Carcinoembryonic antigen-related cell adhesion molecule 1 inhibits proximal TCR signaling by targeting ZAP-70

High-dimensional mapping of human CEACAM1 expression on immune cells and association with melanoma drug resistance

BACKGROUND

Human carcinoembryonic antigen cell adhesion molecule 1 (CEACAM1) is an inhibitory cell surface protein that functions through homophilic and heterophilic ligand binding. Its expression on immune cells in human tumors is poorly understood.

METHODS

An antibody that distinguishes human CEACAM1 from other highly related CEACAM family members was labeled with 159Tb and inserted into a panel of antibodies that included specificity for programmed cell death protein 1 (PD1) and PD-L1, which are targets of immunotherapy, to gain a data-driven immune cell atlas using cytometry by time-of-flight (CyTOF). A detailed inventory of CEACAM1, PD1, and PD-L1 expression on immune cells in metastatic lesions to lymph node or soft tissues and peripheral blood samples from patients with treatment-naive and -resistant melanoma as well as peripheral blood samples from healthy controls was performed.

RESULTS

CEACAM1 is absent or at low levels on healthy circulating immune cells but is increased on immune cells in peripheral blood and tumors of melanoma patients. The majority of circulating PD1-positive NK cells, innate T cells, B cells, monocytic cells, dendritic cells, and CD4+ T cells in the peripheral circulation of treatment-resistant disease co-express CEACAM1 and are demonstrable as discrete populations. CEACAM1 is present on distinct types of cells that are unique to the tumor microenvironment and exhibit expression levels that are highest in treatment resistance; this includes tumor-infiltrating CD8+ T cells.

CONCLUSIONS

To the best of our knowledge, this work represents the first comprehensive atlas of CEACAM1 expression on immune cells in a human tumor and reveals an important correlation with treatment-resistant disease. These studies suggest that agents targeting CEACAM1 may represent appropriate partners for PD1-related pathway therapies.

Cell4D: a general purpose spatial stochastic simulator for cellular pathways

BACKGROUND

With the generation of vast compendia of biological datasets, the challenge is how best to interpret 'omics data alongside biochemical and other small-scale experiments to gain meaningful biological insights. Key to this challenge are computational methods that enable domain-users to generate novel hypotheses that can be used to guide future experiments. Of particular interest are flexible modeling platforms, capable of simulating a diverse range of biological systems with low barriers of adoption to those with limited computational expertise.

RESULTS

We introduce Cell4D, a spatial-temporal modeling platform combining a robust simulation engine with integrated graphics visualization, a model design editor, and an underlying XML data model capable of capturing a variety of cellular functions. Cell4D provides an interactive visualization mode, allowing intuitive feedback on model behavior and exploration of novel hypotheses, together with a non-graphics mode, compatible with high performance cloud compute solutions, to facilitate generation of statistical data. To demonstrate the flexibility and effectiveness of Cell4D, we investigate the dynamics of CEACAM1 localization in T-cell activation. We confirm the importance of Ca2+ microdomains in activating calmodulin and highlight a key role of activated calmodulin on the surface expression of CEACAM1. We further show how lymphocyte-specific protein tyrosine kinase can help regulate this cell surface expression and exploit spatial modeling features of Cell4D to test the hypothesis that lipid rafts regulate clustering of CEACAM1 to promote trans-binding to neighbouring cells.

CONCLUSIONS

Through demonstrating its ability to test and generate hypotheses, Cell4D represents an effective tool to help integrate knowledge across diverse, large and small-scale datasets.

CT109-SN-38, a Novel Antibody-drug Conjugate with Dual Specificity for CEACAM5 and 6, Elicits Potent Killing of Pancreatic Cancer Cells

BACKGROUND

CEACAM5 and CEACAM6 are glycosylphosphatidylinositol (GPI)- linked members of the carcinoembryonic antigen-related cell adhesion molecule (CEACAM) family, which are frequently upregulated in epithelial cancers where they contribute to invasion, metastasis, immune evasion, and resistance to anoikis. CT109 is a novel antibody with dual specificity to both CEACAM5 and 6.

OBJECTIVES

In this study, we aimed to perform the preclinical characterization of CT109 and antibody- drug conjugate (ADCs) derivatives of CT109, focusing on CT109-SN-38.

METHODS

CT109's cognate epitope was characterized by scanning mutagenesis. CT109 specificity and internalization kinetics were assessed by immunoblot and flow cytometry, respectively. Cognate antigen expression prevalence in colorectal cancer and normal tissue arrays was determined by immunohistochemistry. CT109 conjugations were generated by the reaction of reduced CT109 cysteines with maleimide-functionalized payload linkers. In vitro cytotoxic activity of CT109 ADCs was characterized on antigen-positive and negative pancreatic ductal adenocarcinoma cell (PDAC) lines using a luminometric viability assay. In vivo efficacy of CT109-SN-38 was assessed on a PDAC tumor xenograft model at 10 and 25 mg/kg concentrations.

RESULTS

CT109 was shown to bind a glycoepitope centered on N309. CT109 is internalized in the CEACAM5+/CEACAM6+ double-positive PDAC line, BxPC-3, with a t1/2 of 2.3 hours. CT109 ADCs elicit a dose and antigen-dependent cytotoxic effect, with CT109-SN-38 exhibiting an IC50 value of 21 nM in BxPC-3 cells. In a BxPC-3 tumor xenograft model, CT109-SN-38 reduced tumor growth and induced regression in 3/10 mice at a concentration 25 mg/kg.

CONCLUSION

These data suggest that further preclinical and clinical development of CT109-SN-38 is warranted.

Identification of the shared gene signatures and molecular pathways in systemic lupus erythematosus and diffuse large B-cell lymphoma

BACKGROUND

Diffuse large B-cell lymphoma (DLBCL) incidence is higher in systemic lupus erythematosus (SLE) patients than the general population, but the molecular mechanisms behind this link remain ambiguous. The aim of this study was to investigate shared gene signatures and molecular pathways between SLE and DLBCL.

METHODS

We procured expression profiles of SLE and DLBCL from public databases and identified common differentially expressed genes (DEGs). Functional pathway enrichment and protein-protein interaction (PPI) analyses were performed on these shared genes. The molecular complex detection technology (MCODE) and eXtreme Gradient Boosting (XGBoost) machine learning algorithm were used to select core shared genes, followed by Gene Set Enrichment Analysis (GSEA) and immune infiltration analysis.

RESULTS

We identified 54 DEGs as shared genes, among which CD177, CEACAM1, GPR84 and IFIT3 were identified as core shared genes. These genes showed strong associations with inflammatory and immune response pathways. We found a significant positive correlation between GPR84 and IFIT3 expression levels and the immune microenvironment. Decreased expression levels of GPR84 and IFIT3 were linked to enhanced immune therapy sensitivity, potentially due to lower dysregulation scores during low expression. We also discovered that TP53 mutations might elevate CD177 and GPR84 expression and that reduced expression levels of GPR84 and IFIT3 were linked with better overall survival and progression-free survival in DLBCL patients.

CONCLUSIONS

Our study provides valuable insights into the shared molecular mechanisms underpinning the pathogenesis of SLE and DLBCL. These findings could potentially offer new biomarkers and therapeutic targets for SLE and DLBCL.

The role of carcinoembryonic antigen-related cell adhesion molecule 1 in cancer

The Carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1), also known as CD66a, is a member of the immunoglobulin superfamily. CEACAM1 was shown to be a prognostic marker in patients suffering from cancer. In this review, we summarize pre-clinical and clinical evidence linking CEACAM1 to tumorigenicity and cancer progression. Furthermore, we discuss potential CEACAM1-based mechanisms that may affect cancer biology.

CEACAMS 1, 5, and 6 in disease and cancer: interactions with pathogens

The CEA family comprises 18 genes and 11 pseudogenes located at chromosome 19q13.2 and is divided into two main groups: cell surface anchored CEA-related cell adhesion molecules (CEACAMs) and the secreted pregnancy-specific glycoproteins (PSGs). CEACAMs are highly glycosylated cell surface anchored, intracellular, and intercellular signaling molecules with diverse functions, from cell differentiation and transformation to modulating immune responses associated with infection, inflammation, and cancer. In this review, we explore current knowledge surrounding CEACAM1, CEACAM5, and CEACAM6, highlight their pathological significance in the areas of cancer biology, immunology, and inflammatory disease, and describe the utility of murine models in exploring questions related to these proteins.

