Platelet-neutrophil interaction in COVID-19 and vaccine-induced thrombotic thrombocytopenia.

Coronavirus disease 2019 (COVID-19) is known to commonly induce a thrombotic diathesis, particularly in severely affected individuals. So far, this COVID-19-associated coagulopathy (CAC) has been partially explained by hyperactivated platelets as well as by the prothrombotic effects of neutrophil extracellular traps (NETs) released from neutrophils. However, precise insight into the bidirectional relationship between platelets and neutrophils in the pathophysiology of CAC still lags behind. Vaccine-induced thrombotic thrombocytopenia (VITT) is a rare autoimmune disorder caused by auto-antibody formation in response to immunization with adenoviral vector vaccines. VITT is associated with life-threatening thromboembolic events and thus, high fatality rates. Our concept of the thrombophilia observed in VITT is relatively new, hence a better understanding could help in the management of such patients with the potential to also prevent VITT. In this review we aim to summarize the current knowledge on platelet-neutrophil interplay in COVID-19 and VITT.

Whole Blood Procoagulant Platelet Flow Cytometry Protocol for Heparin-Induced Thrombocytopenia (HIT) and Vaccine-Induced Immune Thrombotic Thrombocytopenia (VITT) Testing.

Heparin-induced thrombocytopenia (HIT) is a well-characterized, iatrogenic complication of heparin anticoagulation with significant morbidity. In contrast, vaccine-induced immune thrombotic thrombocytopenia (VITT) is a recently recognized severe prothrombotic complication of adenoviral vaccines, including the ChAdOx1 nCoV-19 (Vaxzevria, AstraZeneca) and Ad26.COV2.S (Janssen, Johnson & Johnson) vaccines against COVID-19. The diagnosis of HIT and VITT involve laboratory testing for antiplatelet antibodies by immunoassays followed by confirmation by functional assays to detect platelet-activating antibodies. Functional assays are critical to detect pathological antibodies due to the varying sensitivity and specificity of immunoassays. This chapter presents a protocol for a novel whole blood flow cytometry-based assay to detect procoagulant platelets in healthy donor blood in response to plasma from patients suspected of HIT or VITT. A method to identify suitable healthy donors for HIT and VITT testing is also described.

Multiple Electrode Aggregometry (Multiplate): Functional Assay for Vaccine-Induced (Immune) Thrombotic Thrombocytopenia (VITT).

Vaccine-induced immune thrombotic thrombocytopenia (VITT) was first described in 2021 and represents an adverse reaction to adenoviral vector COVID-19 vaccines AstraZeneca ChAdOx1 nCoV-19 (AZD1222) and Johnson & Johnson Ad26.COV2.S vaccine. VITT is a severe immune platelet activation syndrome with an incidence of 1-2 per 100,000 vaccinations. The features of VITT include thrombocytopenia and thrombosis within 4-42 days of first dose of vaccine. Affected individuals develop platelet-activating antibodies against platelet factor 4 (PF4). The International Society on Thrombosis and Haemostasis recommends both an antigen-binding assay (enzyme-linked immunosorbent assay, ELISA) and a functional platelet activation assay for the diagnostic workup of VITT. Here, the application of multiple electrode aggregometry (Multiplate) is presented as a functional assay for VITT.

Serotonin Release Assay: Functional Assay for Heparin- and Vaccine-Induced (Immune) Thrombotic Thrombocytopenia.

The serotonin release assay (SRA) has been the gold-standard assay for detection of heparin-dependent platelet-activating antibodies and integral for the diagnosis for heparin-induced thrombotic thrombocytopenia (HIT). In 2021, a thrombotic thrombocytopenic syndrome was reported after adenoviral vector COVID-19 vaccination. This vaccine-induced thrombotic thrombocytopenic syndrome (VITT) proved to be a severe immune platelet activation syndrome manifested by unusual thrombosis, thrombocytopenia, very elevated plasma D-dimer, and a high mortality even with aggressive therapy (anticoagulation and plasma exchange). While the platelet-activating antibodies in both HIT and VITT are directed toward platelet factor 4 (PF4), important differences have been found. These differences have required modifications to the SRA to improve detection of functional VITT antibodies. Functional platelet activation assays remain essential in the diagnostic workup of HIT and VITT. Here we detail the application of SRA for the assessment of HIT and VITT antibodies.

Heparin-Induced Thrombotic Thrombocytopenia (HITT) and Vaccine-Induced Immune Thrombotic Thrombocytopenia (VITT): Similar but Different.

