SARS-CoV-2 Vaccination-Induced Thrombotic Thrombocytopenia: A Rare but Serious Immunologic Complication.

Billions of individuals worldwide have benefited from the unprecedented large-scale rollout of COVID-19 vaccines. Given the sheer number of people that have received these vaccines, it is not surprising that rare side effects are reported that were not previously detected in the phase III vaccine trials. This review addresses one rare complication called SARS-CoV-2 vaccination-induced thrombotic thrombocytopenia (VITT). It occurs in approximately 1/50,000 to 1/100,000 recipients of the adenovirus vector-based COVID-19 vaccines made by AstraZeneca-Oxford or Johnson & Johnson. Information on VITT syndrome was disseminated quickly via social media and publications after it was first discovered. Initial observations associating VITT with specific patient populations, thrombus locations, and outcomes associated with heparin therapy have since been refined with additional clinical experience. In this review, we discuss what is currently known about the incidence, pathophysiology, diagnosis, and treatment of VITT.

Outcomes After Decompressive Surgery for Severe Cerebral Venous Sinus Thrombosis Associated or Not Associated with Vaccine-Induced Immune Thrombosis with Thrombocytopenia: A Multicenter Cohort Study.

BACKGROUND: Clinical observations indicated that vaccine-induced immune thrombosis with thrombocytopenia (VITT)-associated cerebral venous sinus thrombosis (CVST) often has a space-occupying effect and thus necessitates decompressive surgery (DS). While comparing with non-VITT CVST, this study explored whether VITT-associated CVST exhibits a more fulminant clinical course, different perioperative and intensive care unit management, and worse long-term outcome. METHODS: This multicenter, retrospective cohort study collected patient data from 12 tertiary centers to address priorly formulated hypotheses concerning the clinical course, the perioperative management with related complications, extracerebral complications, and the functional outcome (modified Rankin Scale) in patients with VITT-associated and non-VITT CVST, both with DS. RESULTS: Both groups, each with 16 patients, were balanced regarding demographics, kind of clinical symptoms, and radiological findings at hospital admission. Severity of neurological symptoms, assessed with the National Institute of Health Stroke Scale, was similar between groups at admission and before surgery, whereas more patients with VITT-associated CVST showed a relevant midline shift (≥ 4 mm) before surgery (100% vs. 68.8%, p = 0.043). Patients with VITT-associated CVST tended to undergo DS early, i.e., ≤ 24 h after hospital admission (p = 0.077). Patients with VITT-associated CVST more frequently received platelet transfusion, tranexamic acid, and fibrinogen perioperatively. The postoperative management was comparable, and complications were evenly distributed. More patients with VITT-associated CVST achieved a favorable outcome (modified Rankin Scale ≤ 3) at 3 months (p = 0.043). CONCLUSIONS: Although the prediction of individual courses remains challenging, DS should be considered early in VITT-associated CVST because an overall favorable outcome appears achievable in these patients.

SARS-CoV-2-related and Covid-19 vaccine-induced thromboembolic events: A comparative review.

Since the start of the pandemic, thrombotic events have been a well-known and severe complication associated with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. Nevertheless, the initiation of vaccination programs brought another rare yet highly fatal thrombotic event, vaccine-induced immune thrombotic thrombocytopaenia, which has caused extensive debate regarding the safety of vaccines. This review defines the thromboembolic events following infection and vaccination, identifies their risk factors, describes their pathophysiology, and discusses their management, treatment, and prevention.

Vaccine-induced immune thrombotic thrombocytopenia after vaccination against Covid-19: A clinical dilemma for clinicians and patients.

The coronavirus disease 2019 (Covid-19) pandemic has had devastating effects on public health worldwide, but the deployment of vaccines for Covid-19 protection has helped control the spread of SARS Coronavirus 2 (SARS-CoV-2) infection where they are available. The common side effects reported following Covid-19 vaccination were mostly self-restricted local reactions that resolved quickly. Nevertheless, rare vaccine-induced immune thrombotic thrombocytopenia (VITT) cases have been reported in some people being vaccinated against Covid-19. This review summarizes the thromboembolic events after Covid-19 vaccination and discusses its molecular mechanism, incidence rate, clinical manifestations and differential diagnosis. Then, a step-by-step algorithm for diagnosing such events, along with a management plan, are presented. In conclusion, considering the likeliness of acquiring severe SARS-CoV-2 infection and its subsequent morbidity and mortality, the benefits of vaccination outweigh its risks. Hence, if not already initiated, all governments should begin an effective and fast public vaccination plan to overcome this pandemic.