Activation of CEACAM1 with an agonistic monoclonal antibody results in inhibition of melanoma cells

Inhibitory receptors (IRs), such as the carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1), are cell surface molecules expressed on both normal epithelial, endothelial, and hematopoietic cells and on neoplastic cells. IRs are usually used by cancer cells to inhibit immune cell functions. Thus, CEACAM1 positive tumor cells can interact homophilically with CEACAM1 expressed on T and NK cells to inhibit their antibody-dependent cell-mediated cytotoxicity (ADCC). In this study, we investigated the effect of agonistic/activating anti-CEACAM1 monoclonal antibody (mAb) on melanoma cell lines in vitro and in vivo, following our hypothesis that activation of CEACAM1 on melanoma cells by distinct mAbs may induce inhibition of cancer cell proliferation and/or their death. To address this, we established an activating anti-CEACAM1 mAb (CCM5.01) and characterized its binding to the CEACAM1 receptor. Using this mAb, we assessed the expression of CEACAM1 on four different human melanoma cell lines by western blot and flow cytometry and determined its effect on cell viability in vitro by MTT assay. Furthermore, we evaluated the mAb mechanism of action and found that binding of CEACAM1 with CCM5.01 induced SHP1 phosphorylation and p53 activation resulting in melanoma cell apoptosis. For in vivo studies, a xenograft model of melanoma was performed by injection of Mel-14 cells subcutaneously (s.c.) in SCID/Beige mice followed by intraperitoneal (i.p.) injection of CCM5.01 or of IgG1 isotype control every other day. CCM5.01 treated mice showed a slight but not significant decrease in tumor weight in comparison to the control group. Based on the obtained data, we suggest that activating CEACAM1 on melanoma cells might be a promising novel approach to fight cancers expressing this IR.

Variable Expression of Opa Proteins by Neisseria gonorrhoeae Influences Bacterial Association and Phagocytic Killing by Human Neutrophils

Neisseria gonorrhoeae infection is characterized by local and abundant recruitment of neutrophils. Despite neutrophils' antimicrobial activities, viable N. gonorrhoeae is recovered from infected individuals, leading to the question of how N. gonorrhoeae survives neutrophil attack. One feature impacting N. gonorrhoeae-neutrophil interactions is the phase-variable opacity-associated (Opa) proteins. Most Opa proteins engage human carcinoembryonic antigen-related cell adhesion molecules (CEACAMs) to facilitate bacterial binding and invasion. Neutrophils express two transmembrane CEACAMs, CEACAM1 and the granulocyte-specific CEACAM3. While N. gonorrhoeae isolated from infected individuals is frequently Opa⁺, expression of OpaD from strain FA1090, which interacts with CEACAMs 1 and 3, is associated with reduced N. gonorrhoeae survival after exposure to human neutrophils. In this study, we hypothesized that the receptor-binding capability of individual Opa proteins impacts bacterial survival in the presence of neutrophils. To test this hypothesis, we introduced opa genes that are constitutively expressed into a derivative of strain FA1090 with all 11 opa genes deleted. The engineered genes encode Opa proteins that bind CEACAM1 and -3, CEACAM1 but not CEACAM3, or neither CEACAM1 nor -3. N. gonorrhoeae expressing CEACAM3-binding Opa proteins survived significantly less well than bacteria expressing other Opa proteins when exposed to primary human neutrophils. The CEACAM3-binding N. gonorrhoeae had significantly greater association with and internalization by neutrophils. However, once internalized, bacteria were similarly killed inside neutrophils, regardless of Opa expression. Furthermore, Opa expression did not significantly impact neutrophil granule mobilization. Our findings indicate that the extent to which Opa proteins mediate nonopsonic binding is the predominant determinant of bacterial survival from neutrophils. IMPORTANCE Neisseria gonorrhoeae, the cause of gonorrhea, is an urgent-threat pathogen due to increasing numbers of infections and increased antibiotic resistance. Many surface components of N. gonorrhoeae are phase variable, including the Opa protein family of adhesins and invasins. While Opa protein expression is selected for in vivo, bacteria expressing some Opa proteins are readily killed by neutrophils, which are recruited to sites of infection. The reason for this discrepancy has remained unresolved. Our work shows that Opa-dependent differences in bacterial survival after exposure to primary human neutrophils correlates with Opa-dependent bacterial binding and phagocytosis. These findings underscore how the ability of N. gonorrhoeae to change Opa expression through phase variation contributes to bacterial resistance to neutrophil clearance.

T cell-mediated elimination of cancer cells by blocking CEACAM6–CEACAM1 interaction

Carcinoembryonic antigen-related cell adhesion molecule 6 (CEACAM6), a cell surface receptor, is expressed on normal epithelial tissue and highly expressed in cancers of high unmet medical need, such as non-small cell lung, pancreatic, and colorectal cancer. CEACAM receptors undergo homo- and heterophilic interactions thereby regulating normal tissue homeostasis and angiogenesis, and in cancer, tumor invasion and metastasis. CEACAM6 expression on malignant plasma cells inhibits antitumor activity of T cells, and we hypothesize a similar function on epithelial cancer cells.

The interactions between CEACAM6 and its suggested partner CEACAM1 on T cells were studied. A humanized CEACAM6-blocking antibody, BAY 1834942, was developed and characterized for its immunomodulating effects in co-culture experiments with T cells and solid cancer cells and in comparison to antibodies targeting the immune checkpoints programmed cell death protein 1 (PD-1), programmed death-ligand 1 (PD-L1), and T cell immunoglobulin mucin-3 (TIM-3).

The immunosuppressive activity of CEACAM6 was mediated by binding to CEACAM1 expressed by activated tumor-specific T cells. BAY 1834942 increased cytokine secretion by T cells and T cell-mediated killing of cancer cells. The in vitro efficacy of BAY 1834942 correlated with the degree of CEACAM6 expression on cancer cells, suggesting potential in guiding patient selection. BAY 1834942 was equally or more efficacious compared to blockade of PD-L1, and at least an additive efficacy was observed in combination with anti-PD-1 or anti-TIM-3 antibodies, suggesting an efficacy independent of the PD-1/PD-L1 axis.

In summary, CEACAM6 blockade by BAY 1834942 reactivates the antitumor response of T cells. This warrants clinical evaluation.

The TGF-β/miR-31/CEACAM1-S axis inhibits CD4+ CD25+ Treg differentiation in systemic lupus erythematosus

Defects causing concomitant loss of CD25 expression in regulatory T cells (Tregs) have been identified in systemic lupus erythematosus (SLE). However, the cause of this deficiency is not fully understood. Carcinoembryonic antigen related cell adhesion molecule 1 (CEACAM1), an immune co-receptor, contributes to general T-cell function and activation. Our previous study revealed that CEACAM1 expression was upregulated in peripheral blood mononuclear cells (PBMCs) from patients with SLE. However, its role remains unclear. Herein, we confirmed CEACAM1, especially CEACAM1-S, was upregulated in PBMCs from patients with SLE. CEACAM1-S over-expression inhibits CD4⁺ CD25⁺ Treg differentiation, whereas knockdown of CEACAM1 had the opposite effect in vitro. CEACAM1-S is the target of miR-31. MiR-31 mimic inhibits CEACAM1 expression and enhances CD4⁺ CD25⁺ Treg differentiation, which was reversed by CEACAM1-S over-expression. Moreover, the circulating TGF-β level was upregulated in SLE patients and TGF-β reduced miR-31 expression via enhancing NF-κB activity. Importantly, CEACAM1 and TGF-β mRNA levels were downregulated, while the miR-31 level and the abundance of CD4⁺ CD25⁺ Tregs were increased in inactive patients compared with that in patients with active SLE. In addition, CEACAM1-S expression was positively correlated with the Systemic Lupus Erythematosus Disease Activity Index (SLEDAI) score, while CD4⁺ CD25⁺ Treg abundance and miR-31 level were negatively correlated with the SLEDAI score. In conclusion, reduced activity of miR-31 by TGF-β, via the inhibition of NF-ᴋB, acted to inhibit the differentiation of CD4⁺ CD25⁺ Tregs by directly targeting CEACAM1-S and to promote autoimmunity.