Heparin-induced thrombocytopenia (HIT) represents an autoimmune process whereby antibodies are formed against heparin in complex with platelet factor 4 (PF4) after heparin administration. These antibodies can be detected by a variety of immunological assays, including ELISA (enzyme-linked immunosorbent assay) and by chemiluminescence on the AcuStar instrument. However, pathological HIT antibodies are those that activate platelets in a platelet activation assay and cause thrombosis in vivo. We would tend to call this condition heparin-induced thrombotic thrombocytopenia (HITT), although some workers instead use the truncated abbreviation HIT. Vaccine-induced (immune) thrombotic thrombocytopenia (VITT) instead reflects an autoimmune process whereby antibodies are formed against PF4 after administration of a vaccine, most notably adenovirus-based vaccines directed against COVID-19 (coronavirus disease 2019). Although both VITT and HITT reflect similar pathological processes, they have different origins and are detected in different ways. Most notable is that anti-PF4 antibodies in VITT can only be detected immunologically by ELISA assays, tending to be negative in rapid assays such as that using the AcuStar. Moreover, functional platelet activation assays otherwise used for HITT may need to be modified to detect platelet activation in VITT.

Endovascular treatment for vaccine-induced cerebral venous sinus thrombosis and thrombocytopenia following ChAdOx1 nCoV-19 vaccination: a report of three cases.

BACKGROUND: Vaccine-induced thrombosis and thrombocytopenia (VITT) is a rare complication following ChAdOx1 nCoV-19 vaccination. Cerebral venous sinus thrombosis (CVST) is overrepresented in VITT and is often associated with multifocal venous thromboses, concomitant hemorrhage and poor outcomes. Hitherto, endovascular treatments have not been reviewed in VITT-related CVST. METHODS: Patient records from a tertiary neurosciences center were reviewed to identify patients who had endovascular treatment for CVST in VITT. RESULTS: Patient records from 1 January 2021 to 20 July 2021 identified three patients who underwent endovascular treatment for CVST in the context of VITT. All were female and the median age was 52 years. The location of the CVST was highly variable. Two-thirds of the patients had multifocal dural sinus thromboses (sigmoid, transverse, straight and superior sagittal) as well as internal jugular vein thromboses. Intracerebral hemorrhage occurred in all patients; subarachnoid blood was noted in two of them, and intraparenchymal hemorrhage occurred in all. There was one periprocedural parenchymal extravasation which abated on temporary cessation of anticoagulation. Outcome data revealed a 90-day modified Rankin Scale (mRS) score of 2 in all cases. CONCLUSIONS: We demonstrate that endovascular treatment for VITT-associated CVST is feasible and can be safe in cases that deteriorate despite medical therapy. Extensive clot burden, concomitant hemorrhage, rapid clinical progression and persistent rises in intracranial pressure should initiate multidisciplinary team discussion for endovascular treatment in appropriate cases.

Hematologic adverse events reported after COVID-19 vaccination in the Philippines: A national database study.

Vaccination is the most important strategy in preventing COVID-19. Vaccine efficacy and safety have been established in clinical trials but real-world data are useful to determine occurrence of adverse events in a population with heterogeneous characteristics. Knowledge on the hematologic events associated with different COVID-19 vaccines would be beneficial for patients as well as hematologists who oversee the care of these patients. This study aimed to determine the rates and outcomes of hematologic adverse events after COVID-19 vaccination in the Philippines. In this self-controlled case series, there were 268 individuals reported to have hematologic adverse events. Most received Comirnaty at 29.85%. Majority (62.31%) reported hematologic adverse events following the first dose of the vaccine. The overall event rate was 0.0182 per 10,000 vaccine doses; and lymphadenopathy was the most common hematologic adverse effect with a rate of 0.011 per 10,000 vaccine doses, followed by anemia at 0.0034 per 10,000 vaccine doses and thrombocytopenia at 0.0017 per 10,000 vaccine doses. Autoimmune cytopenias were also reported with an event rate of 0.0007 per 10,000 vaccine doses for ITP. One-hundred thirty two (49.25%) were fully recovered and 23.88% were recovering from hematologic adverse events as of the time of writing. The study showed a low rate of hematologic adverse events post COVID-19 vaccination with the seven different vaccine brands administered in the Philippines.

Potential mechanisms of vaccine-induced thrombosis.

