Human serum amyloid P component binds to peripheral blood monocytes

Evaluation of multiple immunoassay formats for detection of anti-drug antibodies to zinpentraxin alfa

Zinpentraxin alfa (rhPTX-2; PRM-151) is currently being developed for the treatment of fibrotic diseases such as idiopathic pulmonary fibrosis and myelofibrosis. Notably, because it is administered chronically and has an endogenously expressed counterpart, clinical studies of zinpentraxin alpha must include immunogenicity assessments. Since the typical homogenous bridging ELISA assay does not adequately measure anti-drug antibodies (ADAs) against zinpentraxin alfa, additional assay formats have been developed to evaluate immunogenicity of this therapeutic. Here, we present the evaluation of four distinct assay formats that were used to measure zinpentraxin alpha ADA: step-wise bridging, direct binding, total ADA, and the semi-homogeneous formats, based on multiple parameters including assay sensitivity, precision, and drug tolerance. This paper presents the full details of method development for each of the aforementioned assay formats including evaluation of sample pre-treatment, determination of cut point, and assessment of assay performance by analyzing a subset of clinical samples. Overall, the semi-homogenous ADA assay format with no sample pre-treatment was selected for the measurement of zinpentraxin alpha immunogenicity as it provided the desired sensitivity, drug tolerance, and reproducibility. Our study emphasizes the importance of assay format evaluation during drug development and the necessity to select the most suitable assay format and sample pre-treatment method by which to evaluate therapeutic drug immunogenicity.

Concerted application of LC-MS and ligand binding assays to better understand exposure of a large molecule drug

AIM

A ligand-binding assay (LBA) was used to measure exposure of PRM-151, the recombinant form of human pentraxin-2 (PTX-2), a complex pentamer with multiple binding partners. However, the assay showed a lack of dose-dependent exposure in select preclinical species and it could not differentiate the infused PRM-151 from the endogenous PTX-2 in nonhuman primates.

MATERIALS & METHODS

Instead of assessing interference from its multiple binding partners, which could be time consuming and laborious, a LC-MS assay avoid of these interference was implemented to measure 'total' drug without the use of immunoaffinity capture reagents.

RESULTS & CONCLUSION

The resultant LC-MS data confirmed the original data and the lack of dose-dependent exposure is now understood to be due to the multiple and diverse targets and functions and resultant complex biodistribution rather than an assay artifact.

Exploring the Immunomodulatory Moonlighting Activities of Acute Phase Proteins for Tolerogenic Dendritic Cell Generation

The acute phase response is generated by an overwhelming immune-inflammatory process against infection or tissue damage, and represents the initial response of the organism in an attempt to return to homeostasis. It is mediated by acute phase proteins (APPs), an assortment of highly conserved plasma reactants of seemingly different functions that, however, share a common protective role from injury. Recent studies have suggested a crosstalk between several APPs and the mononuclear phagocyte system (MPS) in the resolution of inflammation, to restore tissue integrity and function. In fact, monocyte-derived dendritic cells (Mo-DCs), an integral component of the MPS, play a fundamental role both in the regulation of antigen-specific adaptive responses and in the development of immunologic memory and tolerance, particularly in inflammatory settings. Due to their high plasticity, Mo-DCs can be modeled in vitro toward a tolerogenic phenotype for the treatment of aberrant immune-inflammatory conditions such as autoimmune diseases and allotransplantation, with the phenotypic outcome of these cells depending on the immunomodulatory agent employed. Yet, recent immunotherapy trials have emphasized the drawbacks and challenges facing tolerogenic Mo-DC generation for clinical use, such as reduced therapeutic efficacy and limited in vivo stability of the tolerogenic activity. In this review, we will underline the potential relevance and advantages of APPs for tolerogenic DC production with respect to currently employed immunomodulatory/immunosuppressant compounds. A further understanding of the mechanisms of action underlying the moonlighting immunomodulatory activities exhibited by several APPs over DCs could lead to more efficacious, safe, and stable protocols for precision tolerogenic immunotherapy.