TIM-3 drives temporal differences in restimulation-induced cell death sensitivity in effector CD8+ T cells in conjunction with CEACAM1

Immune homeostasis depends upon effective clearance of pathogens while simultaneously preventing autoimmunity and immunopathology in the host. Restimulation-induced cell death (RICD) is one such mechanism where by activated T cells receive subsequent antigenic stimulation, reach a critical signal threshold through the T cell receptor (TCR), and commit to apoptosis. Many details of this process remain unclear, including the role of co-stimulatory and co-inhibitory proteins that influence the TCR signaling cascade. Here we characterize the role of T cell immunoglobulin and mucin domain containing 3 (TIM-3) in RICD regulation. TIM-3 protected newly activated CD8+ effector T cells from premature RICD during clonal expansion. Surprisingly, however, we found that TIM-3 potentiated RICD in late-stage effector T cells. The presence of TIM-3 increased proximal TCR signaling and proapoptotic protein expression in late-stage effector T cells, with no consistent signaling effects noted in newly activated cells with or without TIM-3. To better explain these differences in TIM-3 function as T cells aged, we characterized the temporal pattern of TIM-3 expression in effector T cells. We found that TIM-3 was expressed on the surface of newly activated effector T cells, but remained largely intracellular in late-stage effector cells. Consistent with this, TIM-3 required a ligand to prevent early RICD, whereas ligand manipulation had no effects at later stages. Of the known TIM-3 ligands, carcinoembryonic antigen-related cell adhesion molecule (CEACAM1) showed the greatest difference in surface expression over time and also protected newly activated cells from premature RICD, with no measurable effects in late-stage effectors. Indeed, CEACAM1 enabled TIM-3 surface expression on T cells, implying a co-dependency for these proteins in protecting expanding T cells from premature RICD. Our findings suggest that co-signaling proteins like TIM-3 and CEACAM1 can alter RICD sensitivity at different stages of the effector T cell response, with important implications for checkpoint blockade therapy.

Modulation of TCR Signaling by Tyrosine Phosphatases: From Autoimmunity to Immunotherapy

Early TCR signaling is dependent on rapid phosphorylation and dephosphorylation of multiple signaling and adaptor proteins, leading to T cell activation. This process is tightly regulated by an intricate web of interactions between kinases and phosphatases. A number of tyrosine phosphatases have been shown to modulate T cell responses and thus alter T cell fate by negatively regulating early TCR signaling. Mutations in some of these enzymes are associated with enhanced predisposition to autoimmunity in humans, and mouse models deficient in orthologous genes often show T cell hyper-activation. Therefore, phosphatases are emerging as potential targets in situations where it is desirable to enhance T cell responses, such as immune responses to tumors. In this review, we summarize the current knowledge about tyrosine phosphatases that regulate early TCR signaling and discuss their involvement in autoimmunity and their potential as targets for tumor immunotherapy.

CEACAM1 regulates CD8+ T cell immunity and protects from severe pathology during Citrobacter rodentium induced colitis

The incidence of gastrointestinal infections continues to increase, and infectious colitis contributes significantly to morbidity and mortality worldwide. Carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1) has been discovered to be strongly involved in the intestinal homeostasis. However, whether intestinal CEACAM1 expression has an impact on the control of infectious colitis remains elusive. Citrobacter rodentium (C. rodentium) is a gram-negative enteric pathogen that induces colonic inflammation in mice, with a critical role for CD4+ T cell but not CD8+ T cell immunity to primary infection. Here, we show that Ceacam1-/- mice are much more susceptible to C. rodentium infection than wildtype mice, which is mediated by a defect in the intestinal barrier and, surprisingly, by a dysregulated CD8+ T cell but not CD4+ T cell response in the colon. CEACAM1 expression is essential for the control of CD8+ T cell immunity, as CEACAM1 deficiency during C. rodentium infection inhibits CD8+ T cell exhaustion. We conclude that CEACAM1 is an important regulator of CD8+ T cell function in the colon, and blocking CEACAM1 signaling to activate CD8+ T cells may have unforeseen side effects.

ERK Activation in CAR T Cells Is Amplified by CD28-Mediated Increase in CD3ζ Phosphorylation

Chimeric antigen receptors (CARs) are engineered receptors that mediate T cell activation. CARs are comprised of activating and co-stimulatory intracellular signaling domains derived from endogenous T cells that initiate signaling required for T cell activation, including ERK activation through the MAPK pathway. Understanding the mechanisms by which co-stimulatory domains influence signaling can help guide the design of next-generation CARs. Therefore, we constructed an experimentally validated computational model of anti-CD19 CARs in T cells bearing the CD3ζ domain alone or in combination with CD28. We performed a systematic analysis to explore the different mechanisms of CD28 co-stimulation on the ERK response time. Comparing these model simulations with experimental data indicates that CD28 primarily influences ERK activation by enhancing the phosphorylation kinetics of CD3ζ. Overall, we present a mechanistic mathematical modeling framework that can be used to gain insights into the mechanism of CAR T cell activation and produce new testable hypotheses.

Unaltered Fungal Burden and Lethality in Human CEACAM1-Transgenic Mice During Candida albicans Dissemination and Systemic Infection

Carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1, CD66a) is a receptor for Candida albicans. It is crucial for the immune response of intestinal epithelial cells to this opportunistic pathogen. Moreover, CEACAM1 is of importance for the mucosal colonization by different bacterial pathogens. We therefore studied the influence of the human CEACAM1 receptor in human CEACAM1-transgenic mice on the C. albicans colonization and infection utilizing a colonization/dissemination and a systemic infection mouse model. Our results showed no alterations in the host response between the transgenic mice and the wild-type littermates to the C. albicans infections. Both mouse strains showed comparable C. albicans colonization and mycobiota, similar fungal burdens in various organs, and a similar survival in the systemic infection model. Interestingly, some of the mice treated with anti-bacterial antibiotics (to prepare them for C. albicans colonization via oral infection) also showed a strong reduction in endogenous fungi instead of the normally observed increase in fungal numbers. This was independent of the expression of human CEACAM1. In the systemic infection model, the human CEACAM1 expression was differentially regulated in the kidneys and livers of Candida-infected transgenic mice. Notably, in the kidneys, a total loss of the largest human CEACAM1 isoform was observed. However, the overwhelming immune response induced in the systemic infection model likely covered any CEACAM1-specific effects in the transgenic animals. In vitro studies using bone marrow-derived neutrophils from both mouse strains also revealed no differences in their reaction to C. albicans. In conclusion, in contrast to bacterial pathogens interacting with CEACAM1 on different mucosal surfaces, the human CEACAM1-transgenic mice did not reveal a role of human CEACAM1 in the in vivo candidiasis models used here. Further studies and different approaches will be needed to reveal a putative role of CEACAM1 in the host response to C. albicans.

CEACAM1 structure and function in immunity and its therapeutic implications

The type I membrane protein receptor carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1) distinctively exhibits significant alternative splicing that allows for tunable functions upon homophilic binding. CEACAM1 is highly expressed in the tumor environment and is strictly regulated on lymphocytes such that its expression is restricted to activated cells where it is now recognized to function in tolerance pathways. CEACAM1 is also an important target for microbes which have co-opted these attributes of CEACAM1 for the purposes of invading the host and evading the immune system. These properties, among others, have focused attention on CEACAM1 as a unique target for immunotherapy in autoimmunity and cancer. This review examines recent structural information derived from the characterization of CEACAM1:CEACAM1 interactions and heterophilic modes of binding especially to microbes and how this relates to CEACAM1 function. Through this, we aim to provide insights into targeting CEACAM1 for therapeutic intervention.

Protein Tyrosine Phosphatases: Regulators of CD4 T Cells in Inflammatory Bowel Disease

Protein tyrosine phosphatases (PTPs) play a critical role in co-ordinating the signaling networks that maintain lymphocyte homeostasis and direct lymphocyte activation. By dephosphorylating tyrosine residues, PTPs have been shown to modulate enzyme activity and both mediate and disrupt protein-protein interactions. Through these molecular mechanisms, PTPs ultimately impact lymphocyte responses to environmental cues such as inflammatory cytokines and chemokines, as well as antigenic stimulation. Mouse models of acute and chronic intestinal inflammation have been shown to be exacerbated in the absence of PTPs such as PTPN2 and PTPN22. This increase in disease severity is due in part to hyper-activation of lymphocytes in the absence of PTP activity. In accordance, human PTPs have been linked to intestinal inflammation. Genome wide association studies (GWAS) identified several PTPs within risk loci for inflammatory bowel disease (IBD). Therapeutically targeting PTP substrates and their associated signaling pathways, such as those implicated in CD4⁺ T cell responses, has demonstrated clinical efficacy. The current review focuses on the role of PTPs in controlling CD4⁺ T cell activity in the intestinal mucosa and how disruption of PTP activity in CD4⁺ T cells can contribute to intestinal inflammation.