Vaccine-induced immune thrombocytopenia and thrombosis (VITT) is a rare syndrome characterized by high-titer anti-platelet factor 4 (PF4) antibodies, thrombocytopenia and arterial and venous thrombosis in unusual sites, as cerebral venous sinuses and splanchnic veins. VITT has been described to occur almost exclusively after administration of ChAdOx1 nCoV-19 and Ad26.COV2.S adenovirus vector- based COVID-19 vaccines. Clinical and laboratory features of VITT resemble those of heparin-induced thrombocytopenia (HIT). It has been hypothesized that negatively charged polyadenylated hexone proteins of the AdV vectors could act as heparin to induce the conformational changes of PF4 molecule that lead to the formation of anti-PF4/polyanion antibodies. The anti-PF4 immune response in VITT is fostered by the presence of a proinflammatory milieu, elicited by some impurities found in ChAdOx1 nCoV-19 vaccine, as well as by soluble spike protein resulting from alternative splice events. Anti-PF4 antibodies bind PF4, forming immune complexes which activate platelets, monocytes and granulocytes, resulting in the VITT's immunothrombosis. The reason why only a tiny minority of patents receiving AdV-based COVID-19 vaccines develop VITT is still unknown. It has been hypothesized that individual intrinsic factors, either acquired (i.e., pre-priming of B cells to produce anti-PF4 antibodies by previous contacts with bacteria or viruses) or inherited (i.e., differences in platelet T-cell ubiquitin ligand-2 [TULA-2] expression) can predispose a few subjects to develop VITT. A better knowledge of the mechanistic basis of VITT is essential to improve the safety and the effectiveness of future vaccines and gene therapies using adenovirus vectors.

Kidney Transplantation from a Deceased Donor with COVID-19 Ad26.COV2-S Vaccine-Induced Thrombotic Thrombocytopenia.

BACKGROUND Vaccine-induced thrombosis and thrombocytopenia is a rare immune disorder documented after adenoviral vector ChAdOx1 nCOV-19 (AstraZeneca) and Ad26.COV2-S (Janssen) vaccine administration against severe acute respiratory syndrome coronavirus 2. It is a rare adverse effect with an incidence of 1 case per 100 000 exposures. The disorder represents altered immune response with proliferation of antibodies that bind to platelet factor 4 (PF4), leading to formation of thrombi and consumptive coagulopathy. Thrombosis combined with thrombocytopenia generally occurs in the first month following vaccination and can lead to fatal outcome, even in young, previously healthy individuals. These young adults ultimately may become solid organ donors. The main concerns with vaccine-induced thrombosis and thrombocytopenia solid organ donors are anti-PF4 antibodies transmission potential, risk of early major graft thrombosis, and serious bleeding. CASE REPORT In our center, 2 kidney transplantations were performed from a single brain-dead vaccine-induced thrombosis and thrombocytopenia donor following Ad26.COV2-S COVID-19 (Janssen) vaccine in October 2021, which represents the first 2 cases of kidney transplantation from a deceased vaccine-induced thrombosis and thrombocytopenia donor after immunization with Ad26.COV2-S (Janssen) vaccine. Both recipients were closely monitored in the early post-transplantation period and after discharge from the hospital. To date, both recipients have a good functioning allograft, without any evidence of vaccine-induced thrombosis and thrombocytopenia transmission. CONCLUSIONS Our results are consistent with those of previously published cases of successful vaccine-induced thrombosis and thrombocytopenia donor solid organ transplantation. Kidney allografts transplanted from vaccine-induced thrombosis and thrombocytopenia donors can have a good overall function with favorable outcomes.

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.

Vaccine-induced immune thrombotic thrombocytopenia post dose 2 ChAdOx1 nCoV19 vaccination: Less severe but remains a problem.

BACKGROUND: Vaccine-induced immune thrombotic thrombocytopenia (VITT) is a rare but established complication of 1st dose ChAdOx1 nCoV19 vaccination (AZD1222), however this complication after dose 2 remains controversial. OBJECTIVES: To describe the clinicopathological features of confirmed cases of VITT post dose 2 AZD1222 vaccination in Australia, and to compare this cohort to confirmed cases of VITT post 1st dose. METHODS: Sequential cases of clinically suspected VITT (thrombocytopenia, D-Dimer > 5x upper limit normal and thrombosis) within 4-42 days of dose 2 AZD1222 referred to Australia's centralised testing centre underwent platelet activation confirmatory testing in keeping with the national diagnostic algorithm. Final classification was assigned after adjudication by an expert advisory committee. Descriptive statistics were performed on this cohort and comparative analyses carried out on confirmed cases of VITT after 1st and 2nd dose AZD1222. RESULTS: Of 62 patients referred, 15 demonstrated presence of antibody mediated platelet activation consistent with VITT after dose 2 AZD1222. Four were immunoassay positive. Median time to presentation was 13 days (range 1-53) platelet count 116x10^9/L (range 63-139) and D-dimer elevation 14.5xULN (IQR 11, 26). Two fatalities occurred. In each, the dosing interval was less than 30 days. In comparison to 1st dose, dose 2 cases were more likely to be male (OR 4.6, 95% CI 1.3-15.8, p = 0.03), present with higher platelet counts (p = 0.05), lower D-Dimer (p = 01) and less likely to have unusual site thromboses (OR 0.14, 95% CI 0.04-0.28, p = 0.02). CONCLUSIONS: VITT is a complication of dose 2 AZD1222 vaccination. Whilst clinicopathological features are less severe, fatalities occurred in patients with concomitant factors.

