Label-free detection of prostaglandin transporter (SLCO2A1) function and inhibition: insights by wound healing and TRACT assays

The prostaglandin transporter (PGT, SLCO2A1) mediates transport of prostanoids (a.o. prostaglandin E2 (PGE2)) into cells and thereby promotes their degradation. Overexpression of PGT leads to low extracellular PGE2 levels and has been linked to impaired wound healing of diabetic foot ulcers. Inhibition of PGT could thus be beneficial, however, no PGT inhibitors are currently on the market and drug discovery efforts are hampered by lack of high-through screening assays for this transporter. Here we report on a label-free impedance-based assay for PGT that measures transport activity through receptor activation (TRACT) utilizing prostaglandin E2 receptor subtype EP3 and EP4 that are activated by PGE2. We found that induction of PGT expression on HEK293-JumpIn-SLCO2A1 cells that also express EP3 and EP4 leads to an over 10-fold reduction in agonistic potency of PGE2. PGE2 potency could be recovered upon inhibition of PGT-mediated PGE2 uptake with PGT inhibitors olmesartan and T26A, the potency of which could be established as well. Moreover, the TRACT assay enabled the assessment of transport function of PGT natural variants. Lastly, HUVEC cells endogenously expressing prostanoid receptors and PGT were exploited to study wound healing properties of PGE2 and T26A in real-time using a novel impedance-based scratch-induced wound healing assay. These novel impedance-based assays will advance PGT drug discovery efforts and pave the way for the development of PGT-based therapies.

Anti-carbamylated protein antibodies in systemic sclerosis

BACKGROUND

To investigate the presence of different isotypes of anti-carbamylated protein (CarP) antibodies in systemic sclerosis (SSc) patients and its association with skin involvement.

METHODS

Sera of 194 SSc patients from the Leiden CCISS cohort, fulfilling ACR/EULAR 2013 criteria and a clinical diagnosis of SSc, 83 patients with other connective tissue diseases/Raynaud's Phenomenon, 24 rheumatoid arthritis patients and 98 age and sex-matched healthy controls were tested for the presence of anti-CarP IgG, IgA and IgM, determined by ELISA. Clinical characteristics, that were evaluated in SSc patients, included age, anti-topoisomerase antibodies (ATA), anti-centromere antibodies (ACA) and modified Rodnan Skin Score (mRSS).

RESULTS

The SSc patients were 55 (SD:13) years and 155 (80%) were female. Forty-four (23%) patients tested positive for ATA, and 80 (42%) ACA. The median mRSS was 2 (range: 0; 47). Prevalence of anti-CarP IgG was higher in SSc patients than in healthy controls (8% vs 3%, p = 0.007. Prevalence of anti-CarP IgA and IgM and levels of anti-CarP isotypes were comparable between SSc patients and healthy controls. Fifteen (8%) SSc patients tested positive for anti-CarP IgG, 16 (8%) for anti-CarP IgA, and 36 (19%) for anti-CarP IgM. There were no significant correlations between age and levels of anti-CarP isotypes. No correlation between anti-CarP IgG levels and mRSS was found (r = 0.141, p = 0.049), nor for anti-CarP IgM and IgA levels. Anti-CarP IgA levels were higher in ATA compared to ACA positive SSc patients (ATA: 616 aU/ml [359; 1103]; ACA: 424 aU/ml [300; 673], p = 0.015).

CONCLUSION

SSc patients can test positive for Anti-CarP IgG, IgA and IgM. We do not observe a relevant clinical association between anti-CarP antibody response and skin involvement in SSc.

Anti-topoisomerase, but not anti-centromere B cell responses in systemic sclerosis display active, Ig-secreting cells associated with lung fibrosis

OBJECTIVES

Almost all patients with systemic sclerosis (SSc) harbour autoantibodies. Anti-topoisomerase antibodies (ATA) and anti-centromere antibodies (ACA) are most prevalent and associate with distinct clinical phenotypes. B cell responses underlying these phenotypes are ill-defined. To understand how B cell autoreactivity and disease pathology connect, we determined phenotypic and functional characteristics of autoreactive B cells in ATA-positive and ACA-positive patients.