CEACAM1 in Liver Injury, Metabolic and Immune Regulation

Carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1) is a transmembrane glycoprotein that is expressed on epithelial, endothelial and immune cells. CEACAM1 is a differentiation antigen involved in the maintenance of epithelial polarity that is induced during hepatocyte differentiation and liver regeneration. CEACAM1 regulates insulin sensitivity by promoting hepatic insulin clearance, and controls liver tolerance and mucosal immunity. Obese insulin-resistant humans with non-alcoholic fatty liver disease manifest loss of hepatic CEACAM1. In mice, deletion or functional inactivation of CEACAM1 impairs insulin clearance and compromises metabolic homeostasis which initiates the development of obesity and hepatic steatosis and fibrosis with other features of non-alcoholic steatohepatitis, and adipogenesis in white adipose depot. This is followed by inflammation and endothelial and cardiovascular dysfunctions. In obstructive and inflammatory liver diseases, soluble CEACAM1 is shed into human bile where it can serve as an indicator of liver disease. On immune cells, CEACAM1 acts as an immune checkpoint regulator, and deletion of Ceacam1 gene in mice causes exacerbation of inflammation and hyperactivation of myeloid cells and lymphocytes. Hence, hepatic CEACAM1 resides at the central hub of immune and metabolic homeostasis in both humans and mice. This review focuses on the regulatory role of CEACAM1 in liver and biliary tract architecture in health and disease, and on its metabolic role and function as an immune checkpoint regulator of hepatic inflammation.

Characterization of murine CEACAM1 in vivo reveals low expression on CD8+ T cells and no tumor growth modulating activity by anti-CEACAM1 mAb CC1

Carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1) has been reported to mediate both tumorigenic and anti-tumor effects in vivo. Blockade of the CEACAM1 signaling pathway has recently been implicated as a novel mechanism for cancer immunotherapy. CC1, a mouse anti-CEACAM1 monoclonal antibody (mAb), has been widely used as a pharmacological tool in preclinical studies to inform on CEACAM1 pathway biology although limited data are available on its CEACAM1 blocking characteristics or pharmacodynamic-pharmacokinetic profiles. We sought to investigate CEACAM1 expression on mouse tumor and immune cells, characterize CC1 mAb binding, and evaluate CC1 in syngeneic mouse oncology models as a monotherapy and in combination with an anti-PD-1 mAb. CEACAM1 expression was observed at high levels on neutrophils, NK cells and myeloid-derived suppressor cells (MDSCs), while the expression on tumor-infiltrating CD8+ T cells was low. Unexpectedly, rather than blocking, CC1 facilitated binding of soluble CEACAM1 to CEACAM1 expressing cells. No anti-tumor effects were observed in CT26, MBT2 or A20 models when tested up to 30 mg/kg dose, a dose that was estimated to achieve >90% target engagement in vivo. Taken together, tumor infiltrating CD8+ T cells express low levels of CEACAM1 and CC1 Ab mediates no or minimal anti-tumor effects in vivo, as a monotherapy or in combination with anti-PD-1 treatment.

CEACAM1 promotes CD8+ T cell responses and improves control of a chronic viral infection

Dysfunction of CD8⁺ T cells can lead to the development of chronic viral infection. Identifying mechanisms responsible for such T cell dysfunction is therefore of great importance to understand how to prevent persistent viral infection. Here we show using lymphocytic choriomeningitis virus (LCMV) infection that carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1) is fundamental for recruiting lymphocyte-specific protein kinase (Lck) into the T cell receptor complex to form an efficient immunological synapse. CEACAM1 is essential for activation of CD8⁺ T cells, and the absence of CEACAM1 on virus-specific CD8⁺ T cells limits the antiviral CD8⁺ T cell response. Treatment with anti-CEACAM1 antibody stabilizes Lck in the immunological synapse, prevents CD8⁺ T cell exhaustion, and improves control of virus infection in vivo. Treatment of human virus-specific CD8⁺ T cells with anti-CEACAM1 antibody similarly enhances their proliferation. We conclude that CEACAM1 is an important regulator of virus-specific CD8⁺ T cell functions in mice and humans and represents a promising therapeutic target for modulating CD8⁺ T cells.

Chronic viral infections are frequently associated with the dysfunction of CD8⁺ T cells which includes loss of function and results in CD8⁺ T cell exhaustion. Here the authors show a role of CEACAM1 in promoting responsive CD8⁺ T cells in the context of a chronic lymphocytic choriomeningitis virus (LCMV) infection model.

CEACAM1 as a multi-purpose target for cancer immunotherapy

CEACAM1 is an extensively studied cell surface molecule with established functions in multiple cancer types, as well as in various compartments of the immune system. Due to its multi-faceted role as a recently appreciated immune checkpoint inhibitor and tumor marker, CEACAM1 is an attractive target for cancer immunotherapy. Herein, we highlight CEACAM1's function in various immune compartments and cancer types, including in the context of metastatic disease. This review outlines CEACAM1's role as a therapeutic target for cancer treatment in light of these properties.

CEACAM1 long isoform has opposite effects on the growth of human mastocytosis and medullary thyroid carcinoma cells

Carcinoembryonic antigen‐related cell adhesion molecule 1 (CEACAM1) is expressed in a number of tumor cell types. The immunoreceptor tyrosine‐based inhibitory motif (ITIM)‐containing isoforms of this molecule which possess a long cytoplasmic tail (CEACAM1‐L) generally play inhibitory roles in cell function by interacting with Src homology 2 domain‐containing tyrosine phosphatase (SHP)‐1 and/or SHP‐2. Src family kinases (SFKs) are also known to bind to and phosphorylate CEACAM1‐L isoforms. Here, we report that CEACAM1 was uniquely expressed at high levels in both human neoplastic mast cells (mastocytosis) and medullary thyroid carcinoma cell (MTC) lines, when compared with their expression in nonneoplastic mast cells or nonneoplastic C cells. This expression was mainly derived from CEACAM1‐L isoforms based upon assessment of CEACAM1 mRNA expression. CEACAM1 knockdown upregulated cell growth of HMC1.2 cells harboring KIT mutations detected in clinical mastocytosis, whereas downregulated the growth of TT cells harboring RET mutations detected in clinical MTCs. Immunoblotting, ELISA and immunoprecipitaion analysis showed that activated SHP‐1 is preferentially associated with CEACAM1 in HMC1.2 cells harboring KIT mutations, whereas Src family kinases (SFKs) are preferentially associated with CEACAM1 in TT cells harboring RET mutations. These studies suggest that the dominantly interacting proteins SHP1 or SFK determine whether CEACAM1‐L displays a positive or negative role in tumor cells.

CEACAM1 controls the EMT switch in murine mammary carcinoma in vitro and in vivo

We analyzed the molecular basis for carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1)-controlled inhibition of epithelial-mesenchymal transition (EMT) in a mouse model for mammary adenocarcinoma (WAP-T mice). We demonstrate that silencing of CEACAM1 in WAP-T tumor-derived G-2 cells induces epithelial-mesenchymal plasticity (EMP), as evidenced by typical changes of gene expression, morphology and increased invasion. In contrast, reintroduction of CEACAM1 into G-2 cells reversed up-regulation of genes imposing mesenchymal transition, as well as cellular invasion. We identified the Wnt-pathway as target for CEACAM1-mediated repression of EMT. Importantly, β-catenin phosphorylation status and transcriptional activity strongly depend on CEACAM1 expression: CEACAM1high G-2 cells displayed enhanced phosphorylation of β-catenin at S33/S37/T41 and decreased phosphorylation at Y86, thereby inhibiting canonical Wnt/β-catenin signaling. We identified Src-homology 2 domain-containing phosphatase 2 (SHP-2) as a critical binding partner of CEACAM1 that could modulate β-catenin Y86 phosphorylation. Hence, CEACAM1 serves as a scaffold that controls membrane proximal β-catenin signaling. In vivo, mammary tumors of WAP-T/CEACAM1null mice displayed increased nuclear translocation of β-catenin and a dramatically enhanced metastasis rate compared to WAP-T mice. Hence, CEACAM1 controls EMT in vitro and in vivo by site-specific regulation of β-catenin phosphorylation. Survival analyses of human mammary carcinoma patients corroborated these data, indicating that CEACAM1 is a prognostic marker for breast cancer survival.