Use of thrombopoietin receptor agonists in adults with immune thrombocytopenia: a systematic review and Central European expert consensus.

There are currently three thrombopoietin receptor agonists (TPO-RAs) approved in Europe for treating patients with immune thrombocytopenia (ITP): romiplostim (Nplate®), eltrombopag (Revolade®), and avatrombopag (Doptelet®). However, comparative clinical data between these TPO-RAs are limited. Therefore, the purpose of this study was to perform a literature review and seek expert opinion on the relevance and strength of the evidence concerning the use of TPO-RAs in adults with ITP. A systematic search was conducted in PubMed and Embase within the last 10 years and until June 20, 2022. A total of 478 unique articles were retrieved and reviewed for relevance. The expert consensus panel comprised ITP senior hematologists from eight countries across Central Europe. The modified Delphi method, consisting of two survey rounds, a teleconference and email correspondence, was used to reach consensus. Forty articles met the relevancy criteria and are included as supporting evidence, including five meta-analyses analyzing all three European-licensed TPO-RAs and comprising a total of 31 unique randomized controlled trials (RCTs). Consensus was reached on seven statements for the second-line use of TPO-RAs in the management of adult ITP patients. In addition, the expert panel discussed TPO-RA treatment in chronic ITP patients with mild/moderate COVID-19 and ITP patients in the first-line setting but failed to reach consensus. This work will facilitate informed decision-making for healthcare providers treating adult ITP patients with TPO-RAs. However, further studies are needed on the use of TPO-RAs in the first-line setting and specific patient populations.

Vaccine-induced immune thrombotic thrombocytopenia.

Within the first months of the COVID-19 vaccination campaign, previously healthy recipients who developed severe thrombosis (often cerebral and/or splanchnic vasculature) and thrombocytopenia typically after adenoviral vector-based vaccination were identified. Similarities between this syndrome, vaccine-induced immune thrombotic thrombocytopenia (VITT), and heparin-induced thrombocytopenia prompted recognition of the role of antiplatelet factor 4 (PF4) antibodies and management strategies based on IV immunoglobulin and nonheparin anticoagulants, which improved outcome. We update current understanding of VITT and potential involvement of anti-PF4 antibodies in thrombotic disorders.

Diagnostic Performance of a Particle Gel Immunoassay in Vaccine-Induced Immune Thrombotic Thrombocytopenia.

Vaccine-induced immune thrombotic thrombocytopenia (VITT) is a rare but serious complication of adenoviral vector-based COVID-19 vaccines. Similar to heparin-induced thrombocytopenia (HIT), antibodies reacting to platelet factor 4 (PF4) are responsible for platelet activation in VITT. The diagnosis of VITT includes the detection of anti-PF4 antibodies. Particle gel immunoassay (PaGIA) is one of the rapid immunoassays that is commonly used in the diagnosis of HIT to detect anti-PF4 antibodies. The aim of this study was to investigate the diagnostic performance of PaGIA in patients suspected of VITT. In this retrospective, single-center study, the correlation between PaGIA, enzyme immunoassay (EIA), and modified heparin-induced platelet aggregation assay (HIPA) in patients with findings suggestive of VITT was investigated. A commercially available PF4 rapid immunoassay (ID PaGIA H/PF4, Bio-Rad-DiaMed GmbH, Switzerland) and an anti-PF4/heparin EIA (ZYMUTEST HIA IgG, Hyphen Biomed) were used according to manufacturer's instructions. Modified HIPA was accepted as the gold standard test. Between March 8 and November 19, 2021, a total of 34 samples from clinically well-characterized patients (14 males, 20 females, mean age: 48.2 ± 18.2 years) were analyzed with PaGIA, EIA, and modified HIPA. VITT was diagnosed in 15 patients. Sensitivity and specificity of PaGIA were 54 and 67%, respectively. Anti-PF4/heparin optical density values were not significantly different between PaGIA positive and negative samples (p = 0.586). The sensitivity and specificity of EIA, on the other hand, were 87 and 100%, respectively. In conclusion, PaGIA is not reliable in the diagnosis of VITT because of its low sensitivity and specificity.

