To be or not to be B7

Antibodies Targeting Human or Mouse VSIG4 Repolarize Tumor-Associated Macrophages Providing the Potential of Potent and Specific Clinical Anti-Tumor Response Induced across Multiple Cancer Types

V-set immunoglobulin domain-containing 4 (VSIG4) is a B7 family protein with known roles as a C3 fragment complement receptor involved in pathogen clearance and a negative regulator of T cell activation by an undetermined mechanism. VSIG4 expression is specific for tumor-associated and select tissue-resident macrophages. Increased expression of VSIG4 has been associated with worse survival in multiple cancer indications. Based upon computational analysis of transcript data across thousands of tumor and normal tissue samples, we hypothesized that VSIG4 has an important role in promoting M2-like immune suppressive macrophages and that targeting VSIG4 could relieve VSIG4-mediated macrophage suppression by repolarizing tumor-associated macrophages (TAMs) to an inflammatory phenotype. We have also observed a cancer-specific pattern of VSIG4 isoform distribution, implying a change in the functional regulation in cancer. Through a series of in vitro, in vivo, and ex vivo assays we demonstrate that anti-VSIG4 antibodies repolarize M2 macrophages and induce an immune response culminating in T cell activation. Anti-VSIG4 antibodies induce pro-inflammatory cytokines in M-CSF plus IL-10-driven human monocyte-derived M2c macrophages. Across patient-derived tumor samples from multiple tumor types, anti-VSIG4 treatment resulted in the upregulation of cytokines associated with TAM repolarization and T cell activation and chemokines involved in immune cell recruitment. VSIG4 blockade is also efficacious in a syngeneic mouse model as monotherapy as it enhances efficacy in combination with anti-PD-1, and the effect is dependent on the systemic availability of CD8+ T cells. Thus, VSIG4 represents a promising new target capable of triggering an anti-cancer response via multiple key immune mechanisms.

The Complement System in Kidney Transplantation

Kidney transplantation is the therapy of choice for patients who suffer from end-stage renal diseases. Despite improvements in surgical techniques and immunosuppressive treatments, long-term graft survival remains a challenge. A large body of evidence documented that the complement cascade, a part of the innate immune system, plays a crucial role in the deleterious inflammatory reactions that occur during the transplantation process, such as brain or cardiac death of the donor and ischaemia/reperfusion injury. In addition, the complement system also modulates the responses of T cells and B cells to alloantigens, thus playing a crucial role in cellular as well as humoral responses to the allograft, which lead to damage to the transplanted kidney. Since several drugs that are capable of inhibiting complement activation at various stages of the complement cascade are emerging and being developed, we will discuss how these novel therapies could have potential applications in ameliorating outcomes in kidney transplantations by preventing the deleterious effects of ischaemia/reperfusion injury, modulating the adaptive immune response, and treating antibody-mediated rejection.

The biology of VSIG4: Implications for the treatment of immune-mediated inflammatory diseases and cancer

V-set and immunoglobulin domain containing 4 (VSIG4), a type I transmembrane receptor exclusively expressed in a subset of tissue-resident macrophages, plays a pivotal role in clearing C3-opsonized pathogens and their byproducts from the circulation. VSIG4 maintains immune homeostasis by suppressing the activation of complement pathways or T cells and inducing regulatory T-cell differentiation, thereby inhibiting the development of immune-mediated inflammatory diseases but enhancing cancer progression. Consequently, VSIG4 exhibits a potential therapeutic effect for immune-mediated inflammatory diseases, but also is regarded as a novel target of immune checkpoint inhibition in cancer therapy. Recently, soluble VSIG4, the extracellular domain of VSIG4, shed from the surface of macrophages, has been found to be a biomarker to define macrophage activation-related diseases. This review mainly summarizes recent new findings of VSIG4 in macrophage phagocytosis and immune homeostasis, and discusses its potential diagnostic and therapeutic usage in infection, inflammation, and cancer.

Nanobodies for Medical Imaging: About Ready for Prime Time?

