Vaccine-induced immune thrombotic thrombocytopenia is mediated by a stereotyped clonotypic antibody

Incidence and management of the main serious adverse events reported after COVID-19 vaccination

Coronavirus disease 2019 (COVID-19) caused by the severe acute respiratory syndrome coronavirus 2n first appeared in Wuhan, China in 2019. Soon after, it was declared a pandemic by the World Health Organization. The health crisis imposed by a new virus and its rapid spread worldwide prompted the fast development of vaccines. For the first time in human history, two vaccines based on recombinant genetic material technology were approved for human use. These mRNA vaccines were applied in massive immunization programs around the world, followed by other vaccines based on more traditional approaches. Even though all vaccines were tested in clinical trials prior to their general administration, serious adverse events, usually of very low incidence, were mostly identified after application of millions of doses. Establishing a direct correlation (the cause-effect paradigm) between vaccination and the appearance of adverse effects has proven challenging. This review focuses on the main adverse effects observed after vaccination, including anaphylaxis, myocarditis, vaccine-induced thrombotic thrombocytopenia, Guillain-Barré syndrome, and transverse myelitis reported in the context of COVID-19 vaccination. We highlight the symptoms, laboratory tests required for an adequate diagnosis, and briefly outline the recommended treatments for these adverse effects. The aim of this work is to increase awareness among healthcare personnel about the serious adverse events that may arise post-vaccination. Regardless of the ongoing discussion about the safety of COVID-19 vaccination, these adverse effects must be identified promptly and treated effectively to reduce the risk of complications.

Cerebral venous sinus thrombosis and thrombocytopenia due to heparin-independent anti-PF4 antibodies after adenovirus infection

Not available.

Structural Characterization of a Pathogenic Antibody Underlying Vaccine-Induced Immune Thrombotic Thrombocytopenia (VITT)

Vaccine-induced immune thrombotic thrombocytopenia (VITT) is a rare but dangerous side effect of adenoviral-vectored COVID-19 vaccines. VITT had been linked to production of autoantibodies recognizing platelet factor 4 (PF4). Here, we characterize anti-PF4 antibodies obtained from a VITT patient's blood. Intact mass measurements indicate that a significant fraction of these antibodies represent a limited number of clones. MS analysis of large antibody fragments (the light chain and the Fc/2 and Fd fragments of the heavy chain) confirms the monoclonal nature of this component of the anti-PF4 antibodies repertoire and reveals the presence of a mature complex biantennary N-glycan within the Fd segment. Peptide mapping using two complementary proteases and LC-MS/MS was used to determine the amino acid sequence of the entire light chain and over 98% of the heavy chain (excluding a short N-terminal segment). The sequence analysis allows the monoclonal antibody to be assigned to the IgG2 subclass and verifies that the light chain belongs to the λ-type. Incorporation of enzymatic de-N-glycosylation into the peptide mapping routine allows the N-glycan in the Fab region of the antibody to be localized to the framework 3 region of the VH domain. This novel N-glycosylation site is the result of a single mutation within the germline sequence. Peptide mapping also provides information on lower-abundance (polyclonal) components of the anti-PF4 antibody ensemble, revealing the presence of all four subclasses (IgG1-IgG4) and both types of the light chain (λ and κ). This case study demonstrates the power of combining the intact, middle-down, and bottom-up MS approaches for meaningful characterization of ultralow quantities of pathogenic antibodies extracted directly from patients' blood.

Biophysical studies do not reveal direct interactions between human PF4 and Ad26.COV2.S vaccine

BACKGROUND

COVID-19 vaccines have been widely used to control the SARS-CoV-2 pandemic. In individuals receiving replication-incompetent, adenovirus vector-based COVID-19 vaccines (eg, ChAdOx1 nCoV-19 [AstraZeneca] or Ad26.COV2.S [Johnson & Johnson/Janssen] vaccines), a very rare but serious adverse reaction has been reported and described as vaccine-induced immune thrombotic thrombocytopenia (VITT). The exact mechanism of VITT following Ad26.COV2.S vaccination is under investigation. Antibodies directed against human platelet factor 4 (PF4) are considered critical in the pathogenesis of VITT, suggesting similarities with heparin-induced thrombocytopenia. It has been postulated that components of these vaccines mimic the role of heparin by binding to PF4, triggering production of these anti-PF4 antibodies.

OBJECTIVES

This study aimed to investigate the potential interaction between human PF4 and Ad26.COV2.S vaccine using several biophysical techniques.

METHODS

Direct interaction of PF4 with Ad26.COV2.S vaccine was investigated using dynamic light scattering, biolayer interferometry, and surface plasmon resonance. For both biosensing methods, the Ad26.COV2.S vaccine was immobilized to the sensor surface and PF4 was used as analyte.

