Anti-PF4 levels of patients with VITT do not reduce 4 months following AZD1222 vaccination
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- Evaluated articles (Rapid Reviews Infectious Diseases)
Abstract
Background
Anti-Platelet Factor 4 (PF4) IgG antibodies that activate platelets via FcγRIIa have been shown to be an important part of the pathophysiology of vaccine-induced immune thrombocytopenia and thrombosis (VITT). There is now extensive literature on its presentation and initial management. There is no literature however on what happens to these patients following discharge.
Methods
We collected clinical data and samples from seven patients presenting with VITT and followed them up for 82-145 days. We also collected clinical samples from them at last follow-up. Testing for anti-PF4/heparin antibodies was done using an anti-PF4/heparin enzymatic immunoassay. Flow Cytometry was used to look at FcγRIIa levels on patient platelets. Light Transmission Aggregometry with patient serum and healthy donor / patient platelets was used to analyse platelet responsiveness, in the presence and absence of PF4.
Findings
All patients were discharged on direct oral anticoagulants. Two patients remain completely symptom free, three have ongoing headaches, two have residual neurological deficits. Two patients developed mild thrombocytopenia and worsening headache (but without cerebral venous sinus thrombosis) and were retreated, one of these with rituximab. All patients, except the one treated with rituximab, had similar anti-PF4 antibody titres at 80-120 days to their levels at diagnosis. Platelets from patients at follow-up had normal levels of FcγRIIa and had normal responses to thrombin and collagen-related-peptide. Patient serum from diagnosis strongly activated healthy donor platelets in the presence of PF4. Serum from follow-up was much weaker at stimulating platelets, even in the presence of PF4.
Interpretation
This study shows that despite similar PF4 antibody titres at diagnosis and during follow-up, there are further differences in patient serum, that are not apparent from currently used testing, that result in lower levels of platelet activation during the follow-up period. Further understanding of these factors are important in order to assess duration of anticoagulation for these patients.
Funding
This work was supported by an Accelerator Grant (AA/18/2/34218) from the British Heart Foundation (BHF) and by a National Institute for Health Research (NIHR) grant.
Key points
PF4 antibody titres do not reduce up to 4-months post ChAdOx1 nCoV-19 in patients with VITT
Despite similar PF4 antibody titres, diagnostic serum is more potent at activating platelets in the presence of PF4 than follow-up serum.
Article activity feed
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Pier Meroni, Maria Orietta Borghi
Review 3: "Anti-PF4 levels of patients with VITT do not reduce 4 months following AZD1222 vaccination"
This paper claims that, although anti-PF4 antibody levels remain high in VITT patients months after follow up, it is not associated with increased platelet activation Reviewers found it timely and reliable but in need of minor revisions on its methodology and discussion.
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Strength of evidence
Reviewers: Kochawan Boonyawat (Mahidol University) | 📗📗📗📗◻️
Helmuth Haslacher, Thomas Perkmann (Medical University of Vienna) | 📒📒📒◻️◻️
Pier Meroni, Maria Orietta Borghi (Fondazione Istituto Auxologico Italiano) |📗📗📗📗◻️ -
Helmuth Haslacher, Thomas Perkmann
Review 2: "Anti-PF4 levels of patients with VITT do not reduce 4 months following AZD1222 vaccination"
This paper claims that, although anti-PF4 antibody levels remain high in VITT patients months after follow-up, it is not associated with increased platelet activation Reviewers found it timely and reliable but in need of minor revisions on its methodology and discussion.
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Kochawan Boonyawat
Review 1: "Anti-PF4 levels of patients with VITT do not reduce 4 months following AZD1222 vaccination"
This paper claims that, although anti-PF4 antibody levels remain high in VITT patients months after follow-up, it is not associated with increased platelet activation Reviewers found it timely and reliable but in need of minor revisions on its methodology and discussion.
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SciScore for 10.1101/2021.08.17.21262138: (What is this?)
Please note, not all rigor criteria are appropriate for all manuscripts.
Table 1: Rigor
Ethics Consent: Informed consent was provided by the patients or by their next of kin in those who lacked capacity.
Field Sample Permit: Collection of blood from these patients (including those lacking capacity) was approved under research ethics granted to the University of Birmingham Human Biomaterial Resource Centre (North West – Haydock Research Ethics Committee, reference: 15/NW/0079, amendment 3, 19/11/2018).
IRB: Collection of blood from these patients (including those lacking capacity) was approved under research ethics granted to the University of Birmingham Human Biomaterial Resource Centre (North West – Haydock Research Ethics Committee, reference: 15/NW/0079, amendment 3, 19/11/2018).
IAC…SciScore for 10.1101/2021.08.17.21262138: (What is this?)
Please note, not all rigor criteria are appropriate for all manuscripts.
Table 1: Rigor
Ethics Consent: Informed consent was provided by the patients or by their next of kin in those who lacked capacity.
Field Sample Permit: Collection of blood from these patients (including those lacking capacity) was approved under research ethics granted to the University of Birmingham Human Biomaterial Resource Centre (North West – Haydock Research Ethics Committee, reference: 15/NW/0079, amendment 3, 19/11/2018).
IRB: Collection of blood from these patients (including those lacking capacity) was approved under research ethics granted to the University of Birmingham Human Biomaterial Resource Centre (North West – Haydock Research Ethics Committee, reference: 15/NW/0079, amendment 3, 19/11/2018).
IACUC: Ethical approval for collecting blood from healthy volunteers was granted by Birmingham University Internal Ethical Review Committee (reference: ERN_11-0175, assessed 22/3/2021).Sex as a biological variable not detected. Randomization not detected. Blinding not detected. Power Analysis not detected. Table 2: Resources
Antibodies Sentences Resources All studies were performed in line with the Declaration of Helsinki. Materials: PF4 was from Chromatec GmbH (Greifswald, Germany), collagen-related-peptide (CRP) was from CambCol Ltd (Ely, UK), FITC-conjugated mouse anti-human CD32a antibody was from BD Pharminogen (Wokingham, UK), FITC-conjugated IgG1 control mouse antibody was from Dako (Santa Clara, CA). CRPsuggested: NoneIgG1suggested: NonePF4 antibody testing: Testing for anti-PF4/heparin antibodies was done using an anti-PF4/heparin enzymatic immunoassay (EIA, LIFECODES PF4 enhanced assay; Immucor GTI Diagnostics) for IgG, IgM, and IgA PF4-heparin antibodies. anti-PF4/heparinsuggested: NoneIgA PF4-heparinsuggested: NoneWashed platelets (2×107) were stained for 30 min with mouse anti-human CD32a antibody or FITC control antibody. anti-human CD32asuggested: NoneResults from OddPub: We did not detect open data. We also did not detect open code. Researchers are encouraged to share open data when possible (see Nature blog).
Results from LimitationRecognizer: An explicit section about the limitations of the techniques employed in this study was not found. We encourage authors to address study limitations.Results from TrialIdentifier: No clinical trial numbers were referenced.
Results from Barzooka: We did not find any issues relating to the usage of bar graphs.
Results from JetFighter: We did not find any issues relating to colormaps.
Results from rtransparent:- Thank you for including a conflict of interest statement. Authors are encouraged to include this statement when submitting to a journal.
- Thank you for including a funding statement. Authors are encouraged to include this statement when submitting to a journal.
- No protocol registration statement was detected.
Results from scite Reference Check: We found no unreliable references.
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