Laboratory approach for vaccine-induced thrombotic thrombocytopenia diagnosis in the Netherlands.

BACKGROUND AND OBJECTIVES: Vaccine-induced thrombotic thrombocytopenia (VITT) is a rare adverse effect characterized by thrombocytopenia and thrombosis occurring after COVID-19 vaccination. VITT pathophysiology is not fully unravelled but shows similarities to heparin-induced thrombocytopenia (HIT). HIT is characterized by the presence of antibodies against platelet factor 4 (PF4)/heparin complex, which can activate platelets in an FcγRIIa-dependent manner, whereas IgG-antibodies directed against PF4 play an important role in VITT. MATERIALS AND METHODS: We characterized all clinically suspected VITT cases in the Netherlands from a diagnostic perspective and hypothesized that patients who developed both thrombocytopenia and thrombosis display underlying mechanisms similar to those in HIT. We conducted an anti-PF4 ELISA and a functional PF4-induced platelet activation assay (PIPAA) with and without blocking the platelet-FcγRIIa and found positivity in both tests, suggesting VITT with mechanisms similar to those in VITT. RESULTS: We identified 65 patients with both thrombocytopenia and thrombosis among 275 clinically suspected VITT cases. Of these 65 patients, 14 (22%) tested positive for anti-PF4 and PF4-dependent platelet activation. The essential role of platelet-FcγRIIa in VITT with mechanisms similar to those in HIT was evident, as platelet activation was inhibited by an FcγRIIa-blocking antibody in all 14 patients. CONCLUSION: Our study shows that only a small proportion of clinically suspected VITT patients with thrombocytopenia and thrombosis have anti-PF4-inducing, FcɣRIIa-dependent platelet activation, suggesting an HIT-like pathophysiology. This leaves the possibility for the presence of another type of pathophysiology ('non-HIT like') leading to VITT. More research on pathophysiology is warranted to improve the diagnostic algorithm and to identify novel therapeutic and preventive strategies.

A Role of Effector CD 8 + T Cells Against Circulating Tumor Cells Cloaked with Platelets: Insights from a Mathematical Model.

Cancer metastasis accounts for a majority of cancer-related deaths worldwide. Metastasis occurs when the primary tumor sheds cells into the blood and lymphatic circulation, thereby becoming circulating tumor cells (CTCs) that transverse through the circulatory system, extravasate the circulation and establish a secondary distant tumor. Accumulating evidence suggests that circulating effector CD 8 + T cells are able to recognize and attack arrested or extravasating CTCs, but this important antitumoral effect remains largely undefined. Recent studies highlighted the supporting role of activated platelets in CTCs's extravasation from the bloodstream, contributing to metastatic progression. In this work, a simple mathematical model describes how the primary tumor, CTCs, activated platelets and effector CD 8 + T cells participate in metastasis. The stability analysis reveals that for early dissemination of CTCs, effector CD 8 + T cells can present or keep secondary metastatic tumor burden at low equilibrium state. In contrast, for late dissemination of CTCs, effector CD 8 + T cells are unlikely to inhibit secondary tumor growth. Moreover, global sensitivity analysis demonstrates that the rate of the primary tumor growth, intravascular CTC proliferation, as well as the CD 8 + T cell proliferation, strongly affects the number of the secondary tumor cells. Additionally, model simulations indicate that an increase in CTC proliferation greatly contributes to tumor metastasis. Our simulations further