METHODS

Levels and isotypes of autoantibodies secreted by ex vivo cultured peripheral blood mononuclear cells from patients with ATA-positive (n=22) and ACA-positive (n=20) SSc were determined. Antibody secreting cells (ASCs) were isolated by cell sorting and cultured separately. Correlations were studied between the degree of spontaneous autoantibody production and the presence and degree of interstitial lung disease (ILD).

RESULTS

Circulating B cells secreting either ATA-immunoglobulin G (IgG) or ACA-IgG on stimulation was readily detectable in patients. The ATA response, but not the ACA response, showed additional secretion of autoreactive IgA. ATA-IgG and ATA-IgA were also secreted spontaneously. Additional cell sorting confirmed the presence of ATA-secreting plasmablasts. The degree of spontaneous ATA-secretion was higher in patients with ILD than in those without (p<0.001) and correlated with the degree of pulmonary fibrosis (p<0.001).

CONCLUSION

In contrast to ACA-positive patients, ATA-positive patients show signs of recent activation of the B cell response that hallmarks this disease. The degree of activation correlates with the presence and severity of ILD, the most deleterious disease manifestation. This could explain differential responsiveness to B cell depleting therapy. The abundant and spontaneous secretion of ATA-IgG and ATA-IgA may point toward a continuously activating trigger.

Progression from suspected to definite systemic sclerosis and the role of anti-topoisomerase I antibodies

INTRODUCTION

Early diagnosis of systemic sclerosis (SSc) is important to start therapeutic interventions timely. Important risk factors for progression to SSc are the SSc-specific autoantibodies, of whom anti-centromere antibodies (ACA) and anti-topoisomerase I antibodies (ATA) are the most frequent. ATA is associated with a severe disease course. A more detailed characterisation of the ATA-response in SSc might increase insights in preclinical disease stages and improve prognostication. To address this we identified all patients with suspected very early ATA-positive SSc, defined as all patients who are ATA-positive not fulfilling American College of Rheumatology (ACR)/European Alliance of Associations for Rheumatology (EULAR) 2013 criteria, in the Leiden Combined Care in Systemic Sclerosis (CCISS)-cohort and found very low numbers.

METHODS

This triggered us to search the literature on the ATA prevalence in patients with suspected very early SSc and contribution of the SSc-specific autoantibodies to progression from suspected very early to definite SSc. To increase insights on the ATA-response in suspected very early SSc, we then evaluated the association between the ATA-response and time between onset of Raynaud's phenomenon (RP) and first non-RP symptom, as a proxy for progressing to definite SSc, in all patients with ATA-positive SSc from the Leiden CCISS-cohort.

RESULTS

In short, included studies show that prevalence of ATA is much lower in suspected very early SSc than in populations fulfilling ACR/EULAR 2013 criteria. After 1-15 years of follow-up, only 52% of the patients with suspected very early SSc progress to definite SSc. ATA-IgG levels tend to be higher in patients with ATA-positive SSc with more rapid disease progression.

CONCLUSION

Although a role of ATA in disease progression is suggested, more studies on the ATA response in suspected very early SSc are warranted.

Association Between Centromere- and Topoisomerase-specific Immune Responses and the Degree of Microangiopathy in Systemic Sclerosis

OBJECTIVE

Autoreactive antibody responses, including the use of several isotypes of autoantibodies, have been shown to be associated with clinical outcome in several rheumatic autoimmune diseases. The goals of this study were to evaluate whether (1) anticentromere antibody (ACA)- and antitopoisomerase antibody (ATA)-specific isotype expression, and (2) organ involvement are associated with the degree of microangiopathy in systemic sclerosis (SSc).

METHODS

ACA and ATA IgG, IgM, and IgA levels were measured in baseline serum samples of ACA IgG-positive (+) and ATA IgG+ patients with SSc. The degree of microangiopathy was determined based on nailfold videocapillaroscopy (NVC) images collected at the same point in time. Logistic regression analyses with autoantibodies, clinical characteristics, isotype expression, and ACA and ATA IgG, IgM, and IgA levels as independent variables, and NVC pattern as the dependent variable were performed.