Recent advances in medical treatments have been revolutionary in shaping the management and treatment landscape of patients, notably cancer patients. Over the last decade, patients with diverse forms of locally advanced or metastatic cancer, such as melanoma, lung cancers, and many blood-borne malignancies, have seen their life expectancies increasing significantly. Notwithstanding these encouraging results, the present-day struggle with these treatments concerns patients who remain largely unresponsive, as well as those who experience severely toxic side effects. Gaining deeper insight into the cellular and molecular mechanisms underlying these variable responses will bring us closer to developing more effective therapeutics. To assess these mechanisms, non-invasive imaging techniques provide valuable whole-body information with precise targeting. An example of such is immuno-PET (Positron Emission Tomography), which employs radiolabeled antibodies to detect specific molecules of interest. Nanobodies, as the smallest derived antibody fragments, boast ideal characteristics for this purpose and have thus been used extensively in preclinical models and, more recently, in clinical early-stage studies as well. Their merit stems from their high affinity and specificity towards a target, among other factors. Furthermore, their small size (~14 kDa) allows them to easily disperse through the bloodstream and reach tissues in a reliable and uniform manner. In this review, we will discuss the powerful imaging potential of nanobodies, primarily through the lens of imaging malignant tumors but also touching upon their capability to image a broader variety of nonmalignant diseases.

Human Dendritic Cells Express the Complement Receptor Immunoglobulin Which Regulates T Cell Responses

The B7 family-related protein V-set and Ig containing 4 (VSIG4), also known as Z39Ig and Complement Immunoglobulin Receptor (CRIg), is the most recent of the complement receptors to be identified, with substantially distinct properties from the classical complement receptors. The receptor displays both phagocytosis-promoting and anti-inflammatory properties. The receptor has been reported to be exclusively expressed in macrophages. We now present evidence, that CRIg is also expressed in human monocyte-derived dendritic cells (MDDC), including on the cell surface, implicating its role in adaptive immunity. Three CRIg transcripts were detected and by Western blotting analysis both the known Long (L) and Short (S) forms were prominent but we also identified another form running between these two. Cytokines regulated the expression of CRIg on dendritic cells, leading to its up- or down regulation. Furthermore, the steroid dexamethasone markedly upregulated CRIg expression, and in co-culture experiments, the dexamethasone conditioned dendritic cells caused significant inhibition of the phytohemagglutinin-induced and alloantigen-induced T cell proliferation responses. In the alloantigen-induced response the production of IFNγ, TNF-α, IL-13, IL-4, and TGF-β1, were also significantly reduced in cultures with dexamethasone-treated DCs. Under these conditions dexamethasone conditioned DCs did not increase the percentage of regulatory T cells (Treg). Interestingly, this suppression could be overcome by the addition of an anti-CRIg monoclonal antibody to the cultures. Thus, CRIg expression may be a control point in dendritic cell function through which drugs and inflammatory mediators may exert their tolerogenic- or immunogenic-promoting effects on dendritic cells.

The Significance of VSIG4 Expression in Ovarian Cancer

OBJECTIVES

The protein V-set and Ig domain-containing 4 (VSIG4), a novel B7 family-related macrophage protein with the capacity to inhibit T-cell activation, has a potential role in cancer. Here we suggest its possibility as a therapeutic target and prognostic biomarker of ovarian cancer.

METHODS

Between January 2011 and June 2015, tumor tissues and peripheral blood samples were obtained during surgery from 10 patients with benign ovarian tumors and 22 patients with ovarian cancers. Messenger RNA and protein expression levels of VSIG4 in benign tumor and cancer tissues were examined by the reverse transcription polymerase chain reaction and Western blot, respectively. Soluble VSIG4 concentrations were measured by an enzyme-linked immunosorbent assay. The correlation between VSIG4 expression and the prognosis of ovarian cancer was analyzed according to the patients' clinicopathologic characteristics.