Letter to editor - observation on the article titled "Vaccine-Induced Thrombotic Thrombocytopenia (VITT): first report from India".

The first case of Vaccine-Induced Thrombotic Thrombocytopenia (VITT) was reported in the letter-to-editor submission in the journal of Indian Journal of Hematology and Blood Transfusion which was published online on 29th Sep 2021. Whereas, an article published in your journal on 04th Mar 2022 has been titled as first report of VITT from India which is a very conflicting statistic. The former article under reference has been diagnosed by a confirmatory functional assay as per the recommended guidelines and is thus genuinely the first case reported in this country.

Aortic thrombosis and acute limb ischemia after ChAdOx1 nCov-19 (Oxford-AstraZeneca) vaccination: a case of vaccine-induced thrombocytopenia and thrombosis (VITT).

INTRODUCTION: Vaccine-induced thrombocytopenia and thrombosis (VITT) is a rare but devastating adverse event associated with the ChAdOx1 nCoV-19 (Oxford-AstraZeneca) adenoviral vaccine against the Severe Acute Respiratory Syndrome CoronaVirus-2 (SARS-CoV-2). METHODS: A 49-year-old man presented to the emergency department with acute right limb ischemia (Rutherford IIB) nine days after his ChAdOx1 nCoV-19 (Oxford-AstraZeneca) vaccination. CT angiography revealed significant aortic thrombosis and right femoral artery occlusion. Severe thrombocytopenia (platelet count of 23 × 103/µL), promptly elevated D-dimers (37937 ng/mL) and a reduced fibrinogen level (176 mg/dL) were remarkable. ELISA testing for anti-PF4 antibodies confirmed the diagnosis of VITT. RESULTS: An emergency revascularization of the right leg was provided via thrombectomy. High-dose intravenous immunoglobulins were administered whereafter the platelet count restored gradually. Therapeutic anticoagulation was progressively started. The postoperative course was uneventful and follow-up imaging after four weeks showed an almost complete resolution of the significant aortic thrombosis. CONCLUSION: Early recognition and appropriate counseling of VITT is advocated to pursue a good clinical outcome. Our patient presenting with severe aortic thrombosis and acute limb ischemia was successfully treated by a vascular thrombectomy along with intravenous immunoglobulins and anticoagulation therapy as the mainstay therapy.

COVID-19: Vaccine-induced immune thrombotic thrombocytopenia.

In late February 2021, a prothrombotic syndrome was encountered for the first time in some of the recipients of ChAdOx1 CoV-19 vaccine (AstraZeneca, University of Oxford, and Serum Institute of India). Since the hallmark of this syndrome is the development of thrombocytopenia and/or thrombosis between 4 and 42 days after receiving a COVID-19 vaccine, it was named vaccine-induced immune thrombotic thrombocytopenia (VITT). Other names include "vaccine-induced prothrombotic immune thrombocytopenia" and "thrombosis with thrombocytopenia syndrome" by the Centers for Disease Control and the Food and Drug Administration (FDA). VITT appears similar to heparin-induced thrombocytopenia in that "platelet activating" autoantibodies are produced in both these conditions due to prior exposure of COVID-19 vaccine and heparin respectively, in turn causing thrombotic complications and consumptive thrombocytopenia. In this article, recent advances in the understanding of pathobiology, clinical features, investigative work-up, and management of VITT are reviewed.

Fatal vaccine-induced immune thrombotic thrombocytopenia (VITT) post Ad26.COV2.S: first documented case outside US.

