Broadly neutralizing antibodies overcome SARS-CoV-2 Omicron antigenic shift.

The recently emerged SARS-CoV-2 Omicron variant encodes 37 amino acid substitutions in the spike protein, 15 of which are in the receptor-binding domain (RBD), thereby raising concerns about the effectiveness of available vaccines and antibody-based therapeutics. Here we show that the Omicron RBD binds to human ACE2 with enhanced affinity, relative to the Wuhan-Hu-1 RBD, and binds to mouse ACE2. Marked reductions in neutralizing activity were observed against Omicron compared to the ancestral pseudovirus in plasma from convalescent individuals and from individuals who had been vaccinated against SARS-CoV-2, but this loss was less pronounced after a third dose of vaccine. Most monoclonal antibodies that are directed against the receptor-binding motif lost in vitro neutralizing activity against Omicron, with only 3 out of 29 monoclonal antibodies retaining unaltered potency, including the ACE2-mimicking S2K146 antibody1. Furthermore, a fraction of broadly neutralizing sarbecovirus monoclonal antibodies neutralized Omicron through recognition of antigenic sites outside the receptor-binding motif, including sotrovimab2, S2X2593 and S2H974. The magnitude of Omicron-mediated immune evasion marks a major antigenic shift in SARS-CoV-2. Broadly neutralizing monoclonal antibodies that recognize RBD epitopes that are conserved among SARS-CoV-2 variants and other sarbecoviruses may prove key to controlling the ongoing pandemic and future zoonotic spillovers.

Tracking the immune response profiles elicited by the BNT162b2 vaccine in COVID-19 unexperienced and experienced individuals.

Multiple vaccines have been approved to control COVID-19 pandemic, with Pfizer/BioNTech (BNT162b2) being widely used. We conducted a longitudinal analysis of the immune response elicited after three doses of the BNT162b2 vaccine in individuals who have previously experienced SARS-CoV-2 infection and in unexperienced ones. We conducted immunological analyses and single-cell transcriptomics of circulating T and B lymphocytes, combined to CITE-seq or LIBRA-seq, and VDJ-seq. We found that antibody levels against SARS-CoV-2 Spike, NTD and RBD from wild-type, delta and omicron VoCs show comparable dynamics in both vaccination groups, with a peak after the second dose, a decline after six months and a restoration after the booster dose. The antibody neutralization activity was maintained, with lower titers against the omicron variant. Spike-specific memory B cell response was sustained over the vaccination schedule. Clonal analysis revealed that Spike-specific B cells were polyclonal, with a partial clone conservation from natural infection to vaccination. Spike-specific T cell responses were oriented towards effector and effector memory phenotypes, with similar trends in unexperienced and experienced individuals. The CD8 T cell compartment showed a higher clonal expansion and persistence than CD4 T cells. The first two vaccinations doses tended to induce new clones rather than promoting expansion of pre-existing clones. However, we identified a fraction of Spike-specific CD8 T cell clones persisting from natural infection that were boosted by vaccination and clones specifically induced by vaccination. Collectively, our observations revealed a moderate effect of the second dose in enhancing the immune responses elicited after the first vaccination. Differently, we found that a third dose was necessary to restore comparable levels of neutralizing antibodies and Spike-specific T and B cell responses in individuals who experienced a natural SARS-CoV-2 infection.

Identification of two autoantigens recognised by circulating autoantibodies as potential biomarkers for diagnosing giant cell arteritis.