Persistent lung inflammation and fibrosis in serum amyloid P component (APCs-/-) knockout mice

Fibrosing diseases, such as pulmonary fibrosis, cardiac fibrosis, myelofibrosis, liver fibrosis, and renal fibrosis are chronic and debilitating conditions and are an increasing burden for the healthcare system. Fibrosis involves the accumulation and differentiation of many immune cells, including macrophages and fibroblast-like cells called fibrocytes. The plasma protein serum amyloid P component (SAP; also known as pentraxin-2, PTX2) inhibits fibrocyte differentiation in vitro, and injections of SAP inhibit fibrosis in vivo. SAP also promotes the formation of immuno-regulatory Mreg macrophages. To elucidate the endogenous function of SAP, we used bleomycin aspiration to induce pulmonary inflammation and fibrosis in mice lacking SAP. Compared to wildtype C57BL/6 mice, we find that in Apcs^-/- “SAP knock-out” mice, bleomycin induces a more persistent inflammatory response and increased fibrosis. In both C57BL/6 and Apcs^-/- mice, injections of exogenous SAP reduce the accumulation of inflammatory macrophages and prevent fibrosis. The types of inflammatory cells present in the lungs following bleomycin-aspiration appear similar between C57BL/6 and Apcs^-/- mice, suggesting that the initial immune response is normal in the Apcs^-/- mice, and that a key endogenous function of SAP is to promote the resolution of inflammation and fibrosis.

FcγRI mediates serum amyloid P inhibition of fibrocyte differentiation

Fibrotic diseases, such as cardiac and pulmonary fibrosis, have a poor prognosis with no FDA approved therapies. Monocyte-derived, fibroblast-like cells, called fibrocytes, participate in the formation of fibrotic lesions. The conserved pentraxin protein SAP inhibits fibrocyte differentiation in cell culture, and injections of SAP significantly reduce fibrosis in several animal models. SAP binds to the receptors for the Fc portion of IgG (FcγR) and has been crystallized bound to FcγRIIa (CD32a). The in vivo activity of SAP appears to be dependent on the FcRγ. We find that mutagenesis of the residues critical for SAP binding to FcγRIIa only moderately decreases the ability of SAP to inhibit fibrocyte differentiation. In murine cells, deletion of FcRγ or FcγRI (CD64) significantly reduced sensitivity to SAP. Deletion of the combination of FcγRIIb, FcγRIIIa, and FcγRIV did not significantly affect sensitivity to SAP, whereas deletion of just the inhibitory receptor FcγRIIb (CD32b) increased sensitivity to SAP. In human cells, siRNA-mediated reduction of FcRγ or FcγRI levels significantly decreased sensitivity to SAP, whereas reduction of FcγRIIb levels increased sensitivity to SAP. These observations suggest that SAP, at least in part, uses FcγRI and FcRγ to inhibit fibrocyte differentiation.

Monocyte development inhibitor PRM-151 decreases corneal myofibroblast generation in rabbits

This study investigated whether PRM-151 (Promedior, Inc., Malvern, PA), a recombinant form of human pentraxin-2 (PTX-2, also referred to as serum amyloid P, hSAP), that inhibits differentiation of circulating monocytes into fibrocytes and profibrotic macrophages, could modulate generation of myofibroblasts after opacity-producing corneal injury in rabbits, and, therefore, have potential to reduce or prevent haze after PRK. Nine diopter PRK for myopia was performed with the VISX S4 IR laser. Four groups of 6 animals were treated in masked fashion: Group 1: 30 μl of topical PRM-151 (20 mg/ml) 6 times a day for 5 days; Group 2: 30 μl topical vehicle 6 times a day for 5 days; Group 3: 200 μl sub-conjunctival PRM-151 (total injection of 4 mg) immediately after surgery and every other day until day 8; Group 4: 200 μl sub-conjunctival injections of vehicle according to the same schedule as group 3. At one month after PRK, the animals were euthanized and immunohistochemistry was performed for the myofibroblast marker α-smooth muscle actin (SMA). The density of SMA+ cells/400× field in the central stroma was determined in each cornea. Myofibroblast density at one month after surgery was significantly lower (p = 0.006) after sub-conjunctival PRM-151 treatment (5.8 ± 2.8 cells/400× stromal field) compared to sub-conjunctival vehicle treatment (15.3 ± 2.9 cells/400× stromal field). There was no significant (p = 0.27) decrease in stromal myofibroblasts triggered by topical PRM-151 treatment (11.8 ± 6.6 cells/400× stromal field) compared to the topical vehicle treatment (14.2.8 ± 6.2 cells/400× stromal field). PRM-151 inhibits myofibroblast generation when administered by sub-conjunctival injection, but not when administered topically, after opacity-producing corneal injury. This study provides additional confirmation that bone marrow-derived cells contribute to corneal myofibroblast generation.