RESULTS

VSIG4 messenger RNA and protein expression levels in ovarian cancer tissues were higher than those in benign ovarian tumors (P = 0.0013 and 0.0001, respectively). Soluble VSIG4 concentrations were increased in patients with ovarian cancer compared with that in patients with benign ovarian tumors (P = 0.0452). Moreover, soluble VSIG4 levels were significantly increased in advanced-stage and recurrent ovarian cancer (P = 0.0244 and 0.0288, respectively). High VSIG4 expression of cancer tissue and low VSIG4 expression of plasma (soluble VSIG4) were associated with a longer disease-free interval (P = 0.0246 and 0.0398, respectively).

CONCLUSIONS

VSIG4 is overexpressed in ovarian cancers compared with that in benign tumors. This finding supports VSIG4 being used as a potential therapeutic target for ovarian cancer. Furthermore, soluble VSIG4 levels are associated with the progression and recurrence of ovarian cancer, indicating that soluble VSIG4 may be used as a potential biomarker for predicting tumor prognosis.

VSIG4 inhibits proinflammatory macrophage activation by reprogramming mitochondrial pyruvate metabolism

Exacerbation of macrophage-mediated inflammation contributes to pathogenesis of various inflammatory diseases, but the immunometabolic programs underlying regulation of macrophage activation are unclear. Here we show that V-set immunoglobulin-domain-containing 4 (VSIG4), a B7 family-related protein that is expressed by resting macrophages, inhibits macrophage activation in response to lipopolysaccharide. Vsig4 ^-/- mice are susceptible to high-fat diet-caused obesity and murine hepatitis virus strain-3 (MHV-3)-induced fulminant hepatitis due to excessive macrophage-dependent inflammation. VSIG4 activates the PI3K/Akt-STAT3 pathway, leading to pyruvate dehydrogenase kinase-2 (PDK2) upregulation and subsequent phosphorylation of pyruvate dehydrogenase, which results in reduction in pyruvate/acetyl-CoA conversion, mitochondrial reactive oxygen species secretion, and macrophage inhibition. Conversely, interruption of Vsig4 or Pdk2 promotes inflammation. Forced expression of Vsig4 in mice ameliorates MHV-3-induced viral fulminant hepatitis. These data show that VSIG4 negatively regulates macrophage activation by reprogramming mitochondrial pyruvate metabolism.

Molecular Imaging with Kupffer Cell-Targeting Nanobodies for Diagnosis and Prognosis in Mouse Models of Liver Pathogenesis

PURPOSE

Kupffer cells (KCs), the liver resident macrophages, are important mediators of tissue homeostasis and pathogen clearance. However, depending on the inflammatory stimuli, KCs have been involved in divergent hepato-protective or hepato-destructive immune responses. The versatility of KCs in response to environmental triggers, in combination with the specific biomarkers they express, make these macrophages attractive in vivo targets for non-invasive monitoring of liver inflammation or pathogenicity. This study aims to determine whether V-set and Ig domain-containing 4 (Vsig4) and C-type lectin domain family (Clec) 4, member F (Clec4F) can be used as imaging biomarkers for non-invasive monitoring of KCs during distinct liver inflammation models.

PROCEDURE

Flow cytometry (FACS), immuno-histochemistry (IHC), and single-photon emission computed tomography (SPECT) with Tc-99m labeled anti-Vsig4 or anti-Clec4F nanobodies (Nbs) was performed to evaluate in mice KC dynamics in concanavalin A (ConA)-induced hepatitis and in non-alcoholic steatohepatitis induced via methionine choline deficiency (MCD).

RESULTS

In homeostatic mice, Nbs targeting Clec4F were found to accumulate and co-localize with Vsig4-targeting Nbs only in the liver. Upon induction of acute hepatitis using ConA, down-regulation of the in vivo Nb imaging signal was observed, reflecting reduction in KC numbers as confirmed by FACS and IHC. On the other hand, induction of steatohepatitis resulted in higher signals in the liver corresponding to higher density of KCs. The Nb-imaging signals returned to normal levels after resolution of the investigated liver diseases.

CONCLUSIONS

Anti-Clec4F and anti-Vsig4 Nbs targeting KCs as molecular imaging biomarkers could allow non-invasive monitoring/staging of liver pathogenesis.

