Caroline Sola, Thomas Arnoux, Fabien Chanuc, Nicolas Fuseri, Benjamin Rossi, Laurent Gauthier, Corinne Leget, Cécile Bonnafous, Nicolai Wagtmann, Yannis Morel, Pascale André. NKG2A immune checkpoint blockade enhances the anti-tumor efficacy of PD1/PD-L1 inhibitors in a preclinical model. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2342.

CD73 (NT5E) is a cell membrane ectoenzyme of the NTPDase family that plays a major role in the conversion of AMP into Adenosine (Ado). Within the tumor microenvironment, accumulation of Ado causes immune suppression and dysregulation of immune cell infiltrates resulting in tumor spreading. CD73 expression in the tumor environment has been associated with poor disease outcome and/or with a pro-metastatic phenotype. Thus, targeting CD73 may promote anti-tumor immunity by reducing Ado accumulation and may block tumor cell metastasis by inhibiting CD73 on tumor cells. Here, we describe the generation and characterization of novel anti-human CD73 antibodies, intended for the treatment of a wide range of cancers. The research leading to these results has received funding from the European Community's Seventh Framework Program (FP7/2007-2013) under grant agreement n°602200. Antibodies were discovered that inhibited CD73 function by different mechanisms, including the direct blocking of CD73 enzymatic activity or the down-modulation of membrane CD73 expression. Epitope mapping revealed that antibodies acting by these different modes of action bound to distinct sites on CD73. All selected antibodies cross-react with cynomolgus CD73 protein and have strong avidity and affinity for membrane or recombinant CD73, by flow cytometry and Surface Plasmon Resonance, respectively. Antibodies that inhibit CD73 enzymatic activity strongly reduce AMP catabolism by both recombinant and cellular CD73 with IC50 in the nanomolar range. They also efficiently reverse ATP- and AMP-mediated T cell suppression in in vitro assays in presence of both CD39+ and CD73+ cells. The antibodies that induce down-modulation of cellular CD73 expression do not block recombinant CD73 enzyme activity and partially inhibit cellular CD73 activity; they reverse ATP- but not AMP-dependent T cell suppression. The antibodies displaying the most interesting features were humanized. Evaluation of their activity in animal models is ongoing. Citation Format: Marc Giraudon Paoli, Severine Augier, Marilyne Royannez Blemont, Céline Rodriguez, Hélène Rispaud Blanc, Stéphanie Chanteux, Nicolas Gourdin, Laurent Gauthier, Christine Ménétrier Caux, Yannis Morel, Christophe Caux, Carine Paturel, Ivan Perrot. Discovery and characterization of new original blocking antibodies targeting the CD73 immune checkpoint for cancer immunotherapy. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2344.

Background Nasopharyngeal carcinomas (NPC) are consistently associated with the Epstein-Barr virus (EBV). Though NPCs are more radiosensitive and chemosensitive than other tumors of the upper aero-digestive tract, many therapeutic challenges remain. In a previous report, we have presented data supporting a possible therapeutic strategy based on artificial TLR3 stimulation combined to the inhibition of the IAP protein family (Inhibitor of Apoptosis Proteins). The present study was designed to progress towards practical applications of this strategy pursuing 2 main objectives: 1) to formally demonstrate expression of the TLR3 protein by malignant NPC cells; 2) to investigate the effect of poly(A:U) as a novel TLR3-agonist more specific than poly(I:C) which was used in our previous study. Methods TLR3 expression was investigated in a series of NPC cell lines and clinical specimens by Western blot analysis and immunohistochemistry, respectively. The effects on NPC cells growth of the TLR3 ligand poly(A:U) used either alone or in combination with RMT5265, an IAP inhibitor based on Smac-mimicry, were assessed using MTT assays and clonogenic assays. Results TLR3 was detected at a high level in all NPC cell lines and clinical specimens. Low concentrations of poly(A:U) were applied to several types of NPC cells including cells from the C17 xenograft which for the first time have been adapted to permanent propagation in vitro. As a single agent, poly(A:U) had no significant effects on cell growth and cell survival. In contrast, dramatic effects were obtained when it was combined with the IAP inhibitor RMT5265. These effects were obtained using concentrations as low as 0.5 μg/ml (poly(A:U)) and 50 nM (RMT5265). Conclusion These data confirm that TLR3 expression is a factor of vulnerability for NPC cells. They suggest that in some specific pathological and pharmacological contexts, it might be worth to use Smac-mimetics at very low doses, allowing a better management of secondary effects. In light of our observations, combined use of both types of compounds should be considered for treatment of nasopharyngeal carcinomas.