PURPOSE: We reported the first described post Ad26.COV2.S (Janssen, Johnson & Johnson) vaccine-induced immune thrombocytopenia (VITT) case outside US.  CASE DESCRIPTION: CA young woman without any medical history presented association of deep vein thrombosis and thrombocytopenia at day 10 after vaccine injection. The patient was treated with low-molecular weight heparin at a first medical institution. Twelve days post Ad26.COV2.S vaccination, the patient was admitted at our hospital for neurological deterioration and right hemiplegia. Medical imaging using MRI showed thrombosis of the major anterior part of the sagittal superior sinus with bilateral intraparenchymal hemorrhagic complications. Screening tests for antibodies against platelet factor 4 (PF4)-heparin by rapid lateral flow immunoassay and chemiluminescence techniques were negative. Platelet activation test using heparin-induced multiple electrode aggregometry confirmed the initial clinical hypothesis. Despite immediate treatment with intravenous immunoglobulin, dexamethasone, danaparoid and attempted neurosurgery the patient evolved toward brain death. CONCLUSION: Even though it is an extremely rare complication of vaccination physicians should maintain a high index of suspicion of VITT in patients who received an adenovirus-vector-based SARS-CoV-2 vaccine within the last 30 days with persistent complains compatible with VITT or thromboembolic event associated with thrombocytopenia. The diagnosis should not be excluded if the rapid anti-PF4 immunological nor chemiluminescence techniques yield negative results. An adapted functional assay should be performed to confirm the diagnosis. Early treatment with intravenous immunoglobulin and non-heparin anticoagulants is essential as delayed diagnosis and administration of appropriate treatment is associated with poor prognosis.

Review and evolution of guidelines for diagnosis of COVID-19 vaccine induced thrombotic thrombocytopenia (VITT).

Coronavirus disease 2019 (COVID-19) is a life-threatening infectious disease caused by Severe acute respiratory syndrome Coronavirus-2 (SARS-CoV-2). In response to the still ongoing pandemic outbreak, a number of COVID-19 vaccines have been quickly developed and deployed. Although minor adverse events, either local (e.g., soreness, itch, redness) or systematic (fever, malaise, headache, etc.), are not uncommon following any COVID-19 vaccination, one rare vaccine-associated event can cause fatal consequences due to development of antibodies against platelet factor 4 (PF4), which trigger platelet activation, aggregation, and possible resultant thrombosis, often at unusual vascular sites. Termed thrombosis with thrombocytopenia syndrome (TTS) by reporting government agencies, the term vaccine-induced (immune) thrombotic thrombocytopenia (VITT) is more widely adopted by workers in the field. In response to increasing reports of VITT, several expert groups have formulated guidelines for diagnosis and/or management of VITT. Herein, we review some key guidelines related to diagnosis of VITT, and also provide some commentary on their development and evolution.

Experience of danaparoid to treat vaccine-induced immune thrombocytopenia and thrombosis, VITT.

BACKGROUND: Vaccine-induced immune thrombocytopenia and thrombosis (VITT) is triggered by nCOV-19 adenovirus-vectored vaccines against SARS-CoV2. Pathogenesis has been mainly related to platelet activation via PF4-reactive antibodies that activate platelets and may cross-react with heparin. Data concerning optimal anticoagulation are anecdotal, and so far, there are scattered reports of danaparoid use in VITT management. Danaparoid has good efficacy and safety in treatment of heparin-induced thrombocytopenia. We report here our experience of the administration and monitoring danaparoid in VITT. METHODS: We diagnosed a series of six hospitalized cases of VITT, based on the international diagnostic guidance. All VITT-related data were from the local electronic medical and laboratory record system and were analyzed with IBM SPSS Statistics. RESULTS: Predominately women in their late 40's developed VITT on average 24 days (range 9-59) after the first ChAdOx1 dose. Clinical presentation included single or multiple venous and/or arterial thrombosis, moderate thrombocytopenia and high D-dimer levels. After detecting PF4 antibodies subcutaneous danaparoid was our first-line antithrombotic treatment with an average duration of three weeks. The median plasma anti-FXa activity was in the lower part of the therapeutic range and during the first week of danaparoid administration clinical symptoms, platelet counts, and fibrin turnover resolved or significantly improved. The average duration of hospital admission was 10 days [2-18]. One patient died but the other five patients recovered completely. CONCLUSIONS: The clinical outcomes of our small cohort align with the earlier published reports, and support danaparoid as a rational option for the initial anticoagulation of VITT patients.

Platelet and extracellular vesicles in COVID-19 infection and its vaccines.

Platelets are at the crossroads between thrombosis and inflammation. When activated, platelets can shed bioactive extracellular vesicles [pEVs] that share the hemostatic potential of their parent cells and act as bioactive shuttles of their granular contents. In a viral infection, platelets are activated, and pEVs are generated with occasional virion integration. Both platelets and pEVs are engaged in a bidirectional interaction with neutrophils and other cells of the immune system and the hemostatic pathways. Severe COVID-19 infection is characterized by a stormy thromboinflammatory response with platelets and their EVs at the center stage of this reaction. This review sheds light on the interactions of platelets, pEVS and SARS-CoV-2 infection and prognostic and potential therapeutic role of pEVs. The review also describes the role of pEVs in the rare adenovirus-based COVID-19 vaccine-induced thrombosis thrombocytopenia.

