Generation of human antibodies targeting human platelet antigen (HPA)-1a

Background: Fetal and neonatal alloimmune thrombocytopenia (FNAIT) is a condition during pregnancy, which can lead to thrombocytopenia and a bleeding tendency with intracranial hemorrhage (ICH) being the most concerning complication in the fetus or neonate. An incompatibility between human platelet antigen (HPA)-1a accounts for the majority of FNAIT cases. Binding of HPA-1a-specific alloantibodies to their target on fetal platelets and endothelial cells can induce apoptosis of megakaryocytes, disrupt platelet function, and impair angiogenesis. Currently, there is no screening program to identify pregnancies at risk for severe disease. A better understanding of HPA-1a-specific antibody heterogeneity in FNAIT could aid in identifying pathogenic antibody properties linked to severe disease. Study Design and Methods: This study aimed to isolate HPA-1a-specific B-cells from an HPA-1a-alloimmunized pregnant woman. Using fluorescently labeled HPA-1a-positive platelets, single B-cells were sorted and cultured for 10 days to stimulate antibody production. Subsequently, supernatants were tested for the presence of antibodies by enzyme-linked immunosorbent assay and their reactivity towards HPA-1a-positive platelets. Amplification and sequencing of variable regions allowed the generation of monoclonal antibodies using a HEK-Freestyle-based expression system. Results: Three platelet-specific B-cells were obtained and cloned of which two were specific for HPA-1a, named D- and M-204, while the third was specific for HLA class I, which was named L-204. Discussion: This study outlined an effective method for the isolation of HPA-1a-specific B-cells and the generation of monoclonal antibodies. Further characterization of these antibodies holds promise for better understanding the pathogenic nature of alloantibodies in FNAIT

Autoantibodies to Ezrin are an early sign of pancreatic cancer in humans and in genetically engineered mouse models

BACKGROUND: Pancreatic Ductal Adenocarcinoma (PDAC) is a highly aggressive malignancy with only a 5% 5-year survival rate. Reliable biomarkers for early detection are still lacking. The goals of this study were (a) to identify early humoral responses in genetically engineered mice (GEM) spontaneously developing PDAC; and (b) to test their diagnostic/predictive value in newly diagnosed PDAC patients and in prediagnostic sera. METHODS AND RESULTS: The serum reactivity of GEM from inception to invasive cancer, and in resectable or advanced human PDAC was tested by two-dimensional electrophoresis Western blot against proteins from murine and human PDAC cell lines, respectively. A common mouse-to-human autoantibody signature, directed against six antigens identified by MALDI-TOF mass spectrometry, was determined. Of the six antigens, Ezrin displayed the highest frequency of autoantibodies in GEM with early disease and in PDAC patients with resectable disease. The diagnostic value of Ezrin-autoantibodies to discriminate PDAC from controls was further shown by ELISA and ROC analyses (P < 0.0001). This observation was confirmed in prediagnostic sera from the EPIC prospective study in patients who eventually developed PDAC (with a mean time lag of 61.2 months between blood drawing and PDAC diagnosis). A combination of Ezrin-autoantibodies with CA19.9 serum levels and phosphorylated α-Enolase autoantibodies showed an overall diagnostic accuracy of 0.96 ± 0.02. CONCLUSIONS: Autoantibodies against Ezrin are induced early in PDAC and their combination with other serological markers may provide a predictive and diagnostic signature