Serum amyloid P component facilitates DNA clearance and inhibits plasmid transfection: implications for human DNA vaccine

The demonstration that naked plasmid DNA can induce strong immune responses in mice has attracted considerable attention in the vaccine community. However, similar immunizations have been less/not effective in clinical trials during the past decade, and the underlying mechanisms remain unknown. In this study, we hypothesized that some DNA-binding proteins in human serum may serve as host barriers, responsible for the low efficiency of plasmids' transfection in vivo. Using proteomics, we showed that human serum amyloid P component (hSAP) is specifically present in human DNA-protein complexes. Further analysis indicated that hSAP effectively binds plasmid DNA, inhibits DNA transfection into somatic cells and facilitates the endocytosis of DNA by macrophages, whereas mouse SAP (mSAP) has similar, but much weaker, activities. In the presence of hSAP, the plasmid DNA expression in vivo and plasmid DNA-induced immune responses also significantly decreased. Therefore, our results suggest that hSAP contributes to extracellular DNA clearance and the inhibition of plasmid DNA transfection in vivo. This mechanism may be partly responsible for the insufficient immune responses to DNA vaccination in human beings; therefore, it may serve as a novel target for the improvement of DNA vaccines and DNA-based gene therapy.

Positive correlation between CD137 expression and complex stenosis morphology in patients with acute coronary syndromes

BACKGROUND

CD137, a member of the tumor necrosis factor receptor superfamily, has been reported to be expressed highly in patients with acute coronary syndromes. However, limited information is available on the relationship between CD137 expression and complex stenosis morphology in patients with acute coronary syndromes.

METHODS

Our study included normal controls (n=50), patients with stable angina (SA) (n=80) and patients with acute coronary syndromes (ACS), including unstable angina (UA) (n=70) and acute myocardial infarction (AMI) (n=100). The expression of CD137 in peripheral monocytes was analyzed by flow cytometry. Serum soluble CD137 (sCD137), MMP-9 and MMP-3 levels were measured by enzyme-linked immunosorbent assay kit. All coronary stenoses with ≥50% diameter reduction were assessed by angiographic coronary stenosis morphology.

RESULTS

Patients with ACS(n=170) showed a significant increase of CD137 [23.6±5.7 mean fluorescence intensity (MFI)] expression in peripheral monocytes compared with control (8.4±2.6 MFI) and SA group (7.9±2.1 MFI) (p<0.001). sCD137 also showed higher level in patients with ACS(30.2±8.7 ng/ml) than in control (6.2±1.8 ng/ml) and SA group (7.1±2.1 ng/ml) (p<0.001). Serum MMP-3 and MMP-9 in patients with ACS were 2-times greater than those in control and SA group. A positive correlation was found between MMP-9, MMP-3 and CD137 expression in peripheral monocytes as well as sCD137 levels. An obvious correlation was also observed between soluble or membrane-bound CD137 expression and complex coronary stenoses (r1=0.5548, r2=0.4652, and p<0.001). In the logistic regression model, the independent predictors of ACS were sCD137 (odds ratio 2.671, 95% CI 1.718-4.153, P=0.000), MMP-9 (1.431, 1.043-1.964, P=0.026) and MMP-3 (1.368, 1.038-1.817, P=0.018).