RESULTS

No direct interactions between PF4 and Ad26.COV2.S vaccine could be detected using dynamic light scattering and biolayer interferometry. Surface plasmon resonance technology was shown to be unsuitable to investigate these types of interactions.

CONCLUSION

Our findings make it very unlikely that direct binding of PF4 to Ad26.COV2.S vaccine or components thereof is driving the onset of VITT, although the occurrence of such interactions after immunization (potentially facilitated by unknown plasma or cellular factors) cannot be excluded. Further research is warranted to improve the understanding of the full mechanism of this adverse reaction.

Vaccine-Induced Immune Thrombotic Thrombocytopenia: Clinicopathologic Features and New Perspectives on Anti-PF4 Antibody-Mediated Disorders

INTRODUCTION

Vaccine-induced immune thrombotic thrombocytopenia (VITT) is a rare yet severe adverse complication first identified during the global vaccination effort against SARS-CoV-2 infection, predominantly observed following administration of the ChAdOx1-S (Oxford-AstraZeneca) and Ad26.CoV2.S (Johnson & Johnson/Janssen) adenoviral vector-based vaccines. Unlike other anti-platelet factor 4 (PF4) antibody-mediated disorders, such as heparin-induced thrombocytopenia (HIT), VITT arises with the development of platelet-activating anti-PF4 antibodies 4-42 days post-vaccination, typically featuring thrombocytopenia and thrombosis at unusual sites.

AIM

To explore the unique properties, pathogenic mechanisms, and long-term persistence of VITT antibodies in patients, in comparison with other anti-PF4 antibody-mediated disorders.

DISCUSSION

This review highlights the complexity of VITT as it differs in antibody behavior and clinical presentation from other anti-PF4-mediated disorders, including the high incidence rate of cerebral venous sinus thrombosis (CVST) and the persistence of anti-PF4 antibodies, necessitating a re-evaluation of long-term patient care strategies. The nature of VITT antibodies and the underlying mechanisms triggering their production remain largely unknown.

CONCLUSION

The rise in awareness and subsequent prompt recognition of VITT is paramount in reducing mortality. As vaccination campaigns continue, understanding the role of adenoviral vector-based vaccines in VITT antibody production is crucial, not only for its immediate clinical implications, but also for developing safer vaccines in the future.

Anti-PF4 immunothrombosis without proximate heparin or adenovirus vector vaccine exposure

ABSTRACT

Platelet-activating anti-platelet factor 4 (PF4)/heparin antibodies and anti-PF4 antibodies cause heparin-induced thrombocytopenia (HIT) and vaccine-induced immune thrombocytopenia and thrombosis (VITT), respectively. Diagnostic and treatment considerations differ somewhat between HIT and VITT. We identified patients with thrombocytopenia and thrombosis without proximate heparin exposure or adenovirus-based vaccination who tested strongly positive by PF4/polyanion enzyme-immunoassays and negative/weakly positive by heparin-induced platelet activation (HIPA) test but strongly positive by PF4-induced platelet activation (PIPA) test (ie, VITT-like profile). We tested these patients by a standard chemiluminescence assay that detects anti-PF4/heparin antibodies found in HIT (HemosIL AcuStar HIT-IgG(PF4-H)) as well as a novel chemiluminescence assay for anti-PF4 antibodies found in VITT. Representative control sera included an exploratory anti-PF4 antibody-positive but HIPA-negative/weak cohort obtained before 2020 (n = 188). We identified 9 patients with a clinical-pathological profile of a VITT-like disorder in the absence of proximate heparin or vaccination, with a high frequency of stroke (arterial, n = 3; cerebral venous sinus thrombosis, n = 4), thrombocytopenia (median platelet count nadir, 49 × 109/L), and hypercoagulability (greatly elevated D-dimer levels). VITT-like serological features included strong reactivity by PIPA (aggregation <10 minutes in 9/9 sera) and positive testing in the novel anti-PF4 chemiluminescence assay (3/9 also tested positive in the anti-PF4/heparin chemiluminescence assay). Our exploratory cohort identified 13 additional patient sera obtained before 2020 with VITT-like anti-PF4 antibodies. Platelet-activating VITT-like anti-PF4 antibodies should be considered in patients with thrombocytopenia, thrombosis, and very high D-dimer levels, even without a proximate exposure to heparin or adenovirus vector vaccines.