RESULTS

In 164 patients, isotype levels and degree of microangiopathy were evaluated. Logistic regression confirmed the association of the degree of microangiopathy with the presence of digital ulcers (OR 3.07, 95% CI 1.43-6.60), interstitial lung disease (OR 3.41, 95% CI 1.11-10.61), and pulmonary arterial hypertension (OR 5.58, 95% CI 2.05-17.81). ATA positivity was associated with more severe microangiopathy (OR 2.09, 95% CI 1.05-4.13). Patients who expressed solely ACA IgG showed a trend towards less severe microangiopathy compared to patients also expressing ACA IgM and/or IgA. Levels of ACA IgG and ATA IgM were found to be associated with microangiopathy severity.

CONCLUSION

We observed an association between ACA and ATA responses and the degree of microangiopathy in SSc. These findings might indicate that the breadth of the autoimmune response, as reflected by autoantibody production and microvascular damage, interacts in the pathophysiology of SSc.

APRIL Induces a Novel Subset of IgA+ Regulatory B Cells That Suppress Inflammation via Expression of IL-10 and PD-L1

Regulatory B cells (Bregs) are immunosuppressive cells that modulate immune responses through multiple mechanisms. The signals required for the differentiation and activation of these cells remain still poorly understood. We have already shown that overexpression of A PRoliferation-Inducing Ligand (APRIL) reduces the incidence and severity of collagen-induced arthritis (CIA) in mice. Furthermore, we have described that APRIL, but not BAFF, promoted IL-10 production and regulatory functions in human B cells. Therefore, we hypothesized that APRIL, but not BAFF, may be involved in the induction and/or activation of IL-10 producing Bregs that suppress inflammatory responses in vitro and in vivo. Here, we describe that APRIL promotes the differentiation of naïve human B cells to IL-10-producing IgA⁺ B cells. These APRIL-induced IgA⁺ B cells display a Breg phenotype and inhibit T cell and macrophage responses through IL-10 and PD-L1. Moreover, APRIL-induced IL-10 producing Bregs suppress inflammation in vivo in experimental autoimmune encephalitis (EAE) and contact hypersensitivity (CHS) models. Finally, we showed a strong correlation between APRIL and IL-10 in the inflamed synovial tissue of inflammatory arthritis patients. Collectively, these observations indicate the potential relevance of this novel APRIL-induced IgA⁺ Breg population for immune homeostasis and immunopathology.

Anti-citrullinated protein antibody response after primary EBV infection in kidney transplant patients

Rheumatoid arthritis (RA) is a chronic inflammatory disease of synovial joints, characterized by the presence of the highly disease-specific anti-citrullinated protein antibodies (ACPA) in approximately 70% of patients. Epstein-Barr virus (EBV) has previously been suggested to be involved in the pathophysiology of RA. However, given the high incidence of EBV in the general population and the difficulty of detecting initial infection, providing a direct link between EBV infection and RA development has remained elusive. We hypothesized that primary EBV infection may be a trigger for the development of the ACPA response in vivo. Using a unique cohort of 26 kidney transplant patients with a primary EBV infection, the presence of ACPA before and following infection was determined. No increase in IgG anti-CCP2 titers was detected following EBV infection. IgG anti-CCP2 antibodies were present in two patients and borderline positive in another. These three patients were HLA-DR4 negative. To test whether EBV infection may trigger a non-class switched anti-CCP2 response, IgM anti-CCP2 antibodies were analyzed. No general trend in the IgM anti-CCP2 response was observed following EBV infection. Since two out of the three IgG anti-CCP2 (borderline) positive patients were diagnosed with IgA nephropathy, 23 additional IgA nephropathy patients were tested for IgG anti-CCP2, regardless of their EBV status. All of these patients were IgG anti-CCP2 negative, indicating that IgG anti-CCP2 is not commonly present in IgA nephropathy patients. Collectively, these data do not support the hypothesis that EBV does trigger the highly RA specific ACPA response.