Increased incidence of immune thrombocytopenia (ITP) in 2021 correlating with the ongoing vaccination campaign against COVID-19 in a tertiary center - A monocentric analysis.

Immune thrombocytopenia (ITP) was reported as a rare complication of COVID-19 vaccines. We conducted a retrospective single-center analysis of all ITP cases detected in 2021 and compared the quantity with the pre-vaccination years, from 2018 to 2020. In 2021, a two-fold increase in ITP cases was identified compared to previous years; 11 of 40 cases (27.5%) were considered COVID-19-vaccine related. Our study highlights an increase in ITP cases at our institution, probably related to COVID-19 vaccinations. Further studies are needed to investigate this finding globally.

Autoimmune haemolytic anaemia and immune thrombocytopenia following SARS-CoV-2 and non-SARS-CoV-2 vaccination: 32 Years of passive surveillance data.

Autoimmune haemolytic anaemia (AIHA) and immune thrombocytopenia (ITP) are two uncommon haematologic autoimmune conditions that can rarely arise secondary to vaccination. Prior studies using the US Centers for Disease Control's (CDC) Vaccine Adverse Event Reporting System (VAERS) have demonstrated this infrequency, but contemporary data as well as comparison with current information regarding SARS-CoV-2 vaccination has not been assessed. In this study, we reviewed VAERS database reports from 1990 to 2022 to characterize the incidence and clinical and laboratory findings of non-SARS-CoV-2-associated AIHA and ITP and SARS-CoV-2 vaccine-associated AIHA and ITP. We discovered a total of 863 AIHA and ITP reports following vaccination with 15 non-SARS-CoV-2 and four SARS-CoV-2 vaccines submitted to the CDC VAERS database. AIHA and ITP reporting was low for both groups, with a large proportion excluded due to a lack of clinical details. ITP was reported the most frequently in both groups and was significantly more common with measles-mumps-rubella (MMR) vaccination (p < 0.001) in the non-SARS-CoV-2 group. AIHA and ITP cases were higher in the SARS-CoV-2 vaccine group, though ultimately still very infrequent. Autoimmune haematologic disease is vanishingly rare after immunization and rates are lower than in the general population according to passive reporting.

Decompressive surgery in cerebral venous sinus thrombosis due to vaccine-induced immune thrombotic thrombocytopenia.

BACKGROUND AND PURPOSE: Cerebral venous sinus thrombosis due to vaccine-induced immune thrombotic thrombocytopenia (CVST-VITT) is an adverse drug reaction occurring after severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccination. CVST-VITT patients often present with large intracerebral haemorrhages and a high proportion undergoes decompressive surgery. Clinical characteristics, therapeutic management and outcomes of CVST-VITT patients who underwent decompressive surgery are described and predictors of in-hospital mortality in these patients are explored. METHODS: Data from an ongoing international registry of patients who developed CVST within 28 days of SARS-CoV-2 vaccination, reported between 29 March 2021 and 10 May 2022, were used. Definite, probable and possible VITT cases, as defined by Pavord et al. (N Engl J Med 2021; 385: 1680-1689), were included. RESULTS: Decompressive surgery was performed in 34/128 (27%) patients with CVST-VITT. In-hospital mortality was 22/34 (65%) in the surgical and 27/94 (29%) in the non-surgical group (p < 0.001). In all surgical cases, the cause of death was brain herniation. The highest mortality rates were found amongst patients with preoperative coma (17/18, 94% vs. 4/14, 29% in the non-comatose; p < 0.001) and bilaterally absent pupillary reflexes (7/7, 100% vs. 6/9, 67% with unilaterally reactive pupil, and 4/11, 36% with bilaterally reactive pupils; p = 0.023). Postoperative imaging revealed worsening of index haemorrhagic lesion in 19 (70%) patients and new haemorrhagic lesions in 16 (59%) patients. At a median follow-up of 6 months, 8/10 of surgical CVST-VITT who survived admission were functionally independent. CONCLUSIONS: Almost two-thirds of surgical CVST-VITT patients died during hospital admission. Preoperative coma and bilateral absence of pupillary responses were associated with higher mortality rates. Survivors often achieved functional independence.