OBJECTIVES: Giant cell arteritis (GCA) is a common vasculitis affecting patients aged 50 and older. GCA leads to chronic inflammation of large/medium-sized vessel walls with complications such as permanent vision loss and risk of stroke and aortic aneurysms. Early diagnosis is crucial and relies on temporal artery biopsy (TAB) and ultrasound imaging of temporal and axillary arteries. However, these methods have limitations. Serum biomarkers as autoantibodies have been reported but with inconclusive data for their use in the clinical setting. Additionally, C-reactive protein and erythrocyte sedimentation rate are non-specific and limited in reflecting disease activity, particularly in patients treated with IL-6 inhibitors. This study aimed to identify serum autoantibodies as new diagnostic biomarkers for GCA using a human protein array. METHODS: One commercial and one proprietary human protein array were used for antibody profiling of sera from patients with GCA (n=55), Takayasu (TAK n=7), and Healthy Controls (HC n=28). The identified candidate autoantigens were purified and tested for specific autoantibodies by ELISA. RESULTS: Antibodies against two proteins, VSIG10L (V-Set and Immunoglobulin Domain Containing 10 Like) and DCBLD1 (discoidin), were identified and found to be associated with GCA, with an overall prevalence of 43-57%, respectively, and high specificity as individual antibodies. A control series of TAK sera tested negative. CONCLUSIONS: Detecting GCA-specific autoantibodies may offer a new, non-invasive tool for improving our diagnostic power in GCA. Even though cell-mediated immune responses are crucial for GCA pathogenesis, this finding opens the way for investigating the additional role of humoral immune responses in the disease.

SARS-COV-2 specific t-cells in patients with thyroid disorders related to COVID-19 are enriched in the thyroid and acquire a tissue-resident memory phenotype.

BACKGROUND: SARS-CoV-2 infections have been associated with the onset of thyroid disorders like classic subacute thyroiditis (SAT) or atypical SAT upon severe COVID disease (COV-A-SAT). Little is known about thyroid anti-viral immune responses. OBJECTIVES: To define the role of T-cells in COV-A-SAT. METHODS: T-cells from COV-A-SAT patients were analyzed by multi-dimensional flow cytometry, UMAP and DiffusionMap dimensionality reduction and FlowSOM clustering. T-cells from COVID-naïve healthy donors, patients with autoimmune thyroiditis (ATD) and with SAT following COVID vaccination were analyzed as controls. T-cells were analyzed four and eight months post-infection in peripheral blood and in thyroid specimen obtained by ultrasound-guided fine needle aspiration. SARS-COV2-specific T-cells were identified by cytokine production induced by SARS-COV2-derived peptides and with COVID peptide-loaded HLA multimers after HLA haplotyping. RESULTS: COV-A-SAT was associated with HLA-DRB1*13 and HLA-B*57. COV-A-SAT patients contained activated Th1- and cytotoxic CD4+ and CD8+ effector cells four months post-infection, which acquired a quiescent memory phenotype after eight months. Anti-SARS-CoV-2-specific T-cell responses were readily detectable in peripheral blood four months post-infection, but were reduced after eight months. CD4+ and CD8+ tissue-resident memory cells (TRM) were present in the thyroid, and circulating CXCR3+T-cells identified as their putative precursors. SARS-CoV-2-specific T-cells were enriched in the thyroid, and acquired a TRM phenotype eight months post-infection. CONCLUSIONS: The association of COV-A-SAT with specific HLA haplotypes suggests a genetic predisposition and a key role for T-cells. COV-A-SAT is characterized by a prolonged systemic anti-viral effector T-cell response and the late generation of COVID-specific TRM in the thyroid target tissue.

Plasma Proteomic Variables Related to COVID-19 Severity: An Untargeted nLC-MS/MS Investigation.

Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) infection leads to a wide range of clinical manifestations and determines the need for personalized and precision medicine. To better understand the biological determinants of this heterogeneity, we explored the plasma proteome of 43 COVID-19 patients with different outcomes by an untargeted liquid chromatography-mass spectrometry approach. The comparison between asymptomatic or pauci-symptomatic subjects (MILDs), and hospitalised patients in need of oxygen support therapy (SEVEREs) highlighted 29 proteins emerged as differentially expressed: 12 overexpressed in MILDs and 17 in SEVEREs. Moreover, a supervised analysis based on a decision-tree recognised three proteins (Fetuin-A, Ig lambda-2chain-C-region, Vitronectin) that are able to robustly discriminate between the two classes independently from the infection stage. In silico functional annotation of the 29 deregulated proteins pinpointed several functions possibly related to the severity; no pathway was associated exclusively to MILDs, while several only to SEVEREs, and some associated to both MILDs and SEVEREs; SARS-CoV-2 signalling pathway was significantly enriched by proteins up-expressed in SEVEREs (SAA1/2, CRP, HP, LRG1) and in MILDs (GSN, HRG). In conclusion, our analysis could provide key information for 'proteomically' defining possible upstream mechanisms and mediators triggering or limiting the domino effect of the immune-related response and characterizing severe exacerbations.

Novel biomarkers for primary biliary cholangitis to improve diagnosis and understand underlying regulatory mechanisms.

BACKGROUND AND AIMS: Primary biliary cholangitis is an autoimmune biliary disease characterized by injury of bile ducts, eventually leading to cirrhosis and death. In most cases, anti-mitochondrial antibodies and persistently elevated serum alkaline phosphatase are the basis for the serological diagnosis. Anti-nuclear antibodies are also useful and may indicate a more aggressive diseases course. In patients in which anti-mitochondrial antibodies are not detected, an accurate diagnosis requires liver histology. This study aims at identifying specific biomarkers for the serological diagnosis of primary biliary cholangitis. METHODS: Sera from patients affected by primary biliary cholangitis, primary sclerosing cholangitis, hepatitis C virus (with and without cryoglobulinemia), hepatocarcinoma and healthy donors were tested on a protein array representing 1658 human proteins. The most reactive autoantigens were confirmed by DELFIA analysis on expanded cohorts of the same mentioned serum classes, and on autoimmune hepatitis sera, using anti-PDC-E2 as reference biomarker. RESULTS: Two autoantigens, SPATA31A3 and GARP, showed high reactivity with primary biliary cholangitis sera, containing or not anti-mitochondrial antibodies. Their combination with PDC-E2 allowed to discriminate primary biliary cholangitis from all tested control classes with high sensitivity and specificity. We found that GARP expression is upregulated upon exposure to biliary salts in human cholangiocytes, an event involving EGFR and insulin pathways. GARP expression was also detected in biliary duct cells of PBC patients. CONCLUSIONS: This study highlighted SPATA31A3 and GARP as new biomarkers for primary biliary cholangitis and unravelled molecular stimuli underlying GARP expression in human cholangiocytes.

FAT1: a potential target for monoclonal antibody therapy in colon cancer.

BACKGROUND: Colorectal cancer (CRC) is one of the major causes of cancer-associated mortality worldwide. The currently approved therapeutic agents have limited efficacy. METHODS: The atypical cadherin FAT1 was discovered as a novel CRC-associated protein by using a monoclonal antibody (mAb198.3). FAT1 expression was assessed in CRC cells by immunohistochemistry (IHC), immunoblots, flow cytometry and confocal microscopy. In addition, in vitro and in vivo tumour models were done to assess FAT1 potential value for therapeutic applications. RESULTS: The study shows that FAT1 is broadly expressed in primary and metastatic CRC stages and detected by mAb198.3, regardless of KRAS and BRAF mutations. FAT1 mainly accumulates at the plasma membrane of cancer cells, whereas it is only marginally detected in normal human samples. Moreover, the study shows that FAT1 has an important role in cell invasiveness while it does not significantly influence apoptosis. mAb198.3 specifically recognises FAT1 on the surface of colon cancer cells and is efficiently internalised. Furthermore, it reduces cancer growth in a colon cancer xenograft model. CONCLUSIONS: This study provides evidence that FAT1 and mAb198.3 may offer new therapeutic opportunities for CRC including the tumours resistant to current EGFR-targeted therapies.

Angiopoietin-like 7, a novel pro-angiogenetic factor over-expressed in cancer.