Cross-talk between NK cells and dendritic cells (DCs) is critical for the potent therapeutic response to dsRNA, but the receptors involved remained controversial. We show in this paper that two dsRNAs, polyadenylic-polyuridylic acid and polyinosinic-polycytidylic acid [poly(I:C)], similarly engaged human TLR3, whereas only poly(I:C) triggered human RIG-I and MDA5. Both dsRNA enhanced NK cell activation within PBMCs but only poly(I:C) induced IFN-γ. Although myeloid DCs (mDCs) were required for NK cell activation, induction of cytolytic potential and IFN-γ production did not require contact with mDCs but was dependent on type I IFN and IL-12, respectively. Poly(I:C) but not polyadenylic-polyuridylic acid synergized with mDC-derived IL-12 for IFN-γ production by acting directly on NK cells. Finally, the requirement of both TLR3 and Rig-like receptor (RLR) on mDCs and RLRs but not TLR3 on NK cells for IFN-γ production was demonstrated using TLR3- and Cardif-deficient mice and human RIG-I–specific activator. Thus, we report the requirement of cotriggering TLR3 and RLR on mDCs and RLRs on NK cells for a pathogen product to induce potent innate cell activation.

Background: There is increasing evidence that the toll-like receptor 3 (TLR3) is an interesting target for anti-cancer therapy. Unfortunately, most laboratory investigations about the impact of TLR3 stimulation on human malignant cells have been performed with very high concentrations - 5 to 100 μg/ml - of the prototype TLR3 ligand, poly(I:C). In a previous study focused on a specific type of human carcinoma - nasopharyngeal carcinoma - we have shown that concentrations of poly(I:C) as low as 100 ng/ml are sufficient to induce apoptosis of malignant cells when combined to a pharmacological antagonist of the IAP family based on Smac mimicry.Methods: This observation prompted us to investigate the contribution of the IAP family in cell response to poly(I:C) in a variety of human malignant cell types.Results: We report a rapid, intense and selective increase in c-IAP2 protein expression observed under stimulation by poly(I:C)(500 ng/ml) in all types of human malignant cells. In most cell types, this change in protein expression is underlain by an increase in c-IAP2 transcripts and dependent on the TLR3/TRIF pathway. When poly(I:C) is combined to the IAP inhibitor RMT 5265, a cooperative effect in apoptosis induction and/or inhibition of clonogenic growth is obtained in a large fraction of carcinoma and melanoma cell lines.Conclusions: Currently, IAP inhibitors like RMT 5265 and poly(I:C) are the subject of separate therapeutic trials. In light of our observations, combined use of both types of compounds should be considered for treatment of human malignancies including carcinomas and melanomas. © 2010 Friboulet et al; licensee BioMed Central Ltd., published_or_final_version

There is a high demand for the development of adjuvants that induce cytotoxic T lymphocytes, which are crucial for the elimination of intracellular pathogens and tumor cells. Toll-like receptor (TLR) agonists are prime candidates to fulfill this role because they induce innate immune activation and promote adaptive immune responses. The successful application of the TLR7 agonist R837 for treatment of basal cell carcinoma shows the potential for exploiting this pathway in tumor immunotherapy. Imidazoquinolines like R837 and stimulatory ssRNA oligonucleotides both trigger TLR7-mediated immune activation, but little is known about their comparative ability to promote immunity induction. We investigated differences in innate immune activation and adjuvant activity between the imidazoquinoline R848 and the ssRNA TLR7 agonist polyUs21. In contrast to R848, polyUs21 induced detectable levels of intracellular interferon-α (IFN-α) in plasmacytoid dendritic cells (PDCs). In immunization studies, only polyUs21 led to robust priming of type 1 T helper cells and cytotoxic T lymphocytes, and it was more efficient in inducing antitumor immunity than R848. Notably, exogenous IFN-α augmented the adjuvant activity of R848, whereas depletion of PDC abrogated the adjuvanticity of polyUs21. This study, therefore, identifies sufficient IFN-α production by PDC as an important determinant of vaccine efficacy.