Structural evaluation of a nanobody targeting complement receptor Vsig4 and its cross reactivity

Vsig4 is a recently identified immune regulatory protein related to the B7 family with dual functionality: a negative regulator of T cell activation and a receptor for the complement components C3b and C3c. Here we present a structural evaluation of a nanobody, Nb119, against the extracellular IgV domain protein of both mouse and human recombinant Vsig4, which have a high degree of sequence identity. Although mouse and human Vsig4 bind to Nb119 with a 250 times difference in dissociation constants, the interaction results in a highly identical assembly with a RMSD of 0.4Å. The molecular determinants for Vsig4 recognition and cross reactivity unveiled by the atomic structure of Nb119 in complex with mVsig4 and hVsig4 afford new insights useful for the further optimization of the nanobody for potential use in humans. Additionally, structural analysis of the Vsig4-Nb119 complexes indicates that Nb119 occupies the interface on Vsig4 recognized by the macroglobulin-like domains MG4 and MG5 of C3b. Thus an affinity-improved Nb119 may have the potential to influence the activation of both T cells and complement.

Endogenous VSIG4 negatively regulates the helper T cell-mediated antibody response

VSIG4 acts as a co-inhibitory ligand to negatively regulate T cell proliferation and cytokine production, and its expression is restricted to macrophages. We hypothesized that endogenous VSIG4 impairs helper T cell functions and then inhibits the subsequent antibody response. Isotype switching of ovalbumin (OVA)-specific antibody subclasses to IgG1, IgG2a, IgG2b, and IgG3 was enhanced in OVA-immunized VSIG4 knockout (KO) mice. 2,4,6-Trinitrophenyl hapten (TNP) - Keyhole Limpet Hemocyanin (KLH)-primed B cells cocultured with OVA-primed CD4(+) T cells from OVA-immunized VSIG4 KO mice in the presence of TNP-OVA showed enhanced isotype switching to IgG subclasses compared to those cocultured with cells isolated from OVA-immunized wild-type (WT) mice. Furthermore, the levels of CD40L expression, the frequency of memory CD4(+) T cells, and the production of isotype switching-inducing cytokines increased significantly in OVA-primed CD4(+) T cells from VSIG4 KO mice. T cells from OVA-specific T cell receptor (TCR) transgenic mice produced more IFN-γ when cocultured with macrophages from VSIG4 KO mice compared to WT mice. Thus, our results demonstrate that macrophage-associated VSIG4 plays a negative role in helper T cell-dependent isotype switching by inhibiting helper T cell activation and differentiation, and suppressing the isotype switching-inducing cytokine production in antigen-primed CD4(+) helper T cells.

Protein kinase cα regulates the expression of complement receptor Ig in human monocyte-derived macrophages

The complement receptor Ig (CRIg) is selectively expressed by macrophages. This receptor not only promotes the rapid phagocytosis of bacteria by macrophages but also has anti-inflammatory and immunosuppressive functions. Previous findings have suggested that protein kinase C (PKC) may be involved in the regulation of CRIg expression in human macrophages. We have now examined the role of PKCα in CRIg expression in human monocyte-derived macrophages (MDM). Macrophages nucleofected with plasmid containing short hairpin RNA against PKCα showed markedly reduced expression of PKCα, but normal PKCζ expression, by Western blotting analysis, and vice versa. PKCα-deficient MDM showed increased expression of CRIg mRNA and protein (both the long and short form), an increase in phagocytosis of complement-opsonized Candida albicans, and decreased production of TNF-α and IL-6. TNF-α caused a marked decrease in CRIg expression, and addition of anti-TNF mAb to the TNF-α-producing MDMs increased CRIg expression. PKCα-deficient macrophages also showed significantly less bacterial LPS-induced downregulation of CRIg. In contrast, cells deficient in PKCα showed decreased expression of CR type 3 (CR3) and decreased production of TNF-α and IL-6 in response to LPS. MDM developed under conditions that increased expression of CRIg over CR3 showed significantly reduced production of TNF-α in response to opsonized C. albicans. The findings indicate that PKCα promotes the downregulation of CRIg and upregulation of CR3 expression and TNF-α and IL-6 production, a mechanism that may promote inflammation.

