Targeting a membrane-proximal epitope on mesothelin increases the tumoricidal activity of a bispecific antibody blocking CD47 on mesothelin-positive tumors

Mesothelin (MSLN) is a cell surface glycoprotein overexpressed in several solid malignancies, including gastric, lung, mesothelioma, pancreatic and ovarian cancers. While several MSLN-targeting therapeutic approaches are in development, only limited efficacy has been achieved in patients. A potential shortcoming of several described antibody-based approaches is that they target the membrane distal region of MSLN and, additionally, are known to be handicapped by the high levels of circulating soluble MSLN in patients. We show here, using monoclonal antibodies (mAbs) targeting different MSLN-spanning epitopes, that the membrane-proximal region resulted in more efficient killing of MSLN-positive tumor cells in antibody-dependent cell-mediated cytotoxicity (ADCC) assays. Surprisingly, no augmented killing was observed in antibody-dependent cellular phagocytosis (ADCP) by mAbs targeting this membrane-proximal region. To further increase the ADCP potential, we, therefore, generated bispecific antibodies (bsAbs) coupling a high-affinity MSLN binding arm to a blocking CD47 arm. Here, targeting the membrane-proximal domain of MSLN demonstrated enhanced ADCP activity compared to membrane-distal domains when the bsAbs were used in in vitro phagocytosis killing assays. Importantly, the superior anti-tumor activity was also translated in xenograft tumor models. Furthermore, we show that the bsAb approach targeting the membrane-proximal epitope of MSLN optimized ADCC activity by augmenting FcγR-IIIA activation and enhanced ADCP via a more efficient blockade of the CD47/SIRPα axis.

Abstract 546: Selectively targeting CD47 with bispecific antibody to efficiently eliminate mesothelin-positive solid tumors

The CD47- signal regulatory protein α (SIRPα) axis, originally discovered as a mechanism of self-recognition, has emerged as a novel innate immune check-point employed by cancer cells to escape immune surveillance. Over-expression of CD47 on a plethora of hematologic and solid cancers has been shown to be associated with poor prognosis. CD47 blockade is thus considered as an attractive strategy to retune the host immune system toward eliminating cancer cells. Clinical efficacy has been achieved in patients with Non-Hodgkin lymphoma (NHL) treated with a combination of the anti-CD20 monoclonal antibody (mAb), rituximab, and the anti-CD47 mAb, Hu5F9-G4. However, in parallel, due to the ubiquitous expression of CD47 on healthy cells, toxicity is observed limiting exposure which impairs clinical development of anti-CD47 mAbs.

To harness the tumoricidal potential and avoid the liabilities of CD47 blockade, we have developed bispecific antibodies (bsAbs), co-targeting CD47 and a tumor associated antigen (TAA), for selective blockade of CD47 on malignant cells. Mesothelin (MSLN) has been selected as one of these TAAs as it is over-expressed on multiple types of solid tumors. An anti-CD47xMSLN bsAb with a fully functional IgG1 Fc domain has been generated and tested for efficacy and safety in vitro and in vivo using cell-based assays and animal models.

With a panel of human MSLN+ target cells, the bsAb kills more efficiently through Ab-dependent cellular phagocytosis (ADCP) and cell-mediated cytotoxicity (ADCC) as compared to the anti-MSLN mAb, amatuximab. Efficacy of the bsAb was minimally affected by soluble MSLN as compared to amatuximab. Mechanistic studies demonstrated that the increased ADCP and ADCC were due to co-engagement-mediated blockade of both target proteins. In vivo using xenograft models, whereas amatuximab was unable, the bsAb inhibited tumor growth of OVCAR3 and MSLN-transfected HepG2 cell lines. Phenotypic analysis showed that treatment with the bsAb induced the accumulation of myeloid cells with increased F4/80 expression in the tumor microenvironment. Importantly, the bsAb was well-tolerated in an exploratory four-week repeated dose study at the highest dose tested (10 mg/kg) in cynomolgus monkeys.

Conclusion: Selective CD47 targeting on tumor cells with an anti-CD47xMSLN bsAb showed efficient killing of MSLN+ tumor cells in vitro and in vivo. A study in non-human primates administered weekly a therapeutically relevant dose over 28 days was well tolerated demonstrating no adverse hematological profiles.