Angiopoietin-like (ANGPTL) proteins are secreted proteins showing structural similarity to members of the angiopoietin family. Some ANGPTL proteins possess pleiotropic activities, being involved in cancer lipid, glucose energy metabolisms, and angiogenesis. ANGPTL7 is the less characterized member of the family whose functional role is only marginally known. In this study, we provide experimental evidences that ANGPTL7 is over-expressed in different human cancers. To understand the role played by ANGPTL7 in tumor biology, we asked whether ANGPTL7 is endogenously expressed by malignant cells or in response to environmental stimuli. We found that ANGPTL7 is marginally expressed under standard growth condition while it is specifically up-regulated by hypoxia. Interestingly, the protein is secreted and partially associated with the exosomal fraction, suggesting that it could be found in the systemic circulation of oncologic patients and act in an endocrine way. Moreover, we found that ANGPTL7 exerts a pro-angiogenetic effect on human differentiated endothelial cells by stimulating their proliferation, motility, invasiveness, and capability to form capillary-like networks while it does not stimulate progenitor endothelial cells. Finally, we showed that ANGPTL7 promotes vascularization in vivo in the mouse Matrigel sponge assay, thereby accrediting this molecule as a pro-angiogenic factor.

Surface interactome in Streptococcus pyogenes.

Very few studies have so far been dedicated to the systematic analysis of protein interactions occurring between surface and/or secreted proteins in bacteria. Such interactions are expected to play pivotal biological roles that deserve investigation. Taking advantage of the availability of a detailed map of surface and secreted proteins in Streptococcus pyogenes (group A Streptococcus (GAS)), we used protein array technology to define the "surface interactome" in this important human pathogen. Eighty-three proteins were spotted on glass slides in high density format, and each of the spotted proteins was probed for its capacity to interact with any of the immobilized proteins. A total of 146 interactions were identified, 25 of which classified as "reciprocal," namely, interactions that occur irrespective of which of the two partners was immobilized on the chip or in solution. Several of these interactions were validated by surface plasmon resonance and supported by confocal microscopy analysis of whole bacterial cells. By this approach, a number of interesting interactions have been discovered, including those occurring between OppA, DppA, PrsA, and TlpA, proteins known to be involved in protein folding and transport. These proteins, all localizing at the septum, might be part, together with HtrA, of the recently described ExPortal complex of GAS. Furthermore, SpeI was found to strongly interact with the metal transporters AdcA and Lmb. Because SpeI strictly requires zinc to exert its function, this finding provides evidence on how this superantigen, a major player in GAS pathogenesis, can acquire the metal in the host environment, where it is largely sequestered by carrier proteins. We believe that the approach proposed herein can lead to a deeper knowledge of the mechanisms underlying bacterial invasion, colonization, and pathogenesis.

Multi high-throughput approach for highly selective identification of vaccine candidates: the Group A Streptococcus case.

We propose an experimental strategy for highly accurate selection of candidates for bacterial vaccines without using in vitro and/or in vivo protection assays. Starting from the observation that efficacious vaccines are constituted by conserved, surface-associated and/or secreted components, the strategy contemplates the parallel application of three high throughput technologies, i.e. mass spectrometry-based proteomics, protein array, and flow-cytometry analysis, to identify this category of proteins, and is based on the assumption that the antigens identified by all three technologies are the protective ones. When we tested this strategy for Group A Streptococcus, we selected a total of 40 proteins, of which only six identified by all three approaches. When the 40 proteins were tested in a mouse model, only six were found to be protective and five of these belonged to the group of antigens in common to the three technologies. Finally, a combination of three protective antigens conferred broad protection against a panel of four different Group A Streptococcus strains. This approach may find general application as an accelerated and highly accurate path to bacterial vaccine discovery.

Approach to discover T- and B-cell antigens of intracellular pathogens applied to the design of Chlamydia trachomatis vaccines.