Costimulatory molecule VSIG4 exclusively expressed on macrophages alleviates renal tubulointerstitial injury in VSIG4 KO mice

BACKGROUND

Activation and infiltration of T cells and macrophages are key features of renal tubulointerstitial injury. The costimulatory molecule V-set and immunoglobulin domain-containing protein-4 (VSIG4), which is exclusively expressed on macrophages, is capable of inhibiting the T cell response. However, it is unclear whether VSIG4 is involved in renal tubulointerstitial injury. This study was designed to investigate the role of VSIG4 in renal tubulointerstitial injury and the related T cell infiltration.

METHODS

The unilateral ureteric obstruction (UUO) model of renal inflammation and tubulointerstitial fibrosis was established in VSIG4 transgenic knock-out C57BL/6 mice (VSIG4(-/-)) and wild-type C57BL/6 mice (VSIG4(+/+)). Comparative analysis of renal biological indices were assessed by quantitative real-time PCR and immunofluorescence staining.

RESULTS

Both the VSIG4(-/-) and VSIG4(+/+) mice showed UUO-related temporal changes in renal expression of CD3, CD4 and CD8 T cell markers, with the protein levels being significantly lower in the VSIG4(+/+) UUO mice. Moreover, at each time point examined the UUO VSIG4(+/+) mice showed significantly lower renal mRNA levels of the cytokines interleukin (IL)-2, interferon- and tumor necrosis factor-, but significantly higher IL-10, than the UUO VSIG4(-/-) mice.

CONCLUSIONS

The macrophage-expressed VSIG4 may act to alleviate renal tubulointerstitial injury via inhibition of T cell infiltration and secretion of inflammation related factors.

Recent advancements in cytotoxic T lymphocyte generation methods using carbohydrate-coated liposomes

Both tumor-specific CD4⁺ and CD8⁺ T cells have been identified, and the latter is known as a major effector of adaptive antitumor immune responses. Optimal antitumor immune responses are considered to require the concomitant activation of both CD8⁺ and CD4⁺ T cells and the additional selective activation of CD4⁺ T cells with helper, but not regulatory function. As optimal antitumor immune responses are generated by the concomitant activation of both T cell types, it is necessary for vaccine methods involving cytotoxic T-lymphocytes (CTLs) generation to possess a mechanism whereby antigen presenting cells can present administrated exogenous antigens on not only Major histocompatibility complex (MHC) class II, but also MHC class I molecules.

The low expression of CD80 correlated with the vascular endothelial growth factor in esophageal cancer tissue

AIMS

To analyze the mRNA and protein expression of CD80 and vascular endothelial growth factor (VEGF) in esophageal cancer (EC) tissue, investigate the causes of esophageal cancer cell escape from immune surveillance.

METHODS

We detected the CD80 and VEGF mRNA with reverse transcription polymerase chain reaction (RT-PCR), CD80 protein with flow cytometry, VEGF protein with immunohistochemistry in the cancer tissues in 118 EC patients, and the normal esophageal tissue as controls.

RESULTS

The expression of CD80 mRNA and protein in cancer tissues were lower than that in the controls (p<0.01, respectively), The CD80 protein expression in poor differentiation was lower than that in the well and moderate (P<0.01), in the patients with lymph node metastasis lower than that with no metastasis (P=0.01), in stage IIIA patients lower than that in stages I and II patients (P=0.04); the VEGF mRNA and protein expression were just right opposite. The mean survival time in the CD80 positive group was significantly longer than that in the negative (p=0.041); while in VEGF positive group was lower than that in the negative (p=0.046). The CD80 expression of mRNA and protein were correlated negatively with VEGF in the cancer tissues (r=-0.82, -0.87, respectively).

CONCLUSION

It is suggested that CD80 was impaired in the EC tissues and correlated with the clinicopathological characteristics and prognosis, which indicated the dysfunction of immune system and enhancing the progression of EC. The low expression of CD80 correlated with the overexpression of VEGF.