Citation Format: Limin Shang, Vanessa Buatois, Eric Hatterer, Xavier Chauchet, Hasnaà Haddouk, Stefano Majocchi, Krzysztof Masternak, Marie H. Kosco-Vilbois, Nicolas Fischer, Walter G. Ferlin. Selectively targeting CD47 with bispecific antibody to efficiently eliminate mesothelin-positive solid tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 546.

Abstract A088: Selective blockage of the innate immune checkpoint receptor CD47 on mesothelin (MSLN) positive solid tumor cells via dual targeting bispecific antibodies alters the tumor microenvironment to control tumor growth

Up-regulation of CD47 is an immune evasion mechanism used by different cancers to evade immune surveillance. Through its interaction with signal-regulatory protein alpha (SIRPα) on myeloid cells, CD47 delivers a universal “don’t eat me” signal to phagocytes, which prevents immune cells from efficiently eliminating tumor cells. Blockade of the SIRPα–CD47 innate immune checkpoint has therefore emerged as a new way to treat cancer. Several CD47-targeting molecules are in development with encouraging results obtained with monoclonal antibodies (mAb). However, the pharmacologic properties and the safety profile of molecules indiscriminately blocking CD47 can be improved by selectively inhibiting CD47 only on tumor cells. For this purpose, we generated bispecific antibodies (bsAbs) capable of targeting blockade of CD47 specifically to malignanT-cells through the co-engagement of a tumor-associated antigen (TAA). The bsAb NI-1801 specifically targets mesothelin (MSLN)-positive tumors. NI-1801 was shown to bind to MSLN-positive tumor cells, but not to MSLN-negative cells expressing physiologic levels of CD47 (e.g., leukocytes, erythrocytes, platelets). NI-1801 blocks the CD47-SIRPα interaction in a MSLN-dependent manner and thus minimizes the side effects related to a nonspecific blockade of CD47 on healthy cells. Studying antibody-dependent cellular phagocytosis (ADCP) and antibody-dependent cellular cytotoxicity (ADCC) of various MSLN-positive human tumor cell lines revealed that NI-1801 markedly enhanced killing as compared to amatuximab (an anti-MSLN mAb in clinical trials) and to the corresponding anti-MSLN mAb, exemplifying the role of blocking the “don’t eat me” signal to target cancer. NI-1801 also showed efficacy in various xenograft tumor models and analysis of the tumor microenvironment (TME) revealed a significant increase in leukocyte subpopulations (macrophages/monocytes and NK cells) of NI-1801 treated mice, suggesting that NI-1801 mediates the recruitment of monocytes from blood. Additionally, NI-1801 treatment affected the ratio between MHC-II-low and MHC-II-high macrophages in the TME. Finally, nonhuman primate studies with NI-1801 demonstrated a linear elimination profile, minimal target-mediated drug disposition and no hematologic toxicity. Taken together, these results illustrate that this strategy possesses potent anticancer activities both in vitro and in vivo in conjunction with favorable pharmacologic and toxicologic profiles.

Citation Format: Stefano Majocchi, Valéry Moine, Xavier Chauchet, Lucile Broyer, Laura Cons, Laurence Chatel, Eric Hatterer, Vanessa Buatois, Hasnaà Haddouk, Gérard Didelot, Giovanni Magistrelli, Yves Poitevin, Ulla Ravn, Anne Papaioannou, Françoise Richard, Limin Shang, Marie H. Kosco-Vilbois, Nicolas Fischer, Walter G. Ferlin, Krzysztof Masternak. Selective blockage of the innate immune checkpoint receptor CD47 on mesothelin (MSLN) positive solid tumor cells via dual targeting bispecific antibodies alters the tumor microenvironment to control tumor growth [abstract]. In: Proceedings of the Fourth CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; Sept 30-Oct 3, 2018; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2019;7(2 Suppl):Abstract nr A088.