Neisserial Opa Protein-CEACAM Interactions: Competition for Receptors as a Means of Bacterial Invasion and Pathogenesis

Carcino-embryonic antigen-like cellular adhesion molecules (CEACAMs), members of the immunoglobulin superfamily, are responsible for cell-cell interactions and cellular signaling events. Extracellular interactions with CEACAMs have the potential to induce phagocytosis, as is the case with pathogenic Neisseria bacteria. Pathogenic Neisseria species express opacity-associated (Opa) proteins, which interact with a subset of CEACAMs on human cells, and initiate the engulfment of the bacterium. We demonstrate that recombinant Opa proteins reconstituted into liposomes retain the ability to recognize and interact with CEACAMs in vitro but do not maintain receptor specificity compared to that of Opa proteins natively expressed by Neisseria gonorrhoeae. We report that two Opa proteins interact with CEACAMs with nanomolar affinity, and we hypothesize that this high affinity is necessary to compete with the native CEACAM homo- and heterotypic interactions in the host. Understanding the mechanisms of Opa protein-receptor recognition and engulfment enhances our understanding of Neisserial pathogenesis. Additionally, these mechanisms provide insight into how human cells that are typically nonphagocytic can utilize CEACAM receptors to internalize exogenous matter, with implications for the targeted delivery of therapeutics and development of imaging agents.

Negative immune checkpoints on T lymphocytes and their relevance to cancer immunotherapy

The term 'inhibitory checkpoint' refers to the broad spectrum of co-receptors expressed by T cells that negatively regulate T cell activation thus playing a crucial role in maintaining peripheral self-tolerance. Co-inhibitory receptor ligands are highly expressed by a variety of malignancies allowing evasion of anti-tumour immunity. Recent studies demonstrate that manipulation of these co-inhibitory pathways can remove the immunological brakes that impede endogenous immune responses against tumours. Antibodies that block the interactions between co-inhibitory receptors and their ligands have delivered very promising clinical responses, as has been shown by recent successful trials targeting the CTLA-4 and PD-1 pathways. In this review, we discuss the mechanisms of action and expression pattern of co-inhibitory receptors on different T cells subsets, emphasising differences between CD4(+) and CD8(+) T cells. We also summarise recent clinical findings utilising immune checkpoint blockade.

NKp46 regulates the production of serine proteases and IL-22 in human mast cells in urticaria pigmentosa

NKp46 (natural cytotoxic receptor 1/CD335) is expressed on natural killer cells and Th2-type innate lymphocytes. However, NKp46 expression in human mast cells has not yet been reported. Here, we explored the expression of, and possible role played by, NKp46 in such cells. NKp46 protein was expressed in human mast cells in urticaria pigmentosa principally of the tryptase-positive/chymase-negative type (MCT), but not in human non-neoplastic skin mast cells of the tryptase-positive/chymase-positive (MCTC) type. NKp46 expression was also evident in the human neoplastic mast cell line HMC1.2. NKp46 knockdown changed the phenotype of this cell line from MCT to MCTC and downregulated GrB production, but did not influence IL-22 production. An agonistic anti-NKp46 antibody upregulated production of GrB and IL-22, but did not change the MCT-like phenotype of HMC1.2 cells. NKp46 was thus involved in the production of serine proteases and IL-22 in human mast cells.

Expression of Opacity Proteins Interferes with the Transmigration of Neisseria gonorrhoeae across Polarized Epithelial Cells

Neisseria gonorrhoeae (GC) establishes infection at the mucosal surface of the human genital tract, most of which is lined with polarized epithelial cells. GC can cause localized as well as disseminated infections, leading to various complications. GC constantly change their surface structures via phase and antigenic variation, which has been implicated as a means for GC to establish infection at various anatomic locations of male and female genital tracks. However, the exact contribution of each surface molecule to bacterial infectivity remains elusive due to their phase variation. Using a GC derivative that is genetically devoid of all opa genes (MS11∆Opa), this study shows that Opa expression interferes with GC transmigration across polarized human epithelial cells. MS11∆Opa transmigrates across polarized epithelial cells much faster and to a greater extent than MS11Opa+, while adhering at a similar level as MS11Opa+. When MS11Opa+, able to phase vary Opa expression, was inoculated, only those bacteria that turn off Opa expression transmigrate across the polarized epithelial monolayer. Similar to bacteria alone or co-cultured with non-polarized epithelial cells, MS11∆Opa fails to form large microcolonies at the apical surface of polarized epithelial cells. Apical inoculation of MS11Opa+, but not MS11∆Opa, induces the recruitment of the Opa host-cell receptor carcinoembryonic antigen–related cell adhesion molecules (CEACAMs) to the apical junction and the vicinity of bacterial adherent sites. Our results suggest that Opa expression limits gonococcal ability to invade into subepithelial tissues by forming tight interactions with neighboring bacteria and by inducing CEACAM redistribution to cell junctions.

A multimeric carcinoembryonic antigen signal inhibits the activation of human T cells by a SHP-independent mechanism: a potential mechanism for tumor-mediated suppression of T-cell immunity

Carcinoembryonic antigen (CEA) is a well-known tumor antigen that is found in the serum of patients with various cancers and is correlated with an increased risk of cancer recurrence and metastasis. To understand the tumor environment and to develop antitumor therapies, CEA has been studied as an antigen to activate/tolerate specific T cells. In this study, we show that CEA can function as a coinhibitory molecule and can inhibit the activation of human peripheral blood mononucleated cell-derived T cells. The addition of CEA-overexpressing tumor cells or immobilized CEA dampened both cell proliferation and the expression of IL-2 and CD69 expression in T cells after TCR stimulation. The phosphorylation of ERK and translocation of NFAT were hampered in these cells, whereas the phosphorylation of proximal TCR signaling molecules such as ZAP70 and phospholipase Cγ was not affected by immobilized CEA. To determine the relevance of carcinoembryonic antigen-related cell adhesion molecule-1 and Src homology region 2 domain-containing phosphatase (SHP) molecules to CEA-mediated suppression, we tested the effect of the SHP inhibitor, NSC-87877, on CEA-mediated suppression of T cells; however, it did not reverse the effect of CEA. Collectively, these results indicate that CEA can function as a modulator of T-cell responses suggesting a novel mechanism of tumor evasion.

CEACAM1 induces B-cell survival and is essential for protective antiviral antibody production

B cells are essential for antiviral immune defence because they produce neutralizing antibodies, present antigen and maintain the lymphoid architecture. Here we show that intrinsic signalling of CEACAM1 is essential for generating efficient B-cell responses. Although CEACAM1 exerts limited influence on the proliferation of B cells, expression of CEACAM1 induces survival of proliferating B cells via the BTK/Syk/NF-κB-axis. The absence of this signalling cascade in naive Ceacam1^−/− mice limits the survival of B cells. During systemic infection with cytopathic vesicular stomatitis virus, Ceacam1^−/− mice can barely induce neutralizing antibody responses and die early after infection. We find, therefore, that CEACAM1 is a crucial regulator of B-cell survival, influencing B-cell numbers and protective antiviral antibody responses.

Antibody responses are regulated by selective survival of B cells with proper antigen specificity. Here the authors show that CEACAM1 is critical for B-cell survival during homeostasis and antiviral responses.

Protective mucosal immunity mediated by epithelial CD1d and IL-10

The mechanisms by which mucosal homeostasis is maintained are of central importance to inflammatory bowel disease. Critical to these processes is the intestinal epithelial cell (IEC), which regulates immune responses at the interface between the commensal microbiota and the host. CD1d presents self and microbial lipid antigens to natural killer T (NKT) cells, which are involved in the pathogenesis of colitis in animal models and human inflammatory bowel disease. As CD1d crosslinking on model IECs results in the production of the important regulatory cytokine interleukin (IL)-10 (ref. 9), decreased epithelial CD1d expression--as observed in inflammatory bowel disease--may contribute substantially to intestinal inflammation. Here we show in mice that whereas bone-marrow-derived CD1d signals contribute to NKT-cell-mediated intestinal inflammation, engagement of epithelial CD1d elicits protective effects through the activation of STAT3 and STAT3-dependent transcription of IL-10, heat shock protein 110 (HSP110; also known as HSP105), and CD1d itself. All of these epithelial elements are critically involved in controlling CD1d-mediated intestinal inflammation. This is demonstrated by severe NKT-cell-mediated colitis upon IEC-specific deletion of IL-10, CD1d, and its critical regulator microsomal triglyceride transfer protein (MTP), as well as deletion of HSP110 in the radioresistant compartment. Our studies thus uncover a novel pathway of IEC-dependent regulation of mucosal homeostasis and highlight a critical role of IL-10 in the intestinal epithelium, with broad implications for diseases such as inflammatory bowel disease.