Natural immunity against obligate and/or facultative intracellular pathogens is usually mediated by both humoral and cellular immunity. The identification of those antigens stimulating both arms of the immune system is instrumental for vaccine discovery. Although high-throughput technologies have been applied for the discovery of antibody-inducing antigens, few examples of their application for T-cell antigens have been reported. We describe how the compilation of the immunome, here defined as the pool of immunogenic antigens inducing T- and B-cell responses in vivo, can lead to vaccine candidates against Chlamydia trachomatis. We selected 120 C. trachomatis proteins and assessed their immunogenicity using two parallel high-throughput approaches. Protein arrays were generated and screened with sera from C. trachomatis-infected patients to identify antibody-inducing antigens. Splenocytes from C. trachomatis-infected mice were stimulated with 79 proteins, and the frequency of antigen-specific CD4(+)/IFN-γ(+) T cells was analyzed by flow cytometry. We identified 21 antibody-inducing antigens, 16 CD4(+)/IFN-γ(+)-inducing antigens, and five antigens eliciting both types of responses. Assessment of their protective activity in a mouse model of Chlamydia muridarum lung infection led to the identification of seven antigens conferring partial protection when administered with LTK63/CpG adjuvant. Protection was largely the result of cellular immunity as assessed by CD4(+) T-cell depletion. The seven antigens provided robust additive protection when combined in four-antigen combinations. This study paves the way for the development of an effective anti-Chlamydia vaccine and provides a general approach for the discovery of vaccines against other intracellular pathogens.

SARS-CoV-2: A Glance at the Innate Immune Response Elicited by Infection and Vaccination.

The COVID-19 pandemic caused by Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) has led to almost seven million deaths worldwide. SARS-CoV-2 causes infection through respiratory transmission and can occur either without any symptoms or with clinical manifestations which can be mild, severe or, in some cases, even fatal. Innate immunity provides the initial defense against the virus by sensing pathogen-associated molecular patterns and triggering signaling pathways that activate the antiviral and inflammatory responses, which limit viral replication and help the identification and removal of infected cells. However, temporally dysregulated and excessive activation of the innate immune response is deleterious for the host and associates with severe COVID-19. In addition to its defensive role, innate immunity is pivotal in priming the adaptive immune response and polarizing its effector function. This capacity is relevant in the context of both SARS-CoV-2 natural infection and COVID-19 vaccination. Here, we provide an overview of the current knowledge of the innate immune responses to SARS-CoV-2 infection and vaccination.

Protocol for the detection of defined T cell clones in a heterogeneous cell population.

Identifying defined T cell clones within a polyclonal population is key to clarifying their phenotype and function. Here, we present a protocol for detecting specified T cell clones in a heterogeneous cell population. We describe steps for stimulating human CD4+ T cells isolated from blood with a protein antigen, sorting antigen-specific cells by fluorescence-activated cell sorting, and detecting among these the presence of predefined T cell clones, based on their T cell receptor (TCR). TCR cDNA is amplified through 5'-RACE (TCR-SMART) and detected by qPCR. For complete details on the use and execution of this protocol, please refer to Notarbartolo et al. (2021).1.

Mapping of functional SARS-CoV-2 receptors in human lungs establishes differences in variant binding and SLC1A5 as a viral entry modulator of hACE2.