Thrombotic anti-PF4 immune disorders: HIT, VITT, and beyond

Antibodies against the chemokine platelet factor 4 (PF4) occur often, but only those that activate platelets induce severe prothrombotic disorders with associated thrombocytopenia. Heparin-induced thrombocytopenia (HIT) is the prototypic anti-PF4 disorder, mediated by strong activation of platelets through their FcγIIa (immunoglobulin G [IgG]) receptors (FcγRIIa). Concomitant pancellular activation (monocytes, neutrophils, endothelium) triggers thromboinflammation with a high risk for venous and arterial thrombosis. The classic concept of HIT is that anti-PF4/heparin IgG, recognizing antigen sites on (cationic) PF4 that form in the presence of (anionic) heparin, constitute the heparin-dependent antibodies that cause HIT. Accordingly, HIT is managed by anticoagulation with a nonheparin anticoagulant. In 2021, adenovirus vector COVID-19 vaccines triggered the rare adverse effect "vaccine-induced immune thrombotic thrombocytopenia" (VITT), also caused by anti-PF4 IgG. VITT is a predominantly heparin-independent platelet-activating disorder that requires both therapeutic-dose anticoagulation and inhibition of FcγRIIa-mediated platelet activation by high-dose intravenous immunoglobulin (IVIG). HIT and VITT antibodies bind to different epitopes on PF4; new immunoassays can differentiate between these distinct HIT-like and VITT-like antibodies. These studies indicate that (1) severe, atypical presentations of HIT ("autoimmune HIT") are associated with both HIT-like (heparin-dependent) and VITT-like (heparin-independent) anti-PF4 antibodies; (2) in some patients with severe acute (and sometimes chronic, recurrent) thrombosis, VITT-like antibodies can be identified independent of proximate heparin exposure or vaccination. We propose to classify anti-PF4 antibodies as type 1 (nonpathogenic, non- platelet activating), type 2 (heparin dependent, platelet activating), and type 3 (heparin independent, platelet activating). A key concept is that type 3 antibodies (autoimmune HIT, VITT) require anticoagulation plus an adjunct treatment, namely high-dose IVIG, to deescalate the severe anti-PF4 IgG-mediated hypercoagulability state.

Intravenous Administration of Ad26.COV2.S Does Not Induce Thrombocytopenia or Thrombotic Events or Affect SARS-CoV-2 Spike Protein Bioavailability in Blood Compared with Intramuscular Vaccination in Rabbits

Vaccine-induced immune thrombotic thrombocytopenia (VITT) is a very rare but serious adverse reaction that can occur after Ad26.COV2.S vaccination in humans, leading to thrombosis at unusual anatomic sites. One hypothesis is that accidental intravenous (IV) administration of Ad26.COV2.S or drainage of the vaccine from the muscle into the circulatory system may result in interaction of the vaccine with blood factors associated with platelet activation, leading to VITT. Here, we demonstrate that, similar to intramuscular (IM) administration of Ad26.COV2.S in rabbits, IV dosing was well tolerated, with no significant differences between dosing routes for the assessed hematologic, coagulation time, innate immune, or clinical chemistry parameters and no histopathologic indication of thrombotic events. For both routes, all other non-adverse findings observed were consistent with a normal vaccine response and comparable to those observed for unrelated or other Ad26-based control vaccines. However, Ad26.COV2.S induced significantly higher levels of C-reactive protein on day 1 after IM vaccination compared with an Ad26-based control vaccine encoding a different transgene, suggesting an inflammatory effect of the vaccine-encoded spike protein. Although based on a limited number of animals, these data indicate that an accidental IV injection of Ad26.COV2.S may not represent an increased risk for VITT.

COVID-19 vaccine-induced immune thrombotic thrombocytopenia: pathophysiology and diagnosis

Coronavirus disease-19 (COVID-19) vaccine-induced immune thrombotic thrombocytopenia (VITT) is a rare but serious clinical condition with high mortality rate in apparently healthy individuals without noticeable risk factors. VITT typically arises due to the administration of vaccines that possess recombinant adenoviral vectors, including ChAdOx1 nCov-19 (AstraZeneca) and Ad26 COV2.S (Johnson & Johnson/Janssen). Thrombosis frequently occurs at atypical sites, such as the cerebral or splanchnic circulations, in this particular pathological state. Similar to heparin-induced thrombotic thrombocytopenia (HITT), it seems that the cause of VITT is the misdirection of anti-platelet factor 4 antibodies (anti-PF4 Abs), an ancient antimicrobial mechanism. Anti-PF4 Abs in patients with VITT activates the coagulation system, leading to thrombosis. This process occurs through the stimulation of platelets (Plts) and neutrophils and subsequently release of neutrophil extracellular traps (NETs). Due to the potentially fatal consequences of VITT, early diagnosis is mandatory. In addition to thrombocytopenia, thrombosis, and the presence of anti-PF4 Abs, the day of symptoms onset and the elevation of D-dimer are also required for definitive diagnosis of VITT. The absence of one or more criteria can result in the exclusion of definitive VITT and lead to the diagnosis of probable, possible, or unlikely VITT.