CONCLUSION

Patients with ACS showed significantly positive correlation between CD137 expression and complex coronary stenosis morphology. We speculate that the increased CD137 expression might represent or reflect an instability of atherosclerotic plaques in patients with ACS.

Human serum amyloid P functions as a negative regulator of the innate and adaptive immune responses to DNA vaccines

The utility of DNA vaccines has been limited by their failure to elicit sufficiently potent immune responses in many human applications, whereas DNA vaccinations in mice have been very successful. However, the underlying mechanisms remain unknown. We hypothesize that serum amyloid P component (SAP), which has a species-specific, DNA-binding ability, contributes to the differences between human and mice and then limits DNA vaccine's efficacy in vivo. In our study, DNA vaccine-induced adaptive immune responses were also significantly decreased in the human SAP (hSAP) transgenic mice. Using human promonocytic cell line THP-1-derived macrophages as a cell model, we found that cells incubated with a hSAP-DNA complex showed significant defects in innate immune activations, whereas mouse SAP had similar, albeit very weak, activities. hSAP also significantly inhibited the functions of two identified DNA sentinels, high-mobility group B protein 1 and antimicrobial peptide LL37, and redirected DNA update to FcRs leading to endocytosis and endosomal degradation. We also found that a chemical SAP inhibitor strongly recovered the suppressed innate immune responses to DNA in the presence of human serum and enhanced the immunogenicity of DNA vaccines in vivo. Our data indicated that SAP is a key negative regulator for innate immune responses to DNA and may be partly responsible for the insufficient immune responses after DNA vaccinations in humans. SAP suppression may be a novel strategy for improving efficacy of human DNA vaccines and requires further clinical investigations.

Positive correlation between pregnancy-associated plasma protein-A level and OX40 ligand expression in patients with acute coronary syndromes

OBJECTIVE

Increasing evidence show that serum pregnancy-associated plasma protein-A (PAPP-A) and OX40 ligand (OX40L) expression have been implicated in acute coronary syndromes (ACS). We investigated the relationship between PAPP-A level and OX40L in serum and membrane-bound OX40L in patients with ACS.

METHODS

The present study included normal controls (n=30), patients with stable angina (SA) (n=60) and patients with ACS, including unstable angina (UA) (n=50) and acute myocardial infarction (AMI) (n=30). Serum concentrations of PAPP-A and soluble OX40L (sOX40L) were determined with Elisa, whereas the expression of OX40L on monocytes were analyzed with flow cytometry.

RESULTS

The expression of OX40L in peripheral monocytes in patients with UA [25.6±5.5 mean fluorescence intensity (MFI)] and AMI (29.4±6.3MFI) were significantly higher than those in patients with SA (10.6±2.8MFI) and controls (11.1±3.5MFI). Both sOX40L and PAPP-A in patients with UA (15.7±4.9ng/mL, 25.4±6.8μg/mL, respectively) and AMI (17.1±5.3ng/mL, 26.3±5.6μg/mL, respectively) were significantly higher than those in patients with SA (3.4±1.4ng/mL, 9.6±2.1μg/mL, respectively) and controls (3.9±1.3ng/mL, 8.5±2.8μg/mL, respectively) (P<0.001). Interestingly, a positive correlation was found between sOX40L, membrane-bound OX40L and serum PAPP-A levels (r(1)=0.54, r(2)=0.51; P<0.0001). Both serum and membrane-bound OX40L and PAPP-A levels significantly correlated with complex coronary stenosis (r(1)=0.56, r(2)=0.55, r(3)=0.40; P<0.001).

CONCLUSION

PAPP-A level was significantly related to soluble and membrane-bound OX40L in patients with ACS. Enhanced level of serum PAPP-A and sOX40L might represent a prognostic marker for coronary disease activity.