Tumor cells that express reduced levels of Major Histocompatibility Complex (MHC) class I molecules may be recognized and killed by Natural Killer cells (NK cells), through a process known as “missing self” recognition. In humans, this is controlled by inhibitory receptors such as Killer Immunoglobulin-like Receptors (KIR) that recognize Human Leukocyte Antigen (HLA)-A, -B or –C. Engagement of KIR by HLA molecules results in inhibitory signaling that reduces NK cell-mediated natural killing and antibody-dependent cellular cytotoxicity (ADCC). Hence, antibodies that block interactions between inhibitory KIR and their HLA ligands are being evaluated as an anti-cancer therapeutic strategy. The anti-KIR2DL1/2/3-specific monoclonal antibody, lirilumab (BMS-986015 / IPH2102), is a fully human IgG4 that blocks binding of KIR to HLA-C, and is being developed for treating hematologic malignancies and solid tumors. Elotuzumab (BMS901608 / HuLuc63) is a humanized IgG1 anti-SLAMF7 (signaling lymphocyte activation molecule family member 7, CS-1) being developed for the treatment of Multiple Myeloma (MM). SLAMF7 is a cell surface glycoprotein highly expressed in myelomatous cells and only at low levels on normal cells. NK cell-mediated ADCC is one of the main mechanisms of action of elotuzumab, but ADCC is negatively regulated by KIR checkpoint receptors. Thus a combination of lirilumab and elotuzumab has strong scientific rationale. The aim of the present study was to assess whether lirilumab would enhance elotuzumab anti-MM activity in vitro with human peripheral blood NK cells and MM cell lines, and in vivo in a newly developed xenogenic mouse model. Two MM cell lines (OPM-2 and U266B1) were identified that express both HLA-C and SLAMF7. These MM cells were capable of activating peripheral blood NK cells from healthy donors in vitro, as assessed by three different endpoints (CD107 mobilization on NK cells surface and intracellular production of the cytokines IFN-g and TNF- a); each of these responses were significantly enhanced, in a dose-dependent manner, by both lirilumab and elotuzumab independently. Moreover, the elotuzumab-mediated functional activation of KIR2D+ NK cells could be further enhanced by the addition of increasing doses of lirilumab. The best combinatorial effect was observed in response to MM cells expressing low densities of SLAMF7. These data suggest that lirilumab treatment may increase the therapeutic efficacy of elotuzumab, particularly in MM patients with low SLAMF7 expression. In these experiments, it was not possible to clearly identify the impact of Fc receptor genotype or HLA-C genotype on the NK cell responses. To assess the therapeutic efficacy of lirilumab and elotuzumab in vivo, we generated a novel strain of double-transgenic mice expressing human KIR2DL3 as well as its ligand, HLA-cw3, on a Rag1-/- background (KIR-cw3-tgRAG mice), to allow engraftment of human MM tumor cells expressing SLAMF7. The OPM-2 MM cell line was subcutaneously engrafted in these mice and when high tumor volumes were reached, mice were treated with lirilumab, elotuzumab or a combination of both. As monotherapy, each of monoclonal antibody had some therapeutic effect while the combination of both resulted in a significantly stronger anti-tumor effect and increased survival of the mice. Median survival of mice treated with huIgG control was 38 days, 41 days with lirilumab, 42 days with elotuzumab and 51 days with both mAbs in combination (10 mice per group). In conclusion, we demonstrate that blockade of KIR checkpoint receptors with lirilumab was able to augment elotuzumab mediated ADCC in vitro and synergized with elotuzumab to mediate potent anti-MM activity in vivo. Taken together, these data provide a rationale for clinical trials to test combination treatment of lirilumab and elotuzumab in MM patients. Disclosures Sola: InnatePharma: Employment, Equity Ownership. Blery:Innate Pharma: Employment, Equity Ownership. Bonnafous:Innate Pharma: Employment, Equity Ownership. Bonnet:Innate Pharma: Employment, Equity Ownership. Fuseri:Innate Pharma: Employment, Equity Ownership. Graziano:Bristol-Myers Squibb: Employment; Bristol-Myers Squibb: Equity Ownership. Morel:Innate Pharma: Employment, Equity Ownership. André:Innate Pharma: Employment, Equity Ownership.

MICA and MICB, along with ULPBs, are ligands for the activating receptor NKG2D expressed on NK cells and subsets of T cells in Human. NKG2D ligands are induced by cellular stress and pathogen infections. Their expression is tightly regulated by complex mechanisms both at the mRNA and protein levels. In the case of MICA and MICB, more than 65 and 30 alleles respectively were described with different properties regarding to their cellular location adding to the complexity of this recognition system. Nevertheless, as markers of cellular stress, in particular in tumorigenesis, MICA and the closely related MICB proteins are candidates of choice to be targeted by a cytotoxic therapeutic antibody. We first evaluated MICA/B expression by immunohistochemistry on healthy tissues and tumors to validate these antigens as therapeutic targets. Then, using mouse immunization, we generated a panel of chimeric human IgG1 monoclonal antibodies targeting MICA and MICB. These mAbs have the ability to bind to several structurally different alleles and to cross-react on MIC proteins from cynomolgus macaques. Their capacity to block the MICA/NKG2D interaction was assessed by surface plasmon resonance as well as by using cell-based assays. In vitro efficacy was measured by the capacity to mediate complement-dependent cytotoxicity (CDC) and antibody-dependent cell cytotoxicity (ADCC) towards MICA expressing cells. In vivo efficacy of the anti-MICA mAbs was measured in both a preventive and a curative setting using MICA expressing cell lines. Altogether, we have generated a panel of anti-MICA mAbs with diverse functional properties. Ongoing work aims to choose the best candidate for humanization and further clinical development. Citation Format: Mathieu Blery, Cécile Bonnafous, Valentine Peri, Sylvia Trichard, Ivan Perrot, Stéphanie Cornen, Ariane Thielens, Violette Breso, Yannis Morel, François Romagne, Benjamin Rossi, Carine Paturel, Laurent Gauthier. Targeting MICA with therapeutic antibodies for the treatment of cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 5037. doi:10.1158/1538-7445.AM2014-5037