Downregulation of inhibitory SRC homology 2 domain-containing phosphatase-1 (SHP-1) leads to recovery of T cell responses in elderly

BACKGROUND

Immune responses are generally impaired in aged mammals. T cells have been extensively studied in this context due to the initial discovery of their reduced proliferative capacity with aging. The decreased responses involve altered signaling events associated with the early steps of T cell activation. The underlying causes of these changes are not fully understood but point to alterations in assembly of the machinery for T cell activation. Here, we have tested the hypothesis that the T cell pool in elderly subjects displayed reduced functional capacities due to altered negative feedback mechanisms that participate in the regulation of the early steps of T cell activation. Such conditions tip the immune balance in favor of altered T cell activation and a related decreased response in aging.

RESULTS

We present evidence that the tyrosine phosphatase SHP-1, a key regulator of T cell signal transduction machinery is, at least in part, responsible for the impaired T cell activation in aging. We used tyrosine-specific mAbs and Western blot analysis to show that a deregulation of the Csk/PAG loop in activated T cells from elderly individuals favored the inactive form of tyrosine-phosphorylated Lck (Y505). Confocal microscopy analysis revealed that the dynamic movements of these regulatory proteins in lipid raft microdomains was altered in T cells of aged individuals. Enzymic assays showed that SHP-1 activity was upregulated in T cells of aged donors, in contrast to young subjects. Pharmacological inhibition of SHP-1 resulted in recovery of TCR/CD28-dependent lymphocyte proliferation and IL-2 production of aged individuals to levels approaching those of young donors. Significant differences in the active (Y394) and inactive (Y505) phosphorylation sites of Lck in response to T cell activation were observed in elderly donors as compared to young subjects, independently of CD45 isoform expression.

CONCLUSIONS

Our data suggest that the role of SHP-1 in T cell activation extends to its increased effect in negative feedback in aging. Modulation of SHP-1 activity could be a target to restore altered T cell functions in aging. These observations could have far reaching consequences for improvement of immunosenescence and its clinical consequences such as infections, altered response to vaccination.

Shp1 regulates T cell homeostasis by limiting IL-4 signals

Absence of the phosphatase Shp1 in T cells does not affect the TCR signaling threshold but results in IL-4 sensitivity and memory phenotype cells.

The protein-tyrosine phosphatase Shp1 is expressed ubiquitously in hematopoietic cells and is generally viewed as a negative regulatory molecule. Mutations in Ptpn6, which encodes Shp1, result in widespread inflammation and premature death, known as the motheaten (me) phenotype. Previous studies identified Shp1 as a negative regulator of TCR signaling, but the severe systemic inflammation in me mice may have confounded our understanding of Shp1 function in T cell biology. To define the T cell–intrinsic role of Shp1, we characterized mice with a T cell–specific Shp1 deletion (Shp1^fl/fl CD4-cre). Surprisingly, thymocyte selection and peripheral TCR sensitivity were unaltered in the absence of Shp1. Instead, Shp1^fl/fl CD4-cre mice had increased frequencies of memory phenotype T cells that expressed elevated levels of CD44. Activation of Shp1-deficient CD4⁺ T cells also resulted in skewing to the Th2 lineage and increased IL-4 production. After IL-4 stimulation of Shp1-deficient T cells, Stat 6 activation was sustained, leading to enhanced Th2 skewing. Accordingly, we observed elevated serum IgE in the steady state. Blocking or genetic deletion of IL-4 in the absence of Shp1 resulted in a marked reduction of the CD44^hi population. Therefore, Shp1 is an essential negative regulator of IL-4 signaling in T lymphocytes.

CEACAM1 on activated NK cells inhibits NKG2D-mediated cytolytic function and signaling

Carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1) is expressed on activated natural killer (NK) cells wherein it inhibits lysis of CEACAM1-bearing tumor cell lines. The mechanism for this is unknown. Here, we show that interleukin-2-induced expression of CEACAM1 on both mouse and primary human NK cells impairs the ability of NK gene complex group 2 member D (NKG2D) to stimulate cytolysis of CEACAM1-bearing cells. This process requires the expression of CEACAM1 on the NK cells and on the tumor cells, which is consistent with the involvement of trans-homophilic interactions between CEACAM1. Mechanistically, co-engagement of NKG2D and CEACAM1 results in a biochemical association between these two surface receptors and the recruitment of Src homology phosphatase 1 by CEACAM1 that leads to dephosphorylation of the guanine nucleotide exchange factor Vav1 and blockade of downstream signaling that is associated with the initiation of cytolysis. Thus, CEACAM1 on activated NK cells functions as an inhibitory receptor for NKG2D-mediated cytolysis, which has important implications for understanding the means by which CEACAM1 expression adversely affects tumor immunity.

CEACAM1 regulates Fas-mediated apoptosis in Jurkat T-cells via its interaction with β-catenin

CEACAM1 (Carcinoembryonic Antigen Cell Adhesion molecule 1), an activation induced cell surface marker of T-cells, modulates the T-cell immune response by inhibition of the T-cell and IL-2 receptors. Since T-cells undergo activation induced cell death via Fas activation, it was of interest to determine if this pathway was also affected by CEACAM1. Previously, we identified a novel biochemical interaction between CEACAM1 and the armadillo repeats of β-catenin in Jurkat cells, in which two critical residues, H469 and K470 of the cytoplasmic domain of CEACAM1-4L played an essential role; while in other studies, β-catenin was shown to regulate Fas-mediated apoptosis in Jurkat cells. CEACAM1 expression in Jurkat cells leads to the re-distribution of β-catenin to the actin cytoskeleton as well as inhibition of β-catenin tyrosine phosphorylation and its degradation after Fas stimulation. As a result, Fas-mediated apoptosis in these cells was inhibited. The K470A mutation of CEACAM1 partially rescued the inhibitory effect, in agreement with the prediction that a CEACAM1-β-catenin interaction pathway is involved. Although CEACAM1 has two ITIMs, they were not tyrosine-phosphorylated upon Fas ligation, indicating an ITIM independent mechanism; however, mutation of the critical residue S508, located between the ITIMs, to aspartic acid and a prerequisite for ITIM activation, abrogates the inhibitory activity of CEACAM1 to Fas-mediated apoptosis. Since Fas-mediated apoptosis is a major form of activation-induced cell death, our finding supports the idea that CEACAM1 is a general inhibitory molecule for T-cell activation utilizing a variety of pathways.

The short isoform of the CEACAM1 receptor in intestinal T cells regulates mucosal immunity and homeostasis via Tfh cell induction

Carcinoembryonic antigen cell adhesion molecule like I (CEACAM1) is expressed on activated T cells and signals through either a long (L) cytoplasmic tail containing immune receptor tyrosine based inhibitory motifs, which provide inhibitory function, or a short (S) cytoplasmic tail with an unknown role. Previous studies on peripheral T cells show that CEACAM1-L isoforms predominate with little to no detectable CEACAM1-S isoforms in mouse and human. We show here that this was not the case in tissue resident T cells of intestines and gut associated lymphoid tissues, which demonstrated predominant expression of CEACAM1-S isoforms relative to CEACAM1-L isoforms in human and mouse. This tissue resident predominance of CEACAM1-S expression was determined by the intestinal environment where it served a stimulatory function leading to the regulation of T cell subsets associated with the generation of secretory IgA immunity, the regulation of mucosal commensalism, and defense of the barrier against enteropathogens.

Regulation of TCR signalling by tyrosine phosphatases: from immune homeostasis to autoimmunity

More than half of the known protein tyrosine phosphatases (PTPs) in the human genome are expressed in T cells, and significant progress has been made in elucidating the biology of these enzymes in T-cell development and function. Here we provide a systematic review of the current understanding of the roles of PTPs in T-cell activation, providing insight into their mechanisms of action and regulation in T-cell receptor signalling, the phenotypes of their genetically modified mice, and their possible involvement in T-cell-mediated autoimmune disease. Our projection is that the interest in PTPs as mediators of T-cell homeostasis will continue to rise with further functional analysis of these proteins, and PTPs will be increasingly considered as targets of immunomodulatory therapies.