Co-engaging CD47 and CD19 with a bispecific antibody abrogates B-cell receptor/CD19 association leading to impaired B-cell proliferation

CD19 is a B cell-specific receptor that regulates the threshold of B cell receptor (BCR)-mediated cell proliferation. A CD47xCD19 bispecific antibody (biAb) was generated to target and deplete B cells via multiple antibody-mediated mechanisms. Interestingly, the biAb, constructed of a CD19 binding arm and a CD47 binding arm, inhibited BCR-mediated B-cell proliferation with an effect even more potent than a CD19 monoclonal antibody (mAb). The inhibitory effect of the biAb was not attributable to CD47 binding because a monovalent or bivalent anti-CD47 mAb had no effect on B cell proliferation. Fluorescence resonance energy transfer analysis demonstrated that co-engaging CD19 and CD47 prevented CD19 clustering and its migration to BCR clusters, while only engaging CD19 (with a mAb) showed no impact on either CD19 clustering or migration. The lack of association between CD19 and the BCR resulted in decreased phosphorylation of CD19 upon BCR activation. Furthermore, the biAb differentially modulated BCR-induced gene expression compared to a CD19 mAb. Taken together, this unexpected role of CD47xCD19 co-ligation in inhibiting B cell proliferation illuminates a novel approach in which two B cell surface molecules can be tethered, to one another in order, which may provide a therapeutic benefit in settings of autoimmunity and B cell malignancies.

Abstract 2770: Dual-targeting mesothelin/CD47 bispecific antibodies for tumor-directed blockade of CD47 in solid cancer

Mesothelin (MSLN) is a lineage restricted cell surface protein with unknown biological function, expressed at low levels on mesothelial cells in healthy tissue. MSLN is also a tumor differentiation antigen as it is highly expressed across a wide range of solid tumors with the highest prevalence in mesothelioma, pancreatic, biliary, ovarian, lung and gastric cancers. Most solid and hematological cancers also upregulate the expression of CD47, a ubiquitous innate immune checkpoint receptor. CD47 interacts with signal-regulatory protein alpha (SIRPα) on myeloid cells, which leads to the inhibition of tumor cell phagocytosis and anti-tumor immune responses. Accordingly, elevated levels of CD47 on tumor cells are associated with cancer's immune evasion capacity and correlate with poor clinical prognosis, all of which makes CD47 a relevant target for therapeutic blockade. We generated a series of dual-targeting bispecific CD47/MSLN antibodies (biAbs) selectively binding to MSLN-positive tumor cells, but not MSLN-negative healthy cells expressing physiological levels of CD47 (e.g., all blood cells). These CD47/MSLN biAbs block CD47-SIRPα interaction in a MSLN-dependent, tumor-specific manner, thus permitting to bypass tolerability and “antigen sink” issues related to ubiquitous CD47 expression in healthy tissues. An array of CD47/MSLN biAbs with anti-MSLN arms targeting different MSLN epitopes was tested in vitro, in antibody dependent cellular phagocytosis (ADCP) and antibody dependent cellular cytotoxicity (ADCC) assays, as well as for anti-tumor activity in vivo using mouse xenograft models. With various MSLN-positive human cancer cell lines, MSLN/CD47 biAbs demonstrate significantly enhanced cancer cell killing by ADCC and ADCP as compared to the corresponding anti-MSLN monoclonal antibody format (mAbs) as well as to amatuximab, a therapeutic anti-MSLN mAb (currently in Phase II clinical trials for mesothelioma). Correspondingly, the MSLN/CD47 biAbs also display superior efficacy in controlling tumor growth in the xenograft models in vivo. Taken together, we conclude that MSLN/CD47 biAbs should allow for efficacious, yet safe, targeting of CD47 in multiple solid tumor indications in the clinic. More generally, our data support the concept of tumor-directed blockade of CD47 with biAbs as a novel way of improving the efficacy of antibody-based cancer therapies.

Citation Format: Valéry Moine, Lucile Broyer, Xavier Chauchet, Eric Hatterer, Stefano Majocchi, Vanessa Buatois, Limin Shang, Gérard Didelot, Giovanni Magistrelli, Yves Poitevin, Ulla Ravn, Marie H. Kosco-Vilbois, Nicolas Fiischer, Walter G. Ferlin, Krzysztof Masternak. Dual-targeting mesothelin/CD47 bispecific antibodies for tumor-directed blockade of CD47 in solid cancer [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 2770.

