Alterations in B- and circulating T-follicular helper cell subsets in immune thrombotic thrombocytopenic purpura

Anti-ADAMTS13 Autoantibodies in Immune-Mediated Thrombotic Thrombocytopenic Purpura

Autoantibodies to ADAMTS13 are at the center of pathology of the immune-mediated thrombotic thrombocytopenic purpura. These autoantibodies can be either inhibitory (enzymatic function) or non-inhibitory, resulting in protein depletion. Under normal physiologic conditions, antibodies are generated in response to foreign antigens, which can include infectious agents; however, these antibodies may at times cross-react with self-epitopes. This is one of the possible mechanisms mediating formation of anti-ADAMTS13 autoantibodies. The process known as "antigenic mimicry" may be responsible for the development of these autoantibodies that recognize and bind cryptic epitopes in ADAMTS13, disrupting its enzymatic function over ultra large von Willebrand factor multimers, forming the seeds for platelet activation and microthrombi formation. In particular, specific amino acid sequences in ADAMTS13 may lead to conformational structures recognized by autoantibodies. Generation of these antibodies may occur more frequently among patients with a genetic predisposition. Conformational changes in ADAMTS13 between open and closed states can also constitute the critical change driving either interactions with autoantibodies or their generation. Nowadays, there is a growing understanding of the role that autoantibodies play in ADAMTS13 pathology. This knowledge, especially of functional qualitative differences among antibodies and the ADAMTS13 sequence specificity of such antibodies, may make possible the development of targeted therapeutic agents to treat the disease. This review aims to present what is known of autoantibodies against ADAMTS13 and how their structure and function result in disease.

Challenges in managing iTTP: insights into ADAMTS13 inhibitor boosting during caplacizumab therapy

Immune-mediated thrombotic thrombocytopenic purpura (iTTP) is a rare but life-threatening disorder characterized by severe thrombocytopenia, hemolytic anemia, and end-organ ischemic damage. The introduction of caplacizumab, an anti-von Willebrand factor A1 nanobody, has revolutionized the treatment of patients with iTTP by preventing fatal thrombotic events and shortening the time to platelet normalization. Despite its benefits, caplacizumab does not address the challenge of anti-ADAMTS13 autoantibody production, posing a risk of ADAMTS13 inhibitor boosting and delayed recovery of ADAMTS13 activity. Here, we highlight three challenging cases from the Japanese TTP registry involving patients with iTTP who experienced severe ADAMTS13 inhibitor boosting. This delayed the recovery of ADAMTS13, and extended administration of caplacizumab while requiring additional therapeutic plasma exchange (TPE) and immunosuppressive therapy. All patients demonstrated delayed recovery of ADAMTS13 activity despite initial clinical improvement. Prolonged use of caplacizumab masked the persistence of ADAMTS13 inhibitors, emphasizing the need for close monitoring and timely interventions. Although recent proposals for TPE-free regimens show promise, our findings underscore that TPE remains essential for removing residual autoantibodies and preventing disease exacerbation in certain patients. Stratifying patients based on initial ADAMTS13 inhibitor titers and optimizing immunosuppressive strategies may help identify those at risk of severe inhibitor boosting. Further research is required to refine treatment protocols and ensure the safe withdrawal of caplacizumab while achieving sustained recovery of ADAMTS13 activity.

Pathological Mechanisms and Novel Testing Methods in Thrombotic Thrombocytopenic Purpura

Thrombotic thrombocytopenic purpura (TTP) is an uncommon, but potentially disabling or even deadly, thrombotic microangiopathy with a well-studied mechanism of ADAMTS13 deficiency or dysfunction. While established treatments are largely effective, the standard ADAMTS13 testing required to definitively diagnose TTP may cause delays in diagnosis and treatment, highlighting the need for rapid and effective diagnostic methods. Additionally, the heterogeneous presentation and varied inciting events of TTP suggest more variation in its mechanism than previously thought, implying three potential pathways rather than the accepted two. The recent discovery of ADAMTS13 conformation as a potential contributor to TTP in addition to the proposal of using the absolute immature platelet count (A-IPC) as a biomarker, present novel areas for monitoring and treatment. A-IPC in particular may serve as a more rapid and accurate diagnostic test to distinguish TTP from non-TTP TMAs and to monitor treatment response and relapse. These considerations highlight the need to further study TTP in order to improve best practices and patient care.

The differentiation courses of the Tfh cells: a new perspective on autoimmune disease pathogenesis and treatment

The follicular helper T cells are derived from CD4+T cells, promoting the formation of germinal centers and assisting B cells to produce antibodies. This review describes the differentiation process of Tfh cells from the perspectives of the initiation, maturation, migration, efficacy, and subset classification of Tfh cells, and correlates it with autoimmune disease, to provide information for researchers to fully understand Tfh cells and provide further research ideas to manage immune-related diseases.

Anti-ADAMTS13 Autoantibodies: From Pathophysiology to Prognostic Impact-A Review for Clinicians

Thrombotic thrombocytopenic purpura (TTP) is a fatal disease in which platelet-rich microthrombi cause end-organ ischemia and damage. TTP is caused by markedly reduced ADAMTS13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13) activity. ADAMTS13 autoantibodies (autoAbs) are the major cause of immune TTP (iTTP), determining ADAMTS13 deficiency. The pathophysiology of such autoAbs as well as their prognostic role are continuous objects of scientific studies in iTTP fields. This review aims to provide clinicians with the basic information and updates on autoAbs' structure and function, how they are typically detected in the laboratory and their prognostic implications. This information could be useful in clinical practice and contribute to future research implementations on this specific topic.