Immunogenicity in Mice Immunized with Recombinant Adenoviruses Expressing Varicella-Zoster Virus Envelope Glycoprotein E

Herpes zoster (HZ) is a disease caused by the reactivation of latent varicella-zoster virus (VZV). The subunit vaccine, Shingrix®, and live attenuated vaccine, Zostavax®, could be used as an HZ vaccine that prevents HZ from being developed due to the reactivation of latent VZV in the sensory ganglia due to aging, stress or immunosuppression. In this study, the recombinant adenoviruses rChAd63/gE expressing glycoprotein E (gE) of VZV based on chimpanzee adenovirus serotype 63 (ChAd63) were constructed and investigated for the immunogenicity of different immune pathways in C57BL/6 mice. The results showed similar CD4+ T and CD8+ T cell responses to Shingrix® were induced in mice vaccinated using rChAd63/gE via different immune pathways. This study elucidates that recombinant adenoviruses expressing VZV gE could be appropriate for further development as a new HZ vaccine candidate via different immune pathways.

Reverse Engineering of a Pathogenic Antibody Reveals the Molecular Mechanism of Vaccine-Induced Immune Thrombotic Thrombocytopenia

The massive COVID-19 vaccine roll-out campaign illuminated a range of rare side effects, the most dangerous of which─vaccine-induced immune thrombotic thrombocytopenia (VITT)─is caused by adenoviral (Ad)-vectored vaccines. VITT occurrence had been linked to the production of pathogenic antibodies that recognize an endogenous chemokine, platelet factor 4 (PF4). Mass spectrometry (MS)-based evaluation of the ensemble of anti-PF4 antibodies obtained from a VITT patient's blood indicates that the major component is a monoclonal antibody. Structural characterization of this antibody reveals several unusual characteristics, such as the presence of an N-glycan in the Fab segment and high density of acidic amino acid residues in the complementarity-determining regions. A recombinant version of this antibody (RVT1) was generated by transient expression in mammalian cells based on the newly determined sequence. It captures the key properties of VITT antibodies such as their ability to activate platelets in a PF4 concentration-dependent fashion. Homology modeling of the Fab segment reveals a well-defined polyanionic paratope, and the docking studies indicate that the polycationic segment of PF4 readily accommodates two Fab segments, cross-linking the antibodies to yield polymerized immune complexes. Their existence was verified with native MS by detecting assemblies as large as (RVT1)3(PF4)2, pointing out at FcγRIIa-mediated platelet activation as the molecular mechanism underlying VITT clinical manifestations. In addition to the high PF4 affinity, RVT1 readily binds other polycationic targets, indicating a polyreactive nature of this antibody. This surprising promiscuity not only sheds light on VITT etiology but also opens up a range of opportunities to manage this pathology.

Chemokines, molecular drivers of thromboinflammation and immunothrombosis

Blood clotting is a finely regulated process that is essential for hemostasis. However, when dysregulated or spontaneous, it promotes thrombotic disorders. The fact that these are triggered, accompanied and amplified by inflammation is reflected in the term thromboinflammation that includes chemokines. The role of chemokines in thrombosis is therefore illuminated from a cellular perspective, where endothelial cells, platelets, red blood cells, and leukocytes may be both the source and target of chemokines. Chemokine-dependent prothrombotic processes may thereby occur independently of chemokine receptors or be mediated by chemokine receptors, although the binding and activation of classical G protein-coupled receptors and their signaling pathways differ from those of atypical chemokine receptors, which do not function via cell activation and recruitment. Regardless of binding to their receptors, chemokines can induce thrombosis by forming platelet-activating immune complexes with heparin or other polyanions that are pathognomonic for HIT and VITT. In addition, chemokines can bind to NETs and alter their structure. They also change the electrical charge of the cell surface of platelets and interact with coagulation factors, thereby modulating the balance of fibrinolysis and coagulation. Moreover, CXCL12 activates CXCR4 on platelets independently of classical migratory chemokine activity and causes aggregation and thrombosis via the PI3Kβ and Btk signaling pathways. In contrast, typical chemokine-chemokine receptor interactions are involved in the processes that contribute to the adhesiveness of the endothelium in the initial phase of venous thrombosis, where neutrophils and monocytes subsequently accumulate in massive numbers. Later, the reorganization and resolution of a thrombus require coordinated cell migration and invasion of the thrombus, and, as such, indeed, chemokines recruit leukocytes to existing thrombi. Therefore, chemokines contribute in many independent ways to thrombosis.