Preclinical Development of a Bispecific Antibody that Safely and Effectively Targets CD19 and CD47 for the Treatment of B-Cell Lymphoma and Leukemia

CD47, an ubiquitously expressed innate immune checkpoint receptor that serves as a universal "don't eat me" signal of phagocytosis, is often upregulated by hematologic and solid cancers to evade immune surveillance. Development of CD47-targeted modalities is hindered by the ubiquitous expression of the target, often leading to rapid drug elimination and hemotoxicity including anemia. To overcome such liabilities, we have developed a fully human bispecific antibody, NI-1701, designed to coengage CD47 and CD19 selectively on B cells. NI-1701 demonstrates favorable elimination kinetics with no deleterious effects seen on hematologic parameters following single or multiple administrations to nonhuman primates. Potent in vitro and in vivo activity is induced by NI-1701 to kill cancer cells across a plethora of B-cell malignancies and control tumor growth in xenograft mouse models. The mechanism affording maximal tumor growth inhibition by NI-1701 is dependent on the coengagement of CD47/CD19 on B cells inducing potent antibody-dependent cellular phagocytosis of the targeted cells. NI-1701-induced control of tumor growth in immunodeficient NOD/SCID mice was more effective than that achieved with the anti-CD20 targeted antibody, rituximab. Interestingly, a synergistic effect was seen when tumor-implanted mice were coadministered NI-1701 and rituximab leading to significantly improved tumor growth inhibition and regression in some animals. We describe herein, a novel bispecific antibody approach aimed at sensitizing B cells to become more readily phagocytosed and eliminated thus offering an alternative or adjunct therapeutic option to patients with B-cell malignancies refractory/resistant to anti-CD20-targeted therapy. Mol Cancer Ther; 17(8); 1739-51. ©2018 AACR.

A specific anti-citrullinated protein antibody profile identifies a group of rheumatoid arthritis patients with a toll-like receptor 4-mediated disease

BACKGROUND

Increased expression of toll-like receptor 4 (TLR4) and its endogenous ligands, is characteristic of rheumatoid arthritis (RA) synovitis. In this study, we evaluated how these TLR4 ligands may drive pathogenic processes and whether the fine profiling of anti-citrullinated protein antibodies (ACPA) based on their target specificity might provide a simple means to predict therapeutic benefit when neutralizing TLR4 in this disease.

METHODS

The capacity of RA synovial fluids (RASF) to stimulate cytokine production in monocytes from patients with RA was analyzed by ELISA. The presence of TLR4 activators in RASF was determined by measuring the levels of ACPA, ACPA subtypes with reactivity to specific citrullinated peptides and other TLR4 ligands. Neutralization of TLR4 signaling was investigated using NI-0101, a therapeutic antibody that targets TLR4.

RESULTS

RASF exhibited a heterogeneous capacity to induce production of proinflammatory cytokines by monocytes isolated from patients with RA. Such cytokine responses were significantly modified by TLR4 blockade achieved using NI-0101. The analysis of the content of RASF and matched sera demonstrated that ACPA fine specificities in patient samples predict cellular response to anti-TLR4 exposure in vitro.

CONCLUSION

TLR4 represents a possible therapeutic target in RA. Our study demonstrates that TLR4 inhibition in an ex vivo model of RA pathogenesis can significantly modulate cytokine release and does so in specific subgroups of RA patient-derived samples. It also suggests that ACPA fine profiling has the potential to identify RA patients with a predominantly TLR4-driven pathotype that could be used to predict preferential response to TLR4 antagonism.

Spatiotemporal expression of endogenous TLR4 ligands leads to inflammation and bone erosion in mouse collagen-induced arthritis

Increased expression of endogenous Toll-like receptor 4 (TLR4) ligands (e.g., Tenascin-C, S100A8/A9, citrullinated fibrinogen (cFb) immune complexes) has been observed in patients with rheumatoid arthritis (RA). However, their roles in RA pathogenesis are not well understood. Here, we investigated the expression kinetics and role of endogenous TLR4 ligands in the murine model of collagen-induced arthritis (CIA). Tenascin-C was upregulated in blood early in CIA, and correlated positively with the clinical score at day 56. Levels of S100A8/A9 increased starting from day 28, peaking at day 42, and correlated positively with joint inflammation. Levels of anti-cFb antibodies increased during the late phase of CIA and correlated positively with both joint inflammation and cartilage damage. Blockade of TLR4 activation at the time of the first TLR4 ligand upregulation prevented clinical and histological signs of arthritis. A TLR4-dependent role was also observed for Tenascin-C and cFb immune complexes in osteoclast differentiation in vitro. Taken together, our data suggests that the pathogenic contribution of TLR4 in promoting joint inflammation and bone erosion during CIA occurs via various TLR4 ligands arising at different stages of disease. The data also suggests that Blockade of TLR4 with monoclonal antibodies is a promising strategy in RA treatment.

