The role of platelet factor 4, antibodies and platelets in adverse reactions after vaccination against SARS-CoV-2 and in other thrombotic complications

用腺病毒载体疫苗接种严重急性呼吸综合征冠状病毒-2 （SARS-CoV-2）疫苗可在接种后5至20天开始引起不寻常的血栓形成并伴有血小板减少症。这种疫苗诱导的免疫性血栓性血小板减少症（VITT）与针对血小板趋化因子血小板因子4 （PF4）的高滴度免疫球蛋白G （IgG）抗体相关。与PF4结合的抗PF4- igg通过血小板fc - γ iia受体激活血小板。VITT与自身免疫性肝素诱导的血小板减少症有密切的相似之处，这是我们小组的主要研究重点。最近，我们发现了几名原因不明的复发性血栓患者，他们具有独立于Covid - 19疫苗的相同抗体。我们的目标是通过表征VITT患者抗体反应的时间谱来解决针对PF4引起的VITT的病理性免疫反应。分析vitt患者的抗pf4 IgG亚类、克隆性和糖基化状态。针对PF4的免疫应答很可能是由疫苗的腺病毒成分触发的。因此，将确定并比较PF4在载体疫苗、完全载体病毒和其他病毒种中的结合伙伴。我们的初步数据强烈表明，与VITT中PF4表位结合的抗PF4抗体是导致严重复发性血栓形成的原因。我们生成了一种有助于区分hit样抗体和vitt样抗体的检测方法。我们将进一步分析细胞培养中腺病毒载体与巨核细胞的相互作用，旨在揭示接种mRNA SARS-CoV2疫苗后5-20天发生血栓形成和血小板减少的潜在机制。表征抗pf4 IgG介导的VITT免疫血栓形成机制将为VITT患者的新治疗理念奠定基础，但也可能启发Covid - 19患者免疫血栓形成机制，其中IgG介导的血小板活化类似。最后，我们的目标是建立VITT特异性小鼠模型。

Vaccination against severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) with adenoviral vector-based vaccines can cause unusual thrombosis in combination with thrombocytopenia beginning 5 to 20 days after vaccination. This vaccine-induced immune thrombotic thrombocytopenia (VITT) is associated with high-titer immunoglobulin G (IgG) antibodies directed against the platelet chemokine platelet factor 4 (PF4). Anti-PF4-IgG bound to PF4 activates platelets via platelet FcγIIa receptors. VITT shares close similarities with autoimmune heparin induced thrombocytopenia, a major research focus of our group. Very recently we identified several patients with recurrent thrombosis of unknown cause who have the same antibodies independent of Covid 19 vaccination. We aim to address the pathological immune response against PF4 causing VITT by characterizing the temporal profile of the antibody response in VITT patients. Anti-PF4 IgG from VITT-patients will be analysed for their IgG subclass, clonality and glycosylation status. It is likely that the immune response against PF4 is triggered by the adenoviral component of the vaccine. Hence, binding partners for PF4 in vector-based vaccines, complete vector viruses and other virus species will be identified and compared. Our preliminary data strongly indicate that anti-PF4 antibodies binding to the same epitope on PF4 as in VITT are the cause for severe recurrent thrombosis. We generate an assay facilitating differentiation between HIT-like and VITT-like antibodies. We will further analyse the interaction of adenoviral vectors with megakaryocytes in cell culture and aim to unravel the underlying mechanim of thrombosis and thrombocytopenia occurring 5-20 days after vaccination with mRNA SARS-CoV2 vaccines. The characterisation of the anti-PF4 IgG mediated mechanisms of immunothrombosis in VITT will build the cornerstone of new treatment concepts of patients with VITT, but may also enlight mechanisms of immunothrombosis in patients with Covid 19, where IgG-mediated platelet activation is similarly observed. Finally, we aim to establish a VITT specific mouse model.