BACKGROUND: The COVID-19 pandemic is an infectious disease caused by SARS-CoV-2. The first step of SARS-CoV-2 infection is the recognition of angiotensin-converting enzyme 2 (ACE2) receptors by the receptor-binding domain (RBD) of the viral Spike (S) glycoprotein. Although the molecular and structural bases of the SARS-CoV-2-RBD/hACE2 interaction have been thoroughly investigated in vitro, the relationship between hACE2 expression and in vivo infection is less understood. METHODS: Here, we developed an efficient SARS-CoV-2-RBD binding assay suitable for super resolution microscopy and simultaneous hACE2 immunodetection and mapped the correlation between hACE2 receptor abundance and SARS-CoV-2-RBD binding, both in vitro and in human lung biopsies. Next, we explored the specific proteome of SARS-CoV-2-RBD/hACE2 through a comparative mass spectrometry approach. FINDINGS: We found that only a minority of hACE2 positive spots are actually SARS-CoV-2-RBD binding sites, and that the relationship between SARS-CoV-2-RBD binding and hACE2 presence is variable, suggesting the existence of additional factors. Indeed, we found several interactors that are involved in receptor localization and viral entry and characterized one of them: SLC1A5, an amino acid transporter. High-resolution receptor-binding studies showed that co-expression of membrane-bound SLC1A5 with hACE2 predicted SARS-CoV-2 binding and entry better than hACE2 expression alone. SLC1A5 depletion reduces SARS-CoV-2 binding and entry. Notably, the Omicron variant is more efficient in binding hACE2 sites, but equally sensitive to SLC1A5 downregulation. INTERPRETATION: We propose a method for mapping functional SARS-CoV-2 receptors in vivo. We confirm the existence of hACE2 co-factors that may contribute to differential sensitivity of cells to infection. FUNDING: This work was supported by an unrestricted grant from "Fondazione Romeo ed Enrica Invernizzi" to Stefano Biffo and by AIRC under MFAG 2021 - ID. 26178 project - P.I. Manfrini Nicola.

TMEM123 a key player in immune surveillance of colorectal cancer.

Colorectal cancer (CRC) is a leading cause of cancer-associated death. In the tumor site, the interplay between effector immune cells and cancer cells determines the balance between tumor elimination or outgrowth. We discovered that the protein TMEM123 is over-expressed in tumour-infiltrating CD4 and CD8 T lymphocytes and it contributes to their effector phenotype. The presence of infiltrating TMEM123+ CD8+ T cells is associated with better overall and metastasis-free survival. TMEM123 localizes in the protrusions of infiltrating T cells, it contributes to lymphocyte migration and cytoskeleton organization. TMEM123 silencing modulates the underlying signaling pathways dependent on the cytoskeletal regulator WASP and the Arp2/3 actin nucleation complex, which are required for synaptic force exertion. Using tumoroid-lymphocyte co-culture assays, we found that lymphocytes form clusters through TMEM123, anchoring to cancer cells and contributing to their killing. We propose an active role for TMEM123 in the anti-cancer activity of T cells within tumour microenvironment.

A 12-month follow-up of the immune response to SARS-CoV-2 primary vaccination: evidence from a real-world study.

A real-world population-based longitudinal study, aimed at determining the magnitude and duration of immunity induced by different types of vaccines against COVID-19, started in 2021 by enrolling a cohort of 2,497 individuals at time of their first vaccination. The study cohort included both healthy adults aged ≤65 years and elderly subjects aged >65 years with two or more co-morbidities. Here, patterns of anti-SARS-CoV-2 humoral and cell-mediated specific immune response, assessed on 1,182 remaining subjects, at 6 (T6) and 12 months (T12) after the first vaccine dose, are described. At T12 median anti-Spike IgG antibody levels were increased compared to T6. The determinants of increased anti-Spike IgG were the receipt of a third vaccine dose between T6 and T12 and being positive for anti-Nucleocapside IgG at T12, a marker of recent infection, while age had no significant effect. The capacity of T12 sera to neutralize in vitro the ancestral B strain and the Omicron BA.5 variant was assessed in a subgroup of vaccinated subjects. A correlation between anti-S IgG levels and sera neutralizing capacity was identified and higher neutralizing capacity was evident in healthy adults compared to frail elderly subjects and in those who were positive for anti-Nucleocapside IgG at T12. Remarkably, one third of T12 sera from anti-Nucleocapside IgG negative older individuals were unable to neutralize the BA.5 variant strain. Finally, the evaluation of T-cell mediated immunity showed that most analysed subjects, independently from age and comorbidity, displayed Spike-specific responses with a high degree of polyfunctionality, especially in the CD8 compartment. In conclusion, vaccinated subjects had high levels of circulating antibodies against SARS-CoV-2 Spike protein 12 months after the primary vaccination, which increased as compared to T6. The enhancing effect could be attributable to the administration of a third vaccine dose but also to the occurrence of breakthrough infection. Older individuals, especially those who were anti-Nucleocapside IgG negative, displayed an impaired capacity to neutralize the BA.5 variant strain. Spike specific T-cell responses, able to sustain immunity and maintain the ability to fight the infection, were present in most of older and younger subjects assayed at T12.