Abstract 1495: Neutralization of CD47 in cancer cells with bispecific antibodies harnesses the phagocytic potential of tumor-infiltrating macrophages

The inhibitory “don't eat me” signal of phagocytosis, CD47, is commonly overexpressed in cancer cells, a feature generally associated with poor prognosis. CD47 overexpression in cancer is believed to promote immune evasion by allowing tumor cells to “hide” from innate immune phagocytes like macrophages or dendritic cells. CD47 is therefore a new type of immune checkpoint and an attractive target for cancer immunotherapy. However, as CD47 is also universally expressed on healthy cells, clinical development of anti-CD47 monoclonal antibodies is inevitably limited by toxicity and/or pharmacokinetic issues. To overcome these liabilities, we engineered dual-targeting bispecific antibodies (biAbs) for selective blockade of CD47 in malignant cells. By tethering the biAbs strongly to cells expressing a tumor-associated antigen (TAA), such as CD19 or mesothelin, CD47 is blocked selectively on the target cell. In contrast, as these biAbs will lose the avidity effect with TAA-negative cells, they will bind with very low affinity to healthy cells which express CD47. In this manner, dual-targeting should help to sidestep safety and pharmacokinetic “sink” problems resulting from ubiquitous CD47 expression. Studies in non-human primates performed with the CD47/CD19 therapeutic candidate NI-1701 confirmed this prediction, demonstrating normal IgG1 pharmacokinetics and absence of toxicity, even at high antibody doses (100 mg/kg per week).

Hence, the mechanism of action of CD47/TAA dual-targeting antibodies is heavily contingent upon target co-engagement. In vitro, CD19-positive or mesothelin-positive cancer cells are efficiently killed through antibody dependent cellular phagocytosis (ADCP) and/or antibody-dependent cell-mediated cytotoxicity (ADCC) in the presence of effector cells, such as macrophages or natural killer cells, and the corresponding dual-targeting CD47/TAA antibodies. Their enhanced ability to induce tumor cell phagocytosis was also demonstrated in vivo, in xenograft models: Mice implanted with subcutaneous human B cell lymphoma xenografts controlled tumor growth following therapy with NI-1701, contrary to mice treated with an anti-CD19 mAb. Importantly, tumor microenvironment (TME) studies revealed that mouse macrophages infiltrating human tumors engulfed tumor cells more frequently—and at a significantly higher rate—in animals treated with NI-1701 as compared to controls. Moreover, the observed superior phagocytic activity of tumor-infiltrating macrophages was associated with a reduction of granulocytic myeloid-derived suppressor cell infiltrates, suggesting that NI-1701 may favor the establishment of a tumor-hostile, immunostimulatory TME. We conclude that dual-targeting CD47/TAA bispecific antibodies may open the way to the safe and efficacious therapeutic neutralization of CD47, the universal ‘don't eat me’ signal hijacked by cancer cells.

Citation Format: Krzysztof Masternak, Valéry Moine, Lucile Broyer, Xavier Chauchet, Vanessa Buatois, Elie Dheilly, Stefano Majocchi, Giovanni Magistrelli, Yves Poitevin, Ulla Ravn, Eric Hatterer, Susana Salgado Pires, Limin Shang, Zoë Johnson, Walter Ferlin, Marie Kosco-Vilbois, Nicolas Fischer. Neutralization of CD47 in cancer cells with bispecific antibodies harnesses the phagocytic potential of tumor-infiltrating macrophages. [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 1495.