Abrogation of SRC homology region 2 domain-containing phosphatase 1 in tumor-specific T cells improves efficacy of adoptive immunotherapy by enhancing the effector function and accumulation of short-lived effector T cells in vivo

T cell expression of inhibitory proteins can be a critical component for the regulation of immunopathology owing to self-reactivity or potentially exuberant responses to pathogens, but it may also limit T cell responses to some malignancies, particularly if the tumor Ag being targeted is a self-protein. We found that the abrogation of Src homology region 2 domain-containing phosphatase-1 (SHP-1) in tumor-reactive CD8(+) T cells improves the therapeutic outcome of adoptive immunotherapy in a mouse model of disseminated leukemia, with benefit observed in therapy employing transfer of CD8(+) T cells alone or in the context of also providing supplemental IL-2. SHP-1(-/-) and SHP-1(+/+) effector T cells were expanded in vitro for immunotherapy. Following transfer in vivo, the SHP-1(-/-) effector T cells exhibited enhanced short-term accumulation, followed by greater contraction, and they ultimately formed similar numbers of long-lived, functional memory cells. The increased therapeutic effectiveness of SHP-1(-/-) effector cells was also observed in recipients that expressed the tumor Ag as a self-antigen in the liver, without evidence of inducing autoimmune toxicity. SHP-1(-/-) effector CD8(+) T cells expressed higher levels of eomesodermin, which correlated with enhanced lysis of tumor cells. Furthermore, reduction of SHP-1 expression in tumor-reactive effector T cells by retroviral transduction with vectors that express SHP-1-specific small interfering RNA, a translatable strategy, also exhibited enhanced antitumor activity in vivo. These studies suggest that abrogating SHP-1 in effector T cells may improve the efficacy of tumor elimination by T cell therapy without affecting the ability of the effector cells to persist and provide a long-term response.

Novel anti-melanoma immunotherapies: disarming tumor escape mechanisms

The immune system fights cancer and sometimes temporarily eliminates it or reaches an equilibrium stage of tumor growth. However, continuous immunological pressure also selects poorly immunogenic tumor variants that eventually escape the immune control system. Here, we focus on metastatic melanoma, a highly immunogenic tumor, and on anti-melanoma immunotherapies, which recently, especially following the FDA approval of Ipilimumab, gained interest from drug development companies. We describe new immunomodulatory approaches currently in the development pipeline, focus on the novel CEACAM1 immune checkpoint, and compare its potential to the extensively described targets, CTLA4 and PD1. This paper combines multi-disciplinary approaches and describes anti-melanoma immunotherapies from molecular, medical, and business angles.

CEACAM1 negatively regulates IL-1β production in LPS activated neutrophils by recruiting SHP-1 to a SYK-TLR4-CEACAM1 complex

LPS-activated neutrophils secrete IL-1β by activation of TLR-4. Based on studies in macrophages, it is likely that ROS and lysosomal destabilization regulated by Syk activation may also be involved. Since neutrophils have abundant expression of the ITIM-containing co-receptor CEACAM1 and Gram-negative bacteria such as Neisseria utilize CEACAM1 as a receptor that inhibits inflammation, we hypothesized that the overall production of IL-1β in LPS treated neutrophils may be negatively regulated by CEACAM1. We found that LPS treated neutrophils induced phosphorylation of Syk resulting in the formation of a complex including TLR4, p-Syk, and p-CEACAM1, which in turn, recruited the inhibitory phosphatase SHP-1. LPS treatment leads to ROS production, lysosomal damage, caspase-1 activation and IL-1β secretion in neutrophils. The absence of this regulation in Ceacam1^−/− neutrophils led to hyper production of IL-1β in response to LPS. The hyper production of IL-1β was abrogated by in vivo reconstitution of wild type but not ITIM-mutated CEACAM1 bone marrow stem cells. Blocking Syk activation by kinase inhibitors or RNAi reduced Syk phosphorylation, lysosomal destabilization, ROS production, and caspase-1 activation in Ceacam1^−/− neutrophils. We conclude that LPS treatment of neutrophils triggers formation of a complex of TLR4 with pSyk and pCEACAM1, which upon recruitment of SHP-1 to the ITIMs of pCEACAM1, inhibits IL-1β production by the inflammasome. Thus, CEACAM1 fine-tunes IL-1β production in LPS treated neutrophils, explaining why the additional utilization of CEACAM1 as a pathogen receptor would further inhibit inflammation.

Pathogens often evade the immune system by directly binding to and inhibiting neutrophils, abundant white cells that accumulate at the site of infection. For example Gram-negative Neisseria pathogens, such as those that cause gonorrhea or meningitis, bind the neutrophil receptor CEACAM1. Gram-negative bacteria express lipopolysaccharide (LPS) that interacts with toll-like receptor-4 (TLR4) on neutrophils. Since CEACAM1 is an inhibitory receptor, we hypothesized that LPS activation of TLR4 would be inhibited. In this paper we show that this is the case and that the mechanism of LPS inhibition involves induction of a complex between the LPS receptor TLR4, CEACAM1 and an activating kinase called Syk. In the presence of CEACAM1, an inhibitory phosphatase (opposes the kinase) is recruited to the complex that prevents the activation of Syk. The net effect is the inhibition of the pathway that normally leads to the production of the pro-inflammatory cytokine IL-1β. We show that this inhibition is lost in CEACAM1 deficient neutrophils leading to hyper production of IL-1β. We think that CEACAM1 fine-tunes the normal inflammatory response at the site of infection preventing hyper-inflammation, but in the case of Gram-negative pathogens that actually bind to neutrophils, inflammation is further blunted, favoring the infectious process.

CEACAM1 dampens antitumor immunity by down-regulating NKG2D ligand expression on tumor cells

By retaining NKG2D ligands within tumor cells, carcinoembryonic antigen–related cell adhesion molecule 1 (CEACAM1) facilitates tumor cell escape from NK cell–mediated cytolysis in vitro and in vivo.

Although carcinoembryonic antigen (CEA)–related cell adhesion molecule 1 (CEACAM1) has been viewed as a tumor suppressor, increasing clinical evidence shows that high levels of CEACAM1 expression on tumors correlates with poor prognosis and high risk of metastasis. Here, we examined the consequences of CEACAM1 expression on tumor cells. We show that tumor cell–associated CEACAM1 causes intracellular retention of various NKG2D ligands in mouse and human tumor cells. CEACAM1-silenced tumor cells expressed more cell surface NKG2D ligands and exhibited greater sensitivity to natural killer cell–mediated cytolysis in vitro and rejection in vivo. Our studies reveal a novel mechanism through which CEACAM1-bearing tumor cells may escape immune-surveillance.

Defining the roles of human carcinoembryonic antigen-related cellular adhesion molecules during neutrophil responses to Neisseria gonorrhoeae

Symptomatic infection of humans with Neisseria gonorrhoeae is characterized by a neutrophil-rich cervical or urethral exudate, suggesting that neutrophils are important both for the clearance of these bacteria and for the pathogenesis of gonorrhea. Neisseria interacts with neutrophils through ligation of human carcinoembryonic antigen related-cellular adhesion molecules (CEACAMs) by their surface-expressed Opa proteins, resulting in bacterial binding, engulfment, and neutrophil activation. Multiple CEACAMs are expressed by human neutrophils, and yet their coexpression has precluded understanding of the relative contribution of each CEACAM to functional responses of neutrophils during neisserial infection. In this work, we directly address the role of each CEACAM during infection by introducing individual human CEACAMs into a differentiated murine MPRO cell line-derived neutrophil model. Murine neutrophils cannot bind the human-restricted Neisseria; however, we show that introducing any of the Opa-binding CEACAMs of human neutrophils (CEACAM1, CEACAM3, and CEACAM6) allows binding and entry of Neisseria into murine neutrophils. While CEACAM1- and CEACAM6-expressing neutrophils bind more bacteria, neisserial uptake via these two receptors unexpectedly proceeds without appreciable neutrophil activation. In stark contrast, neisserial engulfment via CEACAM3 recapitulates the oxidative burst and intracellular granule release seen during human neutrophil infection. Finally, by coexpressing multiple CEACAMs in our model, we show that the expression of CEACAM1 and CEACAM6 potentiate, rather than hinder, CEACAM3-dependent responses of neutrophils, exposing a cooperative role for this family of proteins during neisserial infection of neutrophils. These observations illustrate a divergence in function of CEACAMs in neutrophils and implicate the human-restricted CEACAM3 in the neutrophil innate response to neisserial infection.

Establishment of a human CEACAM1 transgenic mouse model for the study of gonococcal infections

Neisseria gonorrhoeae is the causative microorganism for the sexually transmitted disease (STD) gonorrhea and humans are its only natural host. An animal model would be a useful tool for gonorrhea research, therefore we developed the hCEACAM1 transgenic mice, using an eukaryotic expression vector, pCDPCAM1-GI. This construct was microinjected into the zygotes of C57BL/6 mice and 22 F0 generation transgenic mice were obtained. Four (lines 50, 53, 54, and 59) of the F0 generation were found to carry the transgene by PCR and sequence analysis, respectively. Western blotting and Fluorescence-Activated Cell Sorting Analysis demonstrated that hCEACAM1 was expressed on the cell membrane of various tissues in the line 53 transgenic mouse. To initiate the disease in the animal model, the F2 or F3 transgenic mice were inoculated with N. gonorrhoeae intravaginally. Compared with normal mice, N. gonorrhoeae can successfully infect and cause inflammation in the transgenic mice. These data suggested the feasibility of using hCEACAM1 transgenic mice as an animal model for gonococcal infections.