Arterial intracranial thrombosis as the first manifestation of vaccine-induced immune thrombotic thrombocytopenia (VITT): a case report.

OBJECTIVE: We describe a severe case of vaccine-induced immune thrombotic thrombocytopenia (VITT) after the first dose of the ChAdOx1 nCoV-19 vaccine leading to massive ischemic stroke. METHODS: A 42-year-old woman developed acute left hemiparesis (NIHSS 12) 9 days after the first vaccine dose. RESULTS: The blood tests revealed low platelets (70 103/µL) and severe increment of D-dimer (70,745 ng/mL FEU). Brain non-contrast computed tomography and multiphasic CT angiography demonstrated a right middle cerebral artery occlusion. The patient was treated with primary thrombectomy, steroids, immunoglobulin, and fondaparinux. Despite the treatment, the neurological status deteriorated and underwent decompressive hemicraniectomy. She was transferred to the rehab's unit 52 days after the onset. DISCUSSION: Healthcare providers should be aware of the possibility of ischemic stroke as a manifestation of VITT. Awareness on this very rare and possibly fatal complication should be reinforced on both the vaccine recipients and general practitioners.

Massive cerebral venous sinus thrombosis in vaccine-induced immune thrombotic thrombocytopenia after ChAdOx1 nCoV-19 serum: case report of a successful multidisciplinary approach.

We report a case of massive cerebral venous sinus thrombosis in the contest of vaccine-induced immune thrombotic thrombocytopenia that required the rapid coordination of many specialists from different departments, notably emergency, neurology, neuroradiology, hematology, and neurosurgery. The patient was rapidly treated with steroids, immunoglobulin, and fondaparinux. She underwent within 6 h after hospital admission a mechanical thrombectomy in order to allow flow restoration in cerebral venous systems. Neuroendovascular treatment in cerebral venous thrombosis related to VITT has never been described before. It can represent a complementary tool along with the other therapies and a multidisciplinary approach.

Late-Onset Vaccine-Induced Immune Thombotic Thrombocytopenia (VITT) with Cerebral Venous Sinus Thrombosis.

OBJECTIVES: Vaccine-induced thrombotic thrombocytopenia (VITT) is a rare complication after adenoviral vector vaccination against COVID-19 reported up to 24 days after ChAdOx1 nCOV-19 (AZD1222) vaccination. This report describes a case with a significantly later onset of VITT with cerebral venous sinus thrombosis. CASE DESCRIPTION: We report a 42-year-old woman presenting to the emergency department 53 days after AZD1222 vaccination with sudden onset sensory aphasia and an 18-day history of headache. Cranial computed tomography (CT) showed acute intracranial hemorrhage and CT venogram demonstrated thrombosis of the left vein of Labbé and transverse and sigmoid sinus. D-dimers were elevated and despite a normal platelet count, platelet-activating anti-PF4 antibody testing was positive, confirming the diagnosis of VITT. The patient was treated with intravenous immunoglobulins and argatroban, and was discharged without any neurological deficit on day 12. CONCLUSION: Our report of VITT with symptom onset on day 35 and diagnosis of cerebral sinuous thrombosis on day 53 after AZD1222 vaccination significantly enhances the time window during which VITT may occur.

[Novel disease entities due to antiplatelet factor 4 antibodies: HIT, aHIT, and VITT].

Antiplatelet factor 4 (PF4) antibodies, also known as anti-PF4/heparin complex antibodies, are measured to diagnose heparin-induced thrombocytopenia (HIT). In HIT, anti-PF4 antibodies induced by heparin exposure cause thrombocytopenia and thrombosis. However, in recent years, autoimmune HIT (aHIT) that develops without heparin exposure has been getting attention. In 2021, anti-PF4 antibodies were reported to cause the fatal vaccine-induced immune thrombotic thrombocytopenia (VITT) that developed after adenoviral vector vaccination for COVID-19. HIT, aHIT, and VITT are considered to be caused by anti-PF4 antibodies, and their pathological conditions are similar. However, they have different levels of severity, and the detection sensitivity of their antibodies varies depending on the assay. Herein, we review three pathologies, namely, HIT, aHIT, and VITT, associated with anti-PF4 antibodies.