Viral-vectored respiratory mucosal vaccine strategies

Increasing global concerns of pandemic respiratory viruses highlight the importance of developing optimal vaccination strategies that encompass vaccine platform, delivery route, and regimens. The decades-long effort to develop vaccines to combat respiratory infections such as influenza, respiratory syncytial virus, and tuberculosis has met with challenges, including the inability of systemically administered vaccines to induce respiratory mucosal (RM) immunity. In this regard, ample preclinical and available clinical studies have demonstrated the superiority of RM vaccination to induce RM immunity over parenteral route of vaccination. A great stride has been made in developing vaccines for RM delivery against respiratory pathogens, including M. tuberculosis and SARS-CoV-2. In particular, inhaled aerosol delivery of adenoviral-vectored vaccines has shown significant promise.

Vaccine-Induced Immune Thrombocytopenia and Thrombosis (VITT)-Insights from Clinical Cases, In Vitro Studies and Murine Models

An effective worldwide vaccination campaign started and is still being carried out in the face of the coronavirus disease 2019 (COVID-19) pandemic. While vaccines are great tools to confront the pandemic, predominantly adenoviral vector-based vaccines can cause a rare severe adverse effect, termed vaccine-induced immune thrombocytopenia and thrombosis (VITT), in about 1 in 100,000 vaccinated individuals. VITT is diagnosed 5-30 days post-vaccination and clinically characterized by thrombocytopenia, strongly elevated D-dimer levels, platelet-activating anti-platelet factor 4 (PF4) antibodies and thrombosis, especially at atypical sites such as the cerebral venous sinus and/or splanchnic veins. There are striking similarities between heparin-induced thrombocytopenia (HIT) and VITT. Both are caused by anti-PF4 antibodies, causing platelet and leukocyte activation which results in massive thrombo-inflammation. However, it is still to be determined why PF4 becomes immunogenic in VITT and which constituent of the vaccine triggers the immune response. As VITT-like syndromes are increasingly reported in patients shortly after viral infections, direct virus-PF4 interactions might be most relevant. Here we summarize the current information and hypotheses on the pathogenesis of VITT and address in vivo models, especially murine models for further studies on VITT.

Long-term outcome in vaccine-induced immune thrombocytopenia and thrombosis

BACKGROUND

Rapid diagnosis and treatment has improved outcome of patients with vaccine-induced immune thrombocytopenia and thrombosis (VITT). However, after the acute episode, many questions on long-term management of VITT remained unanswered.

OBJECTIVES

To analyze, in patients with VITT, the long-term course of anti-platelet factor 4 (PF4) antibodies; clinical outcomes, including risk of recurrent thrombosis and/or thrombocytopenia; and the effects of new vaccinations.

METHODS

71 patients with serologically confirmed VITT in Germany were enrolled into a prospective longitudinal study and followed for a mean of 79 weeks from March 2021 to January 2023. The course of anti-PF4 antibodies was analyzed by consecutive anti-PF4/heparin immunoglobulin G enzyme-linked immunosorbent assay and PF4-enhanced platelet activation assay.

RESULTS

Platelet-activating anti-PF4 antibodies became undetectable in 62 of 71 patients (87.3%; 95% CI, 77.6%-93.2%). In 6 patients (8.5%), platelet-activating anti-PF4 antibodies persisted for >18 months. Five of 71 patients (7.0%) showed recurrent episodes of thrombocytopenia and/or thrombosis; in 4 of them (80.0%), alternative explanations beside VITT were present. After further COVID-19 vaccination with a messenger RNA vaccine, no reactivation of platelet-activating anti-PF4 antibodies or new thrombosis was observed. No adverse events occurred in our patients subsequently vaccinated against influenza, tick-borne encephalitis, varicella, tetanus, diphtheria, pertussis, and polio. No new thrombosis occurred in the 24 patients (33.8%) who developed symptomatic SARS-CoV-2 infection following recovery from acute VITT.

CONCLUSION

Once the acute episode of VITT has passed, patients appear to be at low risk for recurrent thrombosis and/or thrombocytopenia.

Thrombosis with thrombocytopenia syndrome: A database review of clinical trial and post-marketing experience with Ad26.COV2.S

BACKGROUND

Thrombosis with thrombocytopenia syndrome (TTS) is a very rare disorder described after vaccination with adenoviral vector-based COVID-19 vaccines. Co-occurring thrombosis with thrombocytopenia reported after vaccination can be a proxy for identification of TTS.

METHODS

Descriptive database review of all cases of co-occurring (within 42 days) thrombosis with thrombocytopenia in participants in Ad26.COV2.S clinical trials or recipients of Ad26.COV2.S in real-world clinical practice. Cases were retrieved from Janssens' clinical trial and Global Medical Safety databases.