Cooperation between molecular targets of costimulation in promoting T cell persistence and tumor regression

Costimulation regulates multiple cellular processes of T cells inducing proliferation, expansion, and survival. The molecular targets of costimulation might then be useful to augment T cell activities. Two defined targets of costimulatory signals in primary T cells are the anti-apoptotic bcl-2 family molecule Bcl-x(L), and survivin, an inhibitor of apoptosis family member that might regulate both cell division and survival. However, the relative importance of, and relationship between, these molecules in primary T cells is not clear. To understand whether they have overlapping or cooperative functions, we used retrovirus-mediated transduction to introduce Bcl-x(L) and survivin separately, or together linked by a 2A picornavirus self-cleaving peptide, into Ag-responding CD8(+) T cells. We found that CD8(+) effector T cells expressing both Bcl-x(L) and survivin strongly expanded at an early stage and had a long-term survival advantage over cells transduced with either molecule alone. In vivo, with response to tumor-expressed Ag following adoptive T cell transfer, Ag-reactive CD8(+) T cells expressing both Bcl-x(L) and survivin displayed greatly enhanced tumor protective activity compared with CD8(+) T cells expressing either molecule introduced separately. These results indicate that Bcl-x(L) and survivin can critically contribute in a cooperative, nonredundant manner to augment the accumulation and persistence of CD8(+) T cells following encounter with Ag. The data provide new insights into why costimulatory signals might need to be sustained over time and suggest a potential novel approach to augment cellular immunotherapy for cancer.

A role of macrophage complement receptor CRIg in immune clearance and inflammation

Complement receptor of the immunoglobulin superfamily (CRIg), also referred to as Z39Ig and V-set and Ig domain-containing 4 (VSIG4), has recently been implicated in the clearance of systemic pathogens and autologous cells. CRIg is exclusively expressed on tissue resident macrophages and binds to multimers of C3b and iC3b that are covalently attached to particle surfaces. Next to functioning as an important clearance receptor, CRIg's extracellular domain inhibits complement activation through the alternative, but not the classical, pathway, providing a novel tool to selectively block this pathway in vivo. Here, we review a role for CRIg in immune clearance, T-cell responses and complement regulation, and discuss the implications for disease manifestation.

The B7 family and cancer therapy: costimulation and coinhibition

The activation and development of an adaptive immune response is initiated by the engagement of a T-cell antigen receptor by an antigenic peptide-MHC complex. The outcome of this engagement is determined by both positive and negative signals, costimulation and coinhibition, generated mainly by the interaction between the B7 family and their receptor CD28 family. The importance of costimulation and coinhibition of T cells in controlling immune responses is exploited by tumors as immune evasion pathways. Absence of the expression of costimulatory B7 molecules renders tumors invisible to the immune system, whereas enhanced expression of inhibitory B7 molecules protects them from effective T cell destruction. Therefore, the manipulation of these pathways is crucial for developing effective tumor immunotherapy. Translation of our basic knowledge of costimulation and coinhibition into early clinical trials has shown considerable promise.

Macrophage complement receptors and pathogen clearance

Phagocytosis, an important mechanism of the host-defence system and a primary function of macrophages, is facilitated by opsonization, a process by which serum components tag pathogens for recognition by neutrophils and macrophages. Complement component C3 is central to opsonization. Its first cleavage product, C3b, forms the multisubunit enzyme, C3bBb, which proteolytically cleaves additional C3 molecules on the pathogen surface. C3b is further degraded to iC3b, C3c and C3dg, products that serve as ligands for selective complement receptors on leukocytes. This receptor-ligand interaction subsequently modulates immune responses or directly targets the pathogen for clearance by phagocytosis. Although a central role for C3 in phagocytosis of certain pathogens is well accepted, the receptors orchestrating the phagocytic response have not been well characterized. The recent structures of C3 and its breakdown products have increased our insights into the molecular basis of complement activation and recognition by their receptors. Here we review the biology of macrophage receptors for C3 fragments and discuss their role in the host response to pathogens.