Immunoassay for quantification of antigen-specific IgG fucosylation

BACKGROUND: Immunoglobulin G (IgG) antibodies serve a crucial immuno-protective function mediated by IgG Fc receptors (FcγR). Absence of fucose on the highly conserved N-linked glycan in the IgG Fc domain strongly enhances IgG binding and activation of myeloid and natural killer (NK) cell FcγRs. Although afucosylated IgG can provide increased protection (malaria and HIV), it also boosts immunopathologies in alloimmune diseases, COVID-19 and dengue fever. Quantifying IgG fucosylation currently requires sophisticated methods such as liquid chromatography-mass spectrometry (LC-MS) and extensive analytical skills reserved to highly specialized laboratories. METHODS: Here, we introduce the Fucose-sensitive Enzyme-linked immunosorbent assay (ELISA) for Antigen-Specific IgG (FEASI), an immunoassay capable of simultaneously quantitating and qualitatively determining IgG responses. FEASI is a two-tier immunoassay; the first assay is used to quantify antigen-specific IgG (IgG ELISA), while the second gives FcγRIIIa binding-dependent readout which is highly sensitive to both the IgG quantity and the IgG Fc fucosylation (FcγR-IgG ELISA). FINDINGS: IgG Fc fucosylation levels, independently determined by LC-MS and FEASI, in COVID-19 responses to the spike (S) antigen, correlated very strongly by simple linear regression (R2=0.93, p < 0.0001). The FEASI method was then used to quantify IgG levels and fucosylation in COVID-19 convalescent plasma which was independently validated by LC-MS. INTERPRETATION: FEASI can be reliably implemented to measure relative and absolute IgG Fc fucosylation and quantify binding of antigen-specific IgG to FcγR in a high-throughput manner accessible to all diagnostic and research laboratories. FUNDING: This work was funded by the Stichting Sanquin Bloedvoorziening (PPOC 19-08 and SQI00041) and ZonMW 10430 01 201 0021

Identification of Novel Tumor-Associated Antigens in Chronic Lymphocytic Leukemia (CLL) by Serological Proteome Analysis (SERPA)

Introduction: In this study, a serological proteome analysis (SERPA) was applied for the first time to identify novel tumor-associated antigens (Ags) capable of eliciting humoral immune responses in patients with chronic lymphocytic leukemia (CLL). SERPA has been demonstrated to be a valuable method to identify tumor associated Ags in several human solid and hematological malignancies. The identification and characterization of circulating antibodies (Abs) and corresponding Ags in CLL can provide useful information to understand cell transformation, predict clinical outcome, and develop immune-based interventions. Methods: SERPA was performed in 21 untreated patients. Proteins extracted from purified CLL cells were separated by 2-D electrophoresis (2-DE) to obtain proteomic maps which were blotted with corresponding sera by Western Blot to reveal Ab-based reactivity with autologous proteins. To verify the CLL specificity of Abs recognition, 7 out of 21 maps were also probed with sera collected from 7 healthy donors (HD). For identification, Ag spots in WB were aligned with proteins in 2-DE maps. The protein spots corresponding to the assigned Ags were excised from the gel, trypsin digested and analyzed by peptide mass fingerprint by MALDITOF Mass Spectrometry (MS) with the software MASCOT. T cells from 6 CLL patients and 3 HD were stimulated with autologous ENOA-pulsed and control dendritic cells (DC) and evaluated by IFN{gamma} ELISPOT assay. Ags surface expression was analyzed by flow cytometry. Statistical correlations were performed using t-test, Mann-Withney rank sum test and {chi}2-test. Results: Sixteen out of 21 CLL sera (76%) were immunoreactive and produced a total number of 45 Ag spots, whereas HD sera produced only 3 spots (p<.03). Eleven out of 16 (69%) reactive CLL sera recognized from 2 to 6 different Ags in each individual patients. MS analyses led to the identification of 16 different Ags and many of them were recognized by sera from different patients. Forty-eight percent of CLL sera reacted against α-Enolase (ENOA), whereas none of HD sera was ENOA reactive. The IGHV mutational status was available in 19 CLL patients: 10 were mutated (M), while 9 were unmutated (UM). Interestingly, ENOA was recognized by sera from 7/10 M patients (70%), but only by sera from 3/9 UM patients (33%). Cytofluoroimetric analyses performed in 7 patients showed that ENOA was undetectable on viable CLL cells surface, whereas it was translocated on the membrane of apoptotic CLL cells. Statistical correlation analyses showed that immunoreactive CLL patients are characterized by an early stage of disease. Moreover, ENOA-reactive patients have a better preserved immune system because they have higher numbers of CD3+ (p=.02), CD3+/CD4+ (p=.03) and CD3+/CD8+ (p=.05) cells in the peripheral blood than ENOA-unreactive patients. We also investigated the possibility to induce ENOA-specific T-cell immune responses in 6 CLL patients. ENOA-pulsed DC induced IFN{gamma} production in 4/6 patients (66%). The response was ENOA and CLL specific because: 1) it was not induced by unpulsed DC or DC pulsed with an irrelevant protein; 2) it was not induced when T cells from 3 HD were stimulated with autologous ENOA-pulsed DC. Interestingly, ENOA Abs were detectable by SERPA in 3 out of 4 (75%) patients with ENOA-induced T-cell responses, whereas they were undetectable in patients with unresponsive T cells. Correlations with the IGHV mutational status showed that all patients with ENOA-reactive T cells were M. Conclusions: These results indicate that ENOA is able to elicit specific humoral and cellular immune responses suggesting that this protein can be a promising biomarker and a potential target for immunotherapy in CLL