Corrigendum: TMEM123 a key player in immune surveillance of colorectal cancer.

[This corrects the article DOI: 10.3389/fimmu.2023.1194087.].

Synthetic carbohydrate-binding agents neutralize SARS-CoV-2 by inhibiting binding of the spike protein to ACE2.

Developing strategies against the SARS-CoV-2 is currently a main research subject. SARS-CoV-2 infects host cells by binding to human ACE2 receptors. Both, virus and ACE2, are highly glycosylated, and exploiting glycans of the SARS-CoV-2 envelope as binding sites for ACE2 represents a virus strategy for attacking the human host. We report here that a family of mannose-binding synthetic carbohydrate-binding agents (CBAs) inhibits SARS-CoV-2 infection, showing broad neutralizing activity vs. several variants of the spike protein. Preliminary tests indicated that the investigated CBAs interact with the spike protein rather than with ACE2. For a lead compound (IDS060), which has been selected among others for its lack of cytotoxicity, evidence of binding to the RBD of the spike protein has been found by NMR experiments, while competitive binding assays in the presence of IDS060 showed inhibition of binding of RBD to hACE2, although neutralizing activity was also observed with variants showing reduced or depleted binding.

Corrigendum: The Impact of Anti-rheumatic Drugs on the Seroprevalence of Anti-SARS-CoV-2 Antibodies in a Cohort of Patients With Inflammatory Arthritis: The MAINSTREAM Study.

[This corrects the article DOI: 10.3389/fmed.2022.850858.].

Production of anti-PF4 antibodies in antiphospholipid antibody-positive patients is not affected by COVID-19 vaccination.

BACKGROUND: Antibodies against cationic platelet chemokine, platelet factor 4 (PF4/CXCL4), have been described in heparin-induced thrombocytopenia (HIT), but also in patients positive for antiphospholipid antibodies (aPL) even in the absence of heparin treatment and HIT-related clinical manifestations. Anti-PF4 antibodies have been recently described also in subjects who developed thrombosis with thrombocytopenia syndrome (TTS) in association with adenoviral vector-based, but not with mRNA-based, COVID-19 vaccines. OBJECTIVE: To investigate whether COVID-19 vaccination affects the production of anti-PF4 antibodies in aPL-positive patients and in control groups. METHODS: Anti-PF4 immunoglobulins were detected in patients' and controls' serum samples by ELISA and their ability to activate normal platelets was assessed by the platelet aggregation test. RESULTS: Anti-PF4 were found in 9 of 126 aPL-positive patients, 4 of 50 patients with COVID-19, 9 of 49 with other infections, and 1 of 50 aPL-negative patients with systemic lupus erythematosus. Clinical manifestations of TTS were not observed in any aPL patient positive for anti-PF4, whose serum failed to cause platelet aggregation. The administration of COVID-19 vaccines did not affect the production of anti-PF4 immunoglobulins or their ability to cause platelet aggregation in 44 aPL-positive patients tested before and after vaccination. CONCLUSIONS: Heparin treatment-independent anti-PF4 antibodies can be found in aPL-positive patients and asymptomatic carriers, but their presence, titre as well as in vitro effect on platelet activation are not affected by COVID-19 vaccination.