Langerin-mediated internalization of a modified peptide routes antigens to early endosomes and enhances cross-presentation by human Langerhans cells

The potential of the skin immune system to generate immune responses is well established, and the skin is actively exploited as a vaccination site. Human skin contains several antigen-presenting cell subsets with specialized functions. In particular, the capacity to cross-present exogenous antigens to CD8+ T cells is of interest for the design of effective immunotherapies against viruses or cancer. Here, we show that primary human Langerhans cells (LCs) were able to cross-present a synthetic long peptide (SLP) to CD8⁺ T cells. In addition, modification of this SLP using antibodies against the receptor langerin, but not dectin-1, further enhanced the cross-presenting capacity of LCs through routing of internalized antigens to less proteolytic early endosome antigen 1⁺ early endosomes. The potency of LCs to enhance CD8⁺ T-cell responses could be further increased through activation of LCs with the toll-like receptor 3 ligand polyinosinic:polycytidylic acid (pI:C). Altogether, the data provide evidence that human LCs are able to cross-present antigens after langerin-mediated internalization. Furthermore, the potential for antigen modification to target LCs specifically provides a rationale for generating effective anti-tumor or anti-viral cytotoxic T lymphocyte responses.

Cross-presentation through langerin and DC-SIGN targeting requires different formulations of glycan-modified antigens

Dendritic cells (DCs) and Langerhans cells (LC) are professional antigen presenting cells (APCs) that initiate humoral and cellular immune responses. Targeted delivery of antigen towards DC- or LC-specific receptors enhances vaccine efficacy. In this study, we compared the efficiency of glycan-based antigen targeting to both the human DC-specific C-type lectin receptor (CLR) DC-SIGN and the LC-specific CLR langerin. Since DC-SIGN and langerin are able to recognize the difucosylated oligosaccharide Lewis Y (Le(Y)), we prepared neoglycoconjugates bearing this glycan epitope to allow targeting of both lectins. Le(Y)-modified liposomes, with an approximate diameter of 200nm, were significantly endocytosed by DC-SIGN(+) DCs and mediated efficient antigen presentation to CD4(+) and CD8(+) T cells. Surprisingly, although langerin bound to Le(Y)-modified liposomes, LCs exposed to Le(Y)-modified liposomes could not endocytose liposomes nor mediate antigen presentation to T cells. However, LCs mediated an enhanced cross-presentation when antigen was delivered through langerin using Le(Y)-modified synthetic long peptides. In contrast, Le(Y)-modified synthetic long peptides were recognized by DC-SIGN, but did not trigger antigen internalization nor antigen cross-presentation. These data demonstrate that langerin and DC-SIGN have different size requirements for antigen uptake. Although using glycans remains an interesting option in the design of anti-cancer vaccines targeting multiple CLRs, aspects such as molecule size and conformation need to be taken in consideration.

Understanding the biology of antigen cross-presentation for the design of vaccines against cancer

Antigen cross-presentation, the process in which exogenous antigens are presented on MHC class I molecules, is crucial for the generation of effector CD8(+) T cell responses. Although multiple cell types are being described to be able to cross-present antigens, in vivo this task is mainly carried out by certain subsets of dendritic cells (DCs). Aspects such as the internalization route, the pathway of endocytic trafficking, and the simultaneous activation through pattern-recognition receptors have a determining influence in how antigens are handled for cross-presentation by DCs. In this review, we will summarize new insights in factors that affect antigen cross-presentation of human DC subsets, and we will discuss the possibilities to exploit antigen cross-presentation for immunotherapy against cancer.

Effects of antigen-expressing immunostimulatory liposomes on chemotaxis and maturation of dendritic cells in vitro and in human skin explants

PURPOSE

Antigen-Expressing Immunostimulatory Liposomes (AnExILs) represent a novel DNA vaccination platform based on the production of protein antigens from DNA templates inside liposomes mediated by an in vitro transcription and translation (IVTT) mix. The aim of this study was to analyze the effects of AnExILs on different dendritic cells (DCs) models and to better understand the role of the different components of this formulation on its adjuvanticity.