RESULTS

There were 34 cases of co-occurring thrombosis with thrombocytopenia in Ad26.COV2.S recipients (46 per 100,000 person-years) and 15 after placebo (75 per 100,000 person-years) in clinical trials. Among Ad26.COV2.S recipients, mean age at the time of the event was 63 years (range 25-85), 82 % were male, mean time-to-onset 112 days (range 8-339) post-last Ad26.COV2.S dose, 26 events occurred post-dose-1, and 7 within a 28-day risk window post-vaccination. Diagnostic certainty was evaluated using Brighton Collaboration, US Centers for Disease Control and Prevention, and European Medicines Agency Pharmacovigilance Risk Assessment Committee case definitions. One case met the highest level of diagnostic certainty for all 3 definitions. There were 355 spontaneous reports of co-occurring thrombosis with thrombocytopenia in the Global Medical Safety database, 47 % males, 85 % within 28-days after vaccination. Twenty-seven cases met the highest level of diagnostic certainty for all definitions, 21 female, 19 with cerebral venous sinus thrombosis, age-range 18-68 years. Time-to-onset was 7-14 days post-vaccination in 20 cases. There were 8 fatalities.

CONCLUSION

TTS induced by Ad26.COV2.S is very rare. Most co-occurring thrombosis with thrombocytopenia does not constitute TTS.

Immunoglobulin repertoire restriction characterizes the serological responses of patients with predominantly antibody deficiency

BACKGROUND

Predominantly antibody deficiency (PAD) is the most common category of inborn errors of immunity and is underpinned by impaired generation of appropriate antibody diversity and quantity. In the clinic, responses are interrogated by assessment of vaccination responses, which is central to many PAD diagnoses. However, the composition of the generated antibody repertoire is concealed from traditional quantitative measures of serological responses. Leveraging modern mass spectrometry-based proteomics (MS-proteomics), it is possible to elaborate the molecular features of specific antibody repertoires, which may address current limitations of diagnostic vaccinology.

OBJECTIVES

We sought to evaluate serum antibody responses in patients with PAD following vaccination with a neo-antigen (severe acute respiratory syndrome coronavirus-2 vaccination) using MS-proteomics.

METHODS

Following severe acute respiratory syndrome coronavirus-2 vaccination, serological responses in individuals with PAD and healthy controls (HCs) were assessed by anti-S1 subunit ELISA and neutralization assays. Purified anti-S1 subunit IgG and IgM was profiled by MS-proteomics for IGHV subfamily usage and somatic hypermutation analysis.

RESULTS

Twelve patients with PAD who were vaccine-responsive were recruited with 11 matched vaccinated HCs. Neutralization and end point anti-S1 titers were lower in PAD. All subjects with PAD demonstrated restricted anti-S1 IgG antibody repertoires, with usage of <5 IGHV subfamilies (median: 3; range 2-4), compared to ≥5 for the 11 HC subjects (P < .001). IGHV3-7 utilization was far less common in patients with PAD than in HCs (2 of 12 vs 10 of 11; P = .001). Amino acid substitutions due to somatic hypermutation per subfamily did not differ between groups. Anti-S1 IgM was present in 64% and 50% of HC and PAD cohorts, respectively, and did not differ significantly between HCs and patients with PAD.

CONCLUSIONS

This study demonstrates the breadth of anti-S1 antibodies elicited by vaccination at the proteome level and identifies stereotypical restriction of IGHV utilization in the IgG repertoire in patients with PAD compared with HC subjects. Despite uniformly pauci-clonal antibody repertoires some patients with PAD generated potent serological responses, highlighting a possible limitation of traditional serological techniques. These findings suggest that IgG repertoire restriction is a key feature of antibody repertoires in PAD.

Structural characterization of a pathogenic antibody underlying vaccine-induced immune thrombotic thrombocytopenia (VITT)