[Heparin-induced thrombocytopenia and vaccine-induced immune thrombotic thrombocytopenia: novel insights on anti-platelet factor 4 antibodies].

The levels of anti-platelet factor 4 (PF4) antibodies, also known as anti-PF4 or heparin complex antibodies, are used to diagnose heparin-induced thrombocytopenia (HIT). In HIT, anti-PF4 antibodies induced by heparin exposure cause thrombocytopenia and thrombosis. However, anti-PF4 antibodies were recently reported to be associated with the development of fatal vaccine-induced immune thrombotic thrombocytopenia (VITT) after adenoviral vector vaccination for coronavirus disease 2019. HIT and VITT are caused by anti-PF4 antibodies and have similar pathological conditions. However, the severity of these conditions differs and the detection sensitivity of their antibodies varies depending on the assays used. Herein, we review HIT and VITT associated with anti-PF4 antibodies.

Case of Suspected SARS-CoV-2 Vaccine-induced Immune Thrombotic Thrombocytopenia: Dilemma for Organ Donation.

Several vaccines were developed and rolled out at an unprecedented rate in response to the coronavirus disease-2019 (COVID-19) pandemic. Most vaccines approved globally by WHO for emergency use to combat the pandemic were deemed remarkably effective and safe. Despite the safety, rare incidences of vaccine-induced thrombosis and thrombocytopenia (VITT), sometimes known as vaccine-induced prothrombotic thrombocytopenia (VIPIT), have been reported. We report a case of young female with prothrombotic conditions and suspected VITT who developed catastrophic cerebral venous sinus thrombosis (CVST) and progressed to brain death. We highlight hurdles of organ retrieval from a brain-dead patient with suspected SARS-CoV-2 vaccine-induced immune thrombotic thrombocytopenia. There is limited data and lack of substantial evidence regarding transplantation of organs from brain-dead patients with suspected VITT. How to cite this article: Tiwari AM, Zirpe KG, Gurav SK, Bhirud LB, Suryawanshi RS, Kulkarni SS. Case of Suspected SARS-CoV-2 Vaccine-induced Immune Thrombotic Thrombocytopenia: Dilemma for Organ Donation. Indian J Crit Care Med 2022;26(4):514-517.

Mechanisms of Immunothrombosis in Vaccine-Induced Thrombotic Thrombocytopenia (VITT) Compared to Natural SARS-CoV-2 Infection.

Herein, we consider venous immunothrombotic mechanisms in SARS-CoV-2 infection and anti-SARS-CoV-2 DNA vaccination. Primary SARS-CoV-2 infection with systemic viral RNA release (RNAaemia) contributes to innate immune coagulation cascade activation, with both pulmonary and systemic immunothrombosis - including venous territory strokes. However, anti-SARS-CoV-2 adenoviral-vectored-DNA vaccines -initially shown for the ChAdOx1 vaccine-may rarely exhibit autoimmunity with autoantibodies to Platelet Factor-4 (PF4) that is termed Vaccine-Induced Thrombotic Thrombocytopenia (VITT), an entity pathophysiologically similar to Heparin-Induced Thrombocytopenia (HIT). The PF4 autoantigen is a polyanion molecule capable of independent interactions with negatively charged bacterial cellular wall, heparin and DNA molecules, thus linking intravascular innate immunity to both bacterial cell walls and pathogen-derived DNA. Crucially, negatively charged extracellular DNA is a powerful adjuvant that can break tolerance to positively charged nuclear histone proteins in many experimental autoimmunity settings, including SLE and scleroderma. Analogous to DNA-histone interactons, positively charged PF4-DNA complexes stimulate strong interferon responses via Toll-Like Receptor (TLR) 9 engagement. A chain of events following intramuscular adenoviral-vectored-DNA vaccine inoculation including microvascular damage; microbleeding and platelet activation with PF4 release, adenovirus cargo dispersement with DNA-PF4 engagement may rarely break immune tolerance, leading to rare PF4-directed autoimmunity. The VITT cavernous sinus cerebral and intestinal venous territory immunothrombosis proclivity may pertain to venous drainage of shared microbiotal-rich areas of the nose and in intestines that initiates local endovascular venous immunity by PF4/microbiotal engagement with PF4 autoantibody driven immunothrombosis reminiscent of HIT. According to the proposed model, any adenovirus-vectored-DNA vaccine could drive autoimmune VITT in susceptible individuals and alternative mechanism based on molecular mimicry, vaccine protein contaminants, adenovirus vector proteins, EDTA buffers or immunity against the viral spike protein are secondary factors. Hence, electrochemical DNA-PF4 interactions and PF4-heparin interactions, but at different locations, represent the common denominator in HIT and VITT related autoimmune-mediated thrombosis.