METHODS

The effect of β-galactosidase-expressing AnExILs on maturation and particle uptake by murine DC cell line, fresh human monocyte-derived DCs or human dermal DCs in skin explants was investigated and compared to the effects of either plain liposomes or IVTT mix alone.

RESULTS

AnExILs induced efficient DC chemotaxis and promoted up-regulation of maturation markers on murine DCs, due to the presence of IVTT in the formulation. Furthermore, the amount of active βGal associated with DCs was higher for AnExILs than for free βGal expressed in IVTT or βGal encapsulated into non-adjuvanted liposomes. Most interestingly, the same trend was observed with human DCs.

CONCLUSIONS

Both IVTT mix and liposomal vehicles were shown to be key components of the AnExIL formulation responsible for its adjuvanticity. AnExILs combine antigen production, adjuvanticity and delivery in one system, and can efficiently activate both murine and human DCs.

Skin-resident antigen-presenting cells: instruction manual for vaccine development

The induction of antigen-specific effector T cells is driven by proper antigen presentation and co-stimulation by dendritic cells (DCs). For this reason strategies have been developed to instruct DCs for the induction of CD4⁺ and CD8⁺ T cell responses. Since DCs are localized, amongst other locations, in peripheral tissues such as the skin, new vaccines are aiming at targeting antigens to DCs in situ. Optimal skin-DC targeting in combination with adequate adjuvant delivery facilitates DC maturation and migration to draining lymph nodes and enhances antigen cross-presentation and T cell priming. In this review we describe what DC subsets populate the human skin, as well as current vaccination strategies based on targeting strategies and alternative administration for the induction of robust long-lived anti-cancer effector T cells.

Glycan-modified liposomes boost CD4+ and CD8+ T-cell responses by targeting DC-SIGN on dendritic cells

Cancer immunotherapy requires potent tumor-specific CD8(+) and CD4(+) T-cell responses, initiated by dendritic cells (DCs). Tumor antigens can be specifically targeted to DCs in vivo by exploiting their expression of C-type lectin receptors (CLR), which bind carbohydrate structures on antigens, resulting in internalization and antigen presentation to T-cells. We explored the potential of glycan-modified liposomes to target antigens to DCs to boost murine and human T-cell responses. Since DC-SIGN is a CLR expressed on DCs, liposomes were modified with DC-SIGN-binding glycans Lewis (Le)(B) or Le(X). Glycan modification of liposomes resulted in increased binding and internalization by BMDCs expressing human DC-SIGN. In the presence of LPS, this led to 100-fold more efficient presentation of the encapsulated antigens to CD4(+) and CD8(+) T-cells compared to unmodified liposomes or soluble antigen. Similarly, incubation of human moDC with melanoma antigen MART-1-encapsulated liposomes coated with Le(X) in the presence of LPS led to enhanced antigen-presentation to MART-1-specific CD8(+) T-cell clones. Moreover, this formulation drove primary CD8(+) T-cells to differentiate into high numbers of tetramer-specific, IFN-γ-producing effector T-cells. Together, our data demonstrate the potency of a glycoliposome-based vaccine targeting DC-SIGN for CD4(+) and CD8(+) effector T-cell activation. This approach may offer improved options for treatment of cancer patients and opens the way to in situ DC-targeted vaccination.

Cross-talk between tumor and myeloid cells: how to tip the balance in favor of antitumor immunity

Myeloid differentiation is often disturbed in cancer, leading to reduced frequencies of immunostimulatory dendritic cells and an over-representation of immunosuppressive immature myeloid cells, granulocytes and macrophages. As a result of this skewed myeloid differentiation, a highly immunosuppressive myeloid subset becomes prevalent during cancer development; these myeloid-derived suppressor cells are also recruited as a collateral to certain protumorigenic inflammatory processes, resulting in an effective downregulation of T-cell-mediated immune surveillance and antitumor immunity. In this article, some of the important myeloid cell subsets and mediators involved in cancer-related immune suppression are reviewed. Furthermore, cross-talk between tumors and the myeloid compartment, and ways in which it can suppress effective cell-mediated immunity, are discussed, as well as possible therapeutic approaches to tip the balance in favor of antitumor immunity.