Vaccine-induced immune thrombotic thrombocytopenia (VITT) is a rare but extremely dangerous side effect that has been reported for several adenoviral (Ad)-vectored COVID-19 vaccines. VITT pathology had been linked to production of antibodies that recognize platelet factor 4 (PF4), an endogenous chemokine. In this work we characterize anti-PF4 antibodies obtained from a VITT patient's blood. Intact-mass MS measurements indicate that a significant fraction of this ensemble is comprised of antibodies representing a limited number of clones. MS analysis of large antibody fragments (the light chain, as well as the Fc/2 and Fd fragments of the heavy chain) confirms the monoclonal nature of this component of the anti-PF4 antibodies repertoire, and reveals the presence of a fully mature complex biantennary N-glycan within its Fd segment. Peptide mapping using two complementary proteases and LC-MS/MS analysis were used to determine the amino acid sequence of the entire light chain and over 98% of the heavy chain (excluding a short N-terminal segment). The sequence analysis allows the monoclonal antibody to be assigned to IgG2 subclass and verify that the light chain belongs to the λ-type. Incorporation of enzymatic de- N -glycosylation into the peptide mapping routine allows the N -glycan in the Fab region of the antibody to be localized to the framework 3 region of the V H domain. This novel N -glycosylation site (absent in the germline sequence) is a result of a single mutation giving rise to an NDT motif in the antibody sequence. Peptide mapping also provides a wealth of information on lower-abundance proteolytic fragments derived from the polyclonal component of the anti-PF4 antibody ensemble, revealing the presence of all four subclasses (IgG1 through IgG4) and both types of the light chain (λ and κ). The structural information reported in this work will be indispensable for understanding the molecular mechanism of VITT pathogenesis.

Vaccine-induced immune thrombotic thrombocytopenia: what do we know hitherto?

Vaccine-induced immune thrombotic thrombocytopenia (VITT), also known as thrombosis with thrombocytopenia syndrome, is a catastrophic and life-threatening reaction to coronavirus disease 2019 (COVID-19) vaccines, which occurs disproportionately in response to vaccination with non-replicating adenovirus vector (AV) vaccines. The mechanism of VITT is not well defined and it has not been resolved why cases of VITT are predominated by vaccination with AV vaccines. However, virtually all VITT patients have positive platelet-activating anti-platelet factor 4 (PF4) antibody titers. Subsequently, platelets are activated and depleted in an Fcγ-receptor IIa (FcγRIIa or CD32a)-dependent manner, but it is not clear why or how the anti-PF4 response is mounted. This review describes the pathogenesis of VITT and provides insight into possible mechanisms that prompt the formation of a PF4/polyanion complex, which drives VITT pathology, as an amalgam of current experimental data or hypotheses.

Adenoviral-vectored next-generation respiratory mucosal vaccines against COVID-19

The world is in need of next-generation COVID-19 vaccines. Although first-generation injectable COVID-19 vaccines continue to be critical tools in controlling the current global health crisis, continuous emergence of SARS-CoV-2 variants of concern has eroded the efficacy of these vaccines, leading to staggering breakthrough infections and posing threats to poor vaccine responders. This is partly because the humoral and T-cell responses generated following intramuscular injection of spike-centric monovalent vaccines are mostly confined to the periphery, failing to either access or be maintained at the portal of infection, the respiratory mucosa (RM). In contrast, respiratory mucosal-delivered vaccine can induce immunity encompassing humoral, cellular, and trained innate immunity positioned at the respiratory mucosa that may act quickly to prevent the establishment of an infection. Viral vectors, especially adenoviruses, represent the most promising platform for RM delivery that can be designed to express both structural and nonstructural antigens of SARS-CoV-2. Boosting RM immunity via the respiratory route using multivalent adenoviral-vectored vaccines would be a viable next-generation vaccine strategy.

Isolated anti-Ro52 identifies a severe subset of Sjögren’s syndrome patients

Introduction

Serum autoantibodies targeting the SSA/Ro proteins are a key component of the classification criteria for the diagnosis of Sjögren’s syndrome (SS). Most patients' serum reacts with both Ro60 and Ro52 proteins. Here we compare the molecular and clinical characteristics of patients diagnosed with SS with anti-Ro52 in the presence or absence of anti-Ro60/La autoantibodies.

Methods

A cross-sectional study was performed. Patients in the SS biobank at Westmead Hospital (Sydney, Australia) that were positive for anti-Ro52 were included and stratified based on the absence (isolated) or presence (combined) of anti-Ro60/La, measured by line immunoassay. We examined clinical associations and the serological and molecular characteristics of anti-Ro52 using ELISA and mass spectrometry in serological groups.

Results

A total of 123 SS patients were included for study. SS patients with isolated anti-Ro52 (12%) identified a severe serological subset characterised by higher disease activity, vasculitis, pulmonary involvement, rheumatoid factor (RhF) and cryoglobulinaemia. Serum antibodies reacting with Ro52 in the isolated anti-Ro52 subset displayed less isotype switching, less immunoglobulin variable region subfamily usage and a lower degree of somatic hypermutation than the combined anti-Ro52 subset.

Conclusions

In our cohort of SS patients, isolated anti-Ro52 represents a severe subset of SS, and is associated with the presence of cryoglobulinaemia. We therefore provide clinical relevance to the stratification of SS patients by their sero-reactivities. It is possible that the autoantibody patterns may be immunological epiphenomena of the underlying disease process, and further work is required to unearth the mechanisms of the differential clinical phenotypes.