Anti-CD79 antibody induces B cell anergy that protects against autoimmunity

B cells play a major role in the pathogenesis of many autoimmune disorders, including rheumatoid arthritis, systemic lupus erythematosus, multiple sclerosis, and type I diabetes mellitus, as indicated by the efficacy of B cell-targeted therapies in these diseases. Therapeutic effects of the most commonly used B cell-targeted therapy, anti-CD20 mAb, are contingent upon long-term depletion of peripheral B cells. In this article, we describe an alternative approach involving the targeting of CD79, the transducer subunit of the B cell AgR. Unlike anti-CD20 mAbs, the protective effects of CD79-targeted mAbs do not require cell depletion; rather, they act by inducing an anergic-like state. Thus, we describe a novel B cell-targeted approach predicated on the induction of B cell anergy.

Characterization of a surrogate murine antibody to model anti-human CD3 therapies

Fc-modified anti-human CD3ε monoclonal antibodies (mAbs) are in clinical development for the treatment of autoimmune diseases. These next generation mAbs have completed clinical trials in patients with type-1 diabetes and inflammatory bowel disease demonstrating a narrow therapeutic window. Lowered doses are ineffective, yet higher pharmacologically-active doses cause an undesirable level of adverse events. Thus, there is a critical need for a return to bench research to explore ways of improving clinical outcomes. Indeed, we recently reported that a short course of treatment affords synergy, providing long-term disease amelioration when combining anti-mouse CD3 and anti-mouse tumor necrosis factor mAbs in experimental arthritis. Such strategies may widen the window between risk and benefit; however, to more accurately assess experimentally the biology and pharmacology, reagents that mimic the current development candidates were required. Consequently, we engineered an Fc-modified anti-mouse CD3ε mAb, 2C11-Novi. Here, we report the functional characterization of 2C11-Novi demonstrating that it does not bind FcγR in vitro and elicits little cytokine release in vivo, while maintaining classical pharmacodynamic effects (CD3-TCR downregulation and T cell killing). Furthermore, we observed that oral administration of 2C11-Novi ameliorated progression of remitting-relapsing experimental autoimmune encephalitis in mice, significantly reducing the primary acute and subsequent relapse phase of the disease. With innovative approaches validated in two experimental models of human disease, 2C11-Novi represents a meaningful tool to conduct further mechanistic studies aiming at exploiting the immunoregulatory properties of Fc-modified anti-CD3 therapies via combination therapy using parenteral or oral routes of administration.

Syk kinase is phosphorylated in specific areas of the developing nervous system

An increasing number of data involve immunoreceptors in brain development, synaptic plasticity and behavior. However it has yet to be determined whether these proteins in fact transmit an immunoreceptor-like signal in non-hematopoietic neuronal cells. The recruitment and activation of the Syk family tyrosine kinases, Syk and ZAP-70, being a critical step in this process, we conducted a thorough analysis of Syk/ZAP-70 expression pattern in nervous tissues. Syk/ZAP-70 is present in neurons of different structures including the cerebellum, the hippocampus, the visual system and the olfactory system. During the olfactory system ontogeny the protein is detected from the 16th embryonic day and persists in adulthood. Importantly, Syk was phosphorylated on tyrosine residues representative of an active form of the kinase in specialized neuronal subpopulations comprising rostral migratory stream neuronal progenitor cells, hippocampal pyramidal cells, retinal ganglion cells and cerebellar granular cells. Phospho-Syk staining was also observed in synapse-rich regions such as the olfactory bulb glomeruli and the retina inner plexiform layer. Furthermore, our work on cultured primary hippoccampal neurons indicates that as for hematopoietic cells, Syk phosphorylation is readily induced upon pervanadate treatment. Therefore, Syk appears to be a serious candidate in connecting immunoreceptors to downstream adaptor/effector molecules in neurons.

Although IL-6 trans-signaling is sufficient to drive local immune responses, classical IL-6 signaling is obligate for the induction of T cell-mediated autoimmunity

IL-6-mediated T cell-driven immune responses are associated with signaling occurring through the membrane-bound cognate receptor α-chain (mIL-6Rα). Once formed, IL-6-mIL-6Rα complexes induce the homodimerization and subsequent phosphorylation of the ubiquitously expressed signal-transducing protein, gp130. This signaling event is defined as classical IL-6 signaling. However, many inflammatory processes assigned to IL-6 may be mediated via binding a naturally occurring soluble IL-6Rα, which forms an agonistic complex (IL-6/soluble IL-6Rα) capable of evoking responses on a wide range of cell types that lack mIL-6Rα (IL-6 trans-signaling). To dissect the differential contribution of the two IL-6 signaling pathways in cell-mediated inflammatory processes, we pharmaceutically targeted each using two murine models of human arthritis. Whereas intra-articular neutralization of trans-signaling attenuated local inflammatory responses, the classical pathway was found to be obligate and sufficient to induce pathogenic T cells and humoral responses, leading to systemic disease. Our data illustrate that mechanisms occurring in the secondary lymphoid organs underlying arthropathies are mediated via the classical pathway of IL-6 signaling, whereas trans-signaling contributes only at the local site, that is, in the affected tissues.