Divergent SARS-CoV-2-specific T and B cell responses in severe but not mild COVID-19 patients

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the causative agent of the current coronavirus disease 2019 (COVID-19) pandemic. Understanding the immune response that provides specific immunity but may also lead to immunopathology is crucial for the design of potential preventive and therapeutic strategies. Here, we characterized and quantified SARS-CoV-2 specific immune responses in patients with different clinical courses. Compared to individuals with a mild clinical presentation, CD4+ T cell responses were qualitatively impaired in critically ill patients. Strikingly, however, in these patients the specific IgG antibody response was remarkably strong. Furthermore, in these critically ill patients, a massive influx of circulating T cells into the lungs was observed, overwhelming the local T cell compartment, and indicative of vascular leakage. The observed disparate T and B cell responses could be indicative of a deregulated immune response in critically ill COVID-19 patients. This article is protected by copyright. All rights reserved

Divergent SARS-CoV-2-specific T- and B-cell responses in severe but not mild COVID-19 patients

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the causative agent of the current coronavirus disease 2019 (COVID-19) pandemic. Understanding the immune response that provides specific immunity but may also lead to immunopathology is crucial for the design of potential preventive and therapeutic strategies. Here, we characterized and quantified SARS-CoV-2-specific immune responses in patients with different clinical courses. Compared to individuals with a mild clinical presentation, CD4+ T-cell responses were qualitatively impaired in critically ill patients. Strikingly, however, in these patients the specific IgG antibody response was remarkably strong. Furthermore, in these critically ill patients, a massive influx of circulating T cells into the lungs was observed, overwhelming the local T-cell compartment, and indicative of vascular leakage. The observed disparate T- and B-cell responses could be indicative of a deregulated immune response in critically ill COVID-19 patients

Saliva SARS-CoV-2 antibody prevalence in children

COVID-19 patients produce circulating and mucosal antibodies. In adults, specific saliva antibodies have been detected. Nonetheless, seroprevalence is routinely investigated, while little attention has been paid to mucosal antibodies. We therefore assessed SARS-CoV-2-specific antibody prevalence in serum and saliva in children in the Netherlands. We assessed SARS-CoV-2 antibody prevalence in serum and saliva of 517 children attending medical services in the Netherlands (irrespective of COVID-19 exposure) from April to October 2020. The prevalence of SARS-CoV-2 spike (S), receptor binding domain (RBD), and nucleocapsid (N)-specific IgG and IgA were evaluated with an exploratory Luminex assay in serum and saliva and with the Wantai SARS-CoV-2 RBD total antibody enzyme-linked immunosorbent assay in serum. Using the Wantai assay, the RBD-specific antibody prevalence in serum was 3.3% (95% confidence interval [CI]. 1.9 to 5.3%). With the Luminex assay, we detected heterogeneity between antibodies for S, RBD, and N antigens, as IgG and IgA prevalence ranged between 3.6 and 4.6% in serum and between 0 and 4.4% in saliva. The Luminex assay also revealed differences between serum and saliva, with SARS-CoV-2-specific IgG present in saliva but not in serum for 1.5 to 2.7% of all children. Using multiple antigen assays, the IgG prevalence for at least two out of three antigens (S, RBD, or N) in serum or saliva can be calculated as 3.8% (95% CI, 2.3 to 5.6%). Our study displays the heterogeneity of the SARS-CoV-2 antibody response in children and emphasizes the additional value of saliva antibody detection and the combined use of different antigens. IMPORTANCE Comprehending humoral immunity to SARS-CoV-2, including in children, is crucial for future public health and vaccine strategies. Others have suggested that mucosal antibody measurement could be an important and more convenient tool to evaluate humoral immunity compared to circulating antibodies. Nonetheless, seroprevalence is routinely investigated, while little attention has been paid to mucosal antibodies. We show the heterogeneity of SARS-CoV-2 antibodies, in terms of both antigen specificity and differences between circulating and mucosal antibodies, emphasizing the additional value of saliva antibody detection next to detection of antibodies in serum