Tumor-induced disruption of proximal TCR-mediated signal transduction in tumor-infiltrating CD8+ lymphocytes inactivates antitumor effector phase

The presence in cancer tissue of Ag-specific, activated tumor infiltrating CD8(+) T cells proves that tumors express Ags capable of eliciting immune response. Therefore, in general, tumor escape from immune-mediated clearance is not attributable to immunological ignorance. However, tumor-infiltrating lymphocytes are defective in effector phase function, demonstrating tumor-induced immune suppression that likely underlies tumor escape. Since exocytosis of lytic granules is dependent upon TCR-mediated signal transduction, it is a reasonable contention that tumors may induce defective signal transduction in tumor infiltrating T cells. In this review, we consider the biochemical basis for antitumor T cell dysfunction, focusing on the role of inhibitory signaling receptors in restricting TCR-mediated signaling in tumor-infiltrating lymphocytes.

Expression of CD66 in non-Hodgkin lymphomas and multiple myeloma

OBJECTIVES

⁹⁰Y-labeled anti-CD66b monoclonal antibody clone BW 250/183 was developed for treatment of tumors. The aim of the study was the analysis of CD66 expression in lymphoproliferative malignancies to expand the potential of anti-CD66-based therapy.

PATIENTS AND METHODS

Bone marrow samples from 260 patients were examined for the expression of CD66 on tumor cells in 104 B-chronic lymphocytic leukemias (B-CLL), 28 mantle cell lymphomas (MCL), 22 follicular lymphomas (FCL), 15 marginal zone lymphomas (MZL), 12 lymphoplasmacytic lymphomas (LPL), 13 diffuse large B cell lymphomas (DLBCL), 4 T-non-Hodgkin lymphomas (T-NHL), 3 B-NHL not otherwise specified (B-NHL NOS), 3 B acute lymphoblastic leukemias (B-ALL), and in 56 multiple myelomas (MM) by flow cytometry.

RESULTS

Positive (≥ 20%) expression of CD66abce clone Kat4c was detected in 76% of B-CLL and 76.8% of MM. The highest number of CD66abce-positive samples was in MCL and LPL (96.4% of 28 and 91.7% of 12 patients, respectively). Expression of CD66b clone BW 250/183 was examined in 114 of 260 samples. Positive expression was detected in 23.3% of B-CLL (6/35), 17.1% of MM (7/30), and 21.4% of MCL (3/14) samples.

CONCLUSION

The expression of CD66b compared to CD66abce was lower in all measured samples. Use of radiolabeled anti-CD66b antibody for the treatment of lymphoproliferative diseases appears to have limited preclinical substantiation.

CEACAM1: a key regulator of vascular permeability

Carcinoembryonic antigen cell adhesion molecule-1 (CEACAM1) is an immunoglobulin-like cell surface co-receptor expressed on epithelial, hematopoietic and endothelial cells. CEACAM1 functions as an adhesion molecule, mainly binding to itself or other members of the CEA family. We and others have previously shown that CEACAM1 is crucial for in vivo vascular integrity during ischemic neo-vascularization. Here, we have deciphered the roles of CEACAM1 in normal and pathological vascularization. We have found that Ceacam1−/− mice exhibit a significant increase in basal vascular permeability related to increased basal Akt and endothelial nitric oxide synthase (eNOS) activation in primary murine lung endothelial cells (MLECs). Moreover, CEACAM1 deletion in MLECs inhibits VEGF-mediated nitric oxide (NO) production, consistent with defective VEGF-dependent in vivo permeability in Ceacam1−/− mice. In addition, Ceacam1-null mice exhibit increased permeability of tumor vasculature. Finally, we demonstrate that CEACAM1 is tyrosine-phosphorylated upon VEGF treatment in a SHP-1- and Src-dependent manner, and that the key residues of the long cytoplasmic domain of CEACAM1 are crucial for CEACAM1 phosphorylation and NO production. This data represents the first report, to our knowledge, of a functional link between CEACAM1 and the VEGFR2/Akt/eNOS-mediated vascular permeability pathway.

Carcinoembryonic antigen-related cell adhesion molecule-1 regulates granulopoiesis by inhibition of granulocyte colony-stimulating factor receptor

Although carcinoembryonic antigen-related cell adhesion molecule-1 (CEACAM1) is an activation marker for neutrophils and delays neutrophil apoptosis, the role of CEACAM1 in granulopoiesis and neutrophil-dependent host immune responses has not been investigated. CEACAM1 expression correlated with granulocytic differentiation, and Ceacam1(-/-) mice developed neutrophilia because of loss of the Src-homology-phosphatase-1 (SHP-1)-dependent inhibition of granulocyte colony-stimulating factor receptor (G-CSFR) signal transducer and activator of transcription (Stat3) pathway provided by CEACAM1. Moreover, Ceacam1(-/-) mice were hypersensitive to Listeria Monocytogenes (LM) infection with an accelerated mortality. Reintroduction of CEACAM1 into Ceacam1(-/-) bone marrow restored normal granulopoiesis and host sensitivity to LM infection, while mutation of its immunoreceptor tyrosine-based inhibitory motifs (ITIMs) abrogated this restoration. shRNA-mediated reduction of Stat3 amounts rescued normal granulopoiesis, attenuating host sensitivity to LM infection in Ceacam1(-/-) mice. Thus, CEACAM1 acted as a coinhibitory receptor for G-CSFR regulating granulopoiesis and host innate immune response to bacterial infections.

SHP-1 in T cells limits the production of CD8 effector cells without impacting the formation of long-lived central memory cells

During responses against viruses and malignancies, naive CD8 T lymphocytes expand to form both short-lived effector cells and a population containing cells with the potential to be long-lived and participate in memory responses (memory precursor effector cells). The strength of antigenic, costimulatory, and cytokine signals during responses impacts the magnitude and type of CD8 populations formed. In vitro studies have revealed that the tyrosine phosphatase Src homology region 2 domain-containing phosphatase-1 (SHP-1) regulates signal transduction from receptors on T cells including the TCR, helping set the activation threshold, and therefore may shape responses of mature CD8 T cells in vivo. Analysis of CD8 T cells from motheaten mice, which are globally deficient in SHP-1, proved problematic due to cell-extrinsic effects of SHP-1 deficiency in non-T cells on CD8 T cells. Therefore, a conditional knockout of SHP-1 in mature single-positive T cells was developed to analyze cell-intrinsic consequences of complete and partial SHP-1 deficiency on CD8 T cell responses to acute viral infection. The results demonstrated that SHP-1 has disparate effects on subpopulations of responding cells, limiting the magnitude and quality of primary and secondary responses by reducing the number of short-lived effector cells generated without affecting the size of the memory precursor effector cell pool that leads to formation of long-term memory.

Generation of human CEACAM1 transgenic mice and binding of Neisseria Opa protein to their neutrophils

BACKGROUND

Human CEACAM1 is a cell-cell adhesion molecule with multiple functions including insulin clearance in the liver, vasculogenesis in endothelial cells, lumen formation in the mammary gland, and binding of certain human pathogens.

PRINCIPAL FINDINGS

Three genomic BAC clones containing the human CEACAM1 gene were microinjected into pronuclei of fertilized FVB mouse oocytes. The embryos were implanted in the oviducts of pseudopregnant females and allowed to develop to term. DNA from newborn mice was evaluated by PCR for the presence of the human CEACAM1 gene. Feces of the PCR positive offspring screened for expression of human CEACAM1. Using this assay, one out of five PCR positive lines was positive for human CEACAM1 expression and showed stable transmission to the F1 generation with the expected transmission frequency (0.5) for heterozygotes. Liver, lung, intestine, kidney, mammary gland, and prostate were strongly positive for the dual expression of both murine and human CEACAM1 and mimic that seen in human tissue. Peripheral blood and bone marrow granulocytes stained strongly for human CEACAM1 and bound Neisseria Opa proteins similar to that in human neutrophils.

CONCLUSION

These transgenic animals may serve as a model for the binding of human pathogens to human CEACAM1.