Cerebrospinal fluid dendritic cells infiltrate the brain parenchyma and target the cervical lymph nodes under neuroinflammatory conditions

Background

In many neuroinflammatory diseases, dendritic cells (DCs) accumulate in several compartments of the central nervous system (CNS), including the cerebrospinal fluid (CSF). Myeloid DCs invading the inflamed CNS are thus thought to play a major role in the initiation and perpetuation of CNS-targeted autoimmune responses. We previously reported that, in normal rats, DCs injected intra-CSF migrated outside the CNS and reached the B-cell zone of cervical lymph nodes. However, there is yet no information on the migratory behavior of CSF-circulating DCs under neuroinflammatory conditions.

Methodology/Principal Findings

To address this issue, we performed in vivo transfer experiments in rats suffering from experimental autoimmune encephalomyelitis (EAE), a model of multiple sclerosis. EAE or control rats were injected intra-CSF with bone marrow-derived myeloid DCs labeled with the fluorescent marker carboxyfluorescein diacetate succinimidyl ester (CFSE). In parallel experiments, fluorescent microspheres were injected intra-CSF to EAE rats in order to track endogenous antigen-presenting cells (APCs). Animals were then sacrificed on day 1 or 8 post-injection and their brain and peripheral lymph nodes were assessed for the presence of microspheres⁺ APCs or CFSE⁺ DCs by immunohistology and/or FACS analysis. Data showed that in EAE rats, DCs injected intra-CSF substantially infiltrated several compartments of the inflamed CNS, including the periventricular demyelinating lesions. We also found that in EAE rats, as compared to controls, a larger number of intra-CSF injected DCs reached the cervical lymph nodes. This migratory behavior was accompanied by an accentuation of EAE clinical signs and an increased systemic antibody response against myelin oligodendrocyte glycoprotein, a major immunogenic myelin antigen.

Conclusions/Significance

Altogether, these results indicate that CSF-circulating DCs are able to both survey the inflamed brain and to reach the cervical lymph nodes. In EAE and maybe multiple sclerosis, CSF-circulating DCs may thus support the immune responses that develop within and outside the inflamed CNS.

The CB(2) cannabinoid receptor controls myeloid progenitor trafficking: involvement in the pathogenesis of an animal model of multiple sclerosis

Cannabinoids are potential agents for the development of therapeutic strategies against multiple sclerosis. Here we analyzed the role of the peripheral CB(2) cannabinoid receptor in the control of myeloid progenitor cell trafficking toward the inflamed spinal cord and their contribution to microglial activation in an animal model of multiple sclerosis (experimental autoimmune encephalomyelitis, EAE). CB(2) receptor knock-out mice showed an exacerbated clinical score of the disease when compared with their wild-type littermates, and this occurred in concert with extended axonal loss, T-lymphocyte (CD4(+)) infiltration, and microglial (CD11b(+)) activation. Immature bone marrow-derived CD34(+) myeloid progenitor cells, which play a role in neuroinflammatory pathologies, were shown to express CB(2) receptors and to be abundantly recruited toward the spinal cords of CB(2) knock-out EAE mice. Bone marrow-derived cell transfer experiments further evidenced the increased contribution of these cells to microglial replenishment in the spinal cords of CB(2)-deficient animals. In line with these observations, selective pharmacological CB(2) activation markedly reduced EAE symptoms, axonal loss, and microglial activation. CB(2) receptor manipulation altered the expression pattern of different chemokines (CCL2, CCL3, CCL5) and their receptors (CCR1, CCR2), thus providing a mechanistic explanation for its role in myeloid progenitor recruitment during neuroinflammation. These findings demonstrate the protective role of CB(2) receptors in EAE pathology; provide evidence for a new site of CB(2) receptor action, namely the targeting of myeloid progenitor trafficking and its contribution to microglial activation; and support the potential use of non-psychoactive CB(2) agonists in therapeutic strategies for multiple sclerosis and other neuroinflammatory disorders.