Postmortem investigation of fatalities following vaccination with COVID-19 vaccines.

Thorough postmortem investigations of fatalities following vaccination with coronavirus disease 2019 (COVID-19) vaccines are of great social significance. From 11.03.2021 to 09.06.2021, postmortem investigations of 18 deceased persons who recently received a vaccination against COVID-19 were performed. Vaxzevria was vaccinated in nine, Comirnaty in five, Spikevax in three, and Janssen in one person. In all cases, full autopsies, histopathological examinations, and virological analyses for the severe acute respiratory syndrome coronavirus 2 were carried out. Depending on the case, additional laboratory tests (anaphylaxis diagnostics, VITT [vaccine-induced immune thrombotic thrombocytopenia] diagnostics, glucose metabolism diagnostics) and neuropathological examinations were conducted. In 13 deceased, the cause of death was attributed to preexisting diseases while postmortem investigations did not indicate a causal relationship to the vaccination. In one case after vaccination with Comirnaty, myocarditis was found to be the cause of death. A causal relationship to vaccination was considered possible, but could not be proven beyond doubt. VITT was found in three deceased persons following vaccination with Vaxzevria and one deceased following vaccination with Janssen. Of those four cases with VITT, only one was diagnosed before death. The synopsis of the anamnestic data, the autopsy results, laboratory diagnostic examinations, and histopathological and neuropathological examinations revealed that VITT was the very likely cause of death in only two of the four cases. In the other two cases, no neuropathological correlate of VITT explaining death was found, while possible causes of death emerged that were not necessarily attributable to VITT. The results of our study demonstrate the necessity of postmortem investigations on all fatalities following vaccination with COVID-19 vaccines. In order to identify a possible causal relationship between vaccination and death, in most cases an autopsy and histopathological examinations have to be combined with additional investigations, such as laboratory tests and neuropathological examinations.

Platelet factor 4 polyanion immune complexes: heparin induced thrombocytopenia and vaccine-induced immune thrombotic thrombocytopenia.

BACKGROUND: This is a review article on heparin-induced thrombocytopenia, an adverse effect of heparin therapy, and vaccine-induced immune thrombotic thrombocytopenia, occurring in some patients administered certain coronavirus vaccines. MAIN BODY/TEXT: Immune-mediated thrombocytopenia occurs when specific antibodies bind to platelet factor 4 /heparin complexes. Platelet factor 4 is a naturally occurring chemokine, and under certain conditions, may complex with negatively charged molecules and polyanions, including heparin. The antibody-platelet factor 4/heparin complex may lead to platelet activation, accompanied by other cascading reactions, resulting in cerebral sinus thrombosis, deep vein thrombosis, lower limb arterial thrombosis, myocardial infarction, pulmonary embolism, skin necrosis, and thrombotic stroke. If untreated, heparin-induced thrombocytopenia can be life threatening. In parallel, rare incidents of spontaneous vaccine-induced immune thrombotic thrombocytopenia can also occur in some patients administered certain coronavirus vaccines. The role of platelet factor 4 in vaccine-induced thrombosis with thrombocytopenia syndrome further reinforces the importance the platelet factor 4/polyanion immune complexes and the complications that this might pose to susceptible individuals. These findings demonstrate, how auxiliary factors can complicate heparin therapy and drug development. An increasing interest in biomanufacturing heparins from non-animal sources has driven a growing interest in understanding the biology of immune-mediated heparin-induced thrombocytopenia, and therefore, the development of safe and effective biosynthetic heparins. SHORT CONCLUSION: In conclusion, these findings further reinforce the importance of the binding of platelet factor 4 with known and unknown polyanions, and the complications that these might pose to susceptible patients. In parallel, these findings also demonstrate how auxiliary factors can complicate the heparin drug development.