LIGHT is a recently identified member of the TNF superfamily that is up-regulated upon activation of T cells. Herpesvirus entry mediator, one of its receptors, is constitutively expressed on immature dendritic cells (DCs). In this report, we demonstrate that LIGHT induces partial DC maturation as demonstrated by Ag presentation and up-regulation of adhesion and costimulatory molecules. LIGHT-stimulated DCs show reduced macropinocytosis and enhanced allogeneic stimulatory capacity but fail to produce significant amounts of IL-12, IL-6, IL-1β, or TNF-α compared with unstimulated DCs. However, LIGHT cooperates with CD154 (CD40 ligand) in DC maturation, with particular potentiation of allogeneic T cell proliferation and cytokine secretion of IL-12, IL-6, and TNF-α. Moreover, LIGHT costimulation allows DCs to prime in vitro-enhanced specific CTL responses. Our results suggest that LIGHT plays an important role in DC-mediated immune responses by regulating CD154 signals and represents a potential tool for DC-based cancer immunotherapy.

The TNF receptor (TNFR) family plays a central role in the development of the immune response. Here we describe the reciprocal regulation of the recently identified TNFR superfamily member herpes virus entry mediator (HVEM) (TR2) and its ligand LIGHT (TL4) on T cells following activation and the mechanism of this process. T cell activation resulted in down-regulation of HVEM and up-regulation of LIGHT, which were both more pronounced in CD8+ than CD4+ T lymphocytes. The analysis of HVEM and LIGHT mRNA showed an increase in the steady state level of both mRNAs following stimulation. LIGHT, which was present in cytoplasm of resting T cells, was induced both in cytoplasm and at the cell surface. For HVEM, activation resulted in cellular redistribution, with its disappearance from cell surface. HVEM down-regulation did not rely on de novo protein synthesis, in contrast to the partial dependence of LIGHT induction. Matrix metalloproteinase inhibitors did not modify HVEM expression, but did enhance LIGHT accumulation at the cell surface. However, HVEM down-regulation was partially blocked by a neutralizing mAb to LIGHT or an HVEM-Fc fusion protein during activation. As a model, we propose that following stimulation, membrane or secreted LIGHT binds to HVEM and induces receptor down-regulation. Degradation or release of LIGHT by matrix metalloproteinases then contributes to the return to baseline levels for both LIGHT and HVEM. These results reveal a self-regulating ligand/receptor system that contributes to T cell activation through the interaction of T cells with each other and probably with other cells of the immune system.

MICA and MICB, along with ULPBs, are ligands for the activating receptor NKG2D expressed on NK cells and subsets of T cells in Human. NKG2D ligands are induced by cellular stress and pathogen infections. Their expression is tightly regulated by complex mechanisms both at the mRNA and protein levels. In the case of MICA and MICB, more than 65 and 30 alleles respectively were described with different properties regarding to their cellular location adding to the complexity of this recognition system. Nevertheless, as markers of cellular stress, in particular in tumorigenesis, MICA and the closely related MICB proteins are candidates of choice to be targeted by a cytotoxic therapeutic antibody. We first evaluated MICA/B expression by immunohistochemistry on healthy tissues and tumors to validate these antigens as therapeutic targets. Then, using mouse immunization, we generated a panel of chimeric human IgG1 monoclonal antibodies targeting MICA and MICB. These mAbs have the ability to bind to several structurally different alleles and to cross-react on MIC proteins from cynomolgus macaques. Their capacity to block the MICA/NKG2D interaction was assessed by surface plasmon resonance as well as by using cell-based assays. In vitro efficacy was measured by the capacity to mediate complement-dependent cytotoxicity (CDC) and antibody-dependent cell cytotoxicity (ADCC) towards MICA expressing cells. In vivo efficacy of the anti-MICA mAbs was measured in both a preventive and a curative setting using MICA expressing cell lines. Altogether, we have generated a panel of anti-MICA mAbs with diverse functional properties. Ongoing work aims to choose the best candidate for humanization and further clinical development.

Meeting abstracts Natural Killer cells (NK cells) are lymphocytes able to recognize and kill tumors for which the expression of Major Histocompatibility Complex (MHC) class I molecules is altered. This “missing self” recognition is mediated in humans by the lack of engagement of MHC class I i.e