Bone marrow CD34+/B220+ progenitors target the inflamed brain and display in vitro differentiation potential toward microglia

Recent evidence indicates that microglial cells may not derive from blood circulating mature monocytes as they express features of myeloid progenitors. Here, we observed that a subpopulation of microglial cells expressed CD34 and B220 antigens during brain development. We thus hypothesized that microglia, or a subset of microglial cells, originate from blood circulating CD34+/B220+ myeloid progenitors, which could target the brain under developmental or neuroinflammatory conditions. Using experimental allergic encephalomyelitis (EAE) as a model of chronic neuroinflammation, we found that a discrete population of CD34+/B220+ cells expands in both blood and brain of diseased animals. In EAE mice, intravenous transfer experiments showed that macrophage-colony stimulating factor (M-CSF) -expanded CD34+ myeloid progenitors target the inflamed central nervous system (CNS) while keeping their immature phenotype. Based on these results, we then assessed whether CD34+/B220+ cells display in vitro differentiation potential toward microglia. For this purpose, CD34+/B220+ cells were sorted from M-CSF-stimulated bone marrow (BM) cultures and exposed to a glial cell conditioned medium. Under these experimental conditions, CD34+/B220+ cells were able to differentiate into microglial-like cells showing the morphological and phenotypic features of native microglia. Overall, our data suggest that under developmental or neuroinflammatory conditions, a subpopulation of microglial cells derive from CNS-invading CD34+/B220+ myeloid progenitors.

Rat choroid plexuses contain myeloid progenitors capable of differentiation toward macrophage or dendritic cell phenotypes

The interface between the blood and the cerebrospinal fluid (CSF) is formed by the choroid plexuses (CPs), which are specialized structures located within the brain ventricles. They are composed of a vascularized stroma surrounded by a tight epithelium that controls molecular and cellular traffic between the blood and the CSF. Cells expressing myeloid markers are present within the choroidal stroma. However, the exact identity, maturation state, and functions of these CP-associated myeloid cells are not fully clarified. We show here that this cell population contains immature myeloid progenitors displaying a high proliferative potential. Thus, in neonate rats and, to a lesser extent, in adult rats, cultured CP stroma cells form large colonies of macrophages, in response to M-CSF or GM-CSF, while, under the same conditions, peripheral blood monocytes do not. In addition, under GM-CSF treatment, free-floating colonies of CD11c(+) monocytic cells are generated which, when restimulated with GM-CSF and IL-4, differentiate into OX62(+)/MHC class II(+) dendritic cells. Interestingly, in CP stroma cultures, myeloid cells are found in close association with fibroblastic-like cells expressing the neural stem-cell marker nestin. Similarly, in the developing brain, macrophages and nestin(+) fibroblastic cells accumulate in vivo within the choroidal stroma. Taken together, these results suggest that the CP stroma represents a niche for myeloid progenitors and may serve as a reservoir for brain macrophages.

How to drain without lymphatics? Dendritic cells migrate from the cerebrospinal fluid to the B-cell follicles of cervical lymph nodes

The lack of draining lymphatic vessels in the central nervous system (CNS) contributes to the so-called "CNS immune privilege." However, despite such a unique anatomic feature, dendritic cells (DCs) are able to migrate from the CNS to cervical lymph nodes through a yet unknown pathway. In this report, labeled bone marrow-derived myeloid DCs were injected stereotaxically into the cerebrospinal fluid (CSF) or brain parenchyma of normal rats. We found that DCs injected within brain parenchyma migrate little from their site of injection and do not reach cervical lymph nodes. In contrast, intra-CSF-injected DCs either reach cervical lymph nodes or, for a minority of them, infiltrate the subventricular zone, where neural stem cells reside. Surprisingly, DCs that reach cervical lymph nodes preferentially target B-cell follicles rather than T-cell-rich areas. This report sheds a new light on the specific role exerted by CSF-infiltrating DCs in the control of CNS-targeted immune responses.