Platelet-activating functional assay resolution in vaccine-induced immune thrombotic thrombocytopenia: differential alignment to PF4 ELISA platforms

Background

Anti-platelet factor 4 (PF4) antibodies in vaccine-induced immune thrombotic thrombocytopenia (VITT) appear to be transient, with discrepant persistence depending on the platform used for detection.

Objectives

We aimed to report a longitudinal study of antibody persistence using 2 ELISA platforms and 2 platelet-activating functional assays in a clinical cohort of patients with VITT referred for follow-up testing.

Methods

In total, 32 Australian patients with VITT or pre-VITT, confirmed by expert adjudication, with samples referred for clinical follow-up were included. Clinical follow-up assays, including Stago and Hyphen ELISAs, procoagulant platelet flow cytometry, and modified PF4-serotonin-release assay, were performed according to the pattern of reactivity for that patient at diagnosis.

Results

The median follow-up was 24 weeks after diagnosis. A general decline in anti-PF4 antibody levels and platelet-activating capacity over time was observed with a more rapid median time to resolution of 16 weeks by functional assay vs 24 weeks by Stago ELISA. Decline in platelet-activating antibody levels detected by functional assays mirrored Stago ELISA titer but not Hyphen. However, 87% of patients received a documented second vaccination and 74% received an mRNA booster with no reported adverse events.

Conclusion

Anti-PF4 antibodies persist longer than functional platelet-activating antibodies in VITT but do not warrant avoidance of subsequent vaccinations. Persistence detection is assay-dependent. Stago ELISA may be a surrogate where functional assays are unavailable for follow-up testing of confirmed patients with VITT.

Mechanisms of Thrombosis in Heparin-Induced Thrombocytopenia and Vaccine-Induced Immune Thrombotic Thrombocytopenia

Heparin-induced thrombocytopenia (HIT) and vaccine-induced immune thrombotic thrombocytopenia (VITT) are rare, iatrogenic immune-mediated conditions with high rates of thrombosis-related morbidity and mortality. HIT is a long-recognized reaction to the administration of the common parenterally administered anticoagulant heparin (or its derivatives), while VITT is a new, distinct syndrome occurring in response to adenovirus-based vaccines against coronavirus disease 2019 and potentially other types of vaccines. A feature of both HIT and VITT is paradoxical thrombosis despite a characteristic low platelet count, mediated by the presence of platelet-activating antibodies to platelet factor 4. Several additional factors have also been suggested to contribute to clot formation in HIT and/or VITT, including monocytes, tissue factor, microparticles, endothelium, the formation of neutrophil extracellular traps, complement, procoagulant platelets, and vaccine components. In this review, we discuss the literature to date regarding mechanisms contributing to thrombosis in both HIT and VITT and explore the pathophysiological similarities and differences between the two conditions.

Vaccine-induced immune thrombotic thrombocytopenia

Vaccine-induced immune thrombotic thrombocytopenia (VITT) is primarily a complication of adenoviral vector-based covid-19 vaccination. In VITT, thrombocytopenia and thrombosis mediated by anti-platelet factor 4 (PF4) antibodies can be severe, often characterized by thrombosis at unusual sites such as the cerebral venous sinus and splanchnic circulation. Like in heparin-induced thrombocytopenia (HIT) and spontaneous HIT, VITT antibodies recognize PF4-polyanion complexes and activate PF4-treated platelets but additionally bind to un-complexed PF4, a critical finding that could be leveraged for more specific detection of VITT. Intravenous immunoglobulin and non-heparin-based anticoagulation remain the mainstay of treatment. Second dose/boosters of mRNA covid-19 vaccines appear safe in patients with adenoviral vector-associated VITT. Emerging data is consistent with the possibility that ultra-rare cases of VITT may be seen in the setting of mRNA and virus-like particle (VLP) technology-based vaccinations and until more data is available, it is prudent to consider VITT in the differential diagnosis of all post-vaccine thrombosis and thrombocytopenia reactions.

Public Health Management of the COVID-19 Pandemic in Australia: The Role of the Morrison Government

The Australian Commonwealth government has four health-related responsibilities during the SARS-CoV-2 pandemic: to provide national leadership; to manage external borders; to protect residents of residential aged care facilities; and to approve, procure and roll-out tests and vaccines. State governments are responsible for determining what public health measures are appropriate and implementing them-including managing the border quarantine arrangements and the testing, tracing, and isolation regime-and managing the hospital response. This paper analyses the national government's response to the pandemic and discusses why it has attracted a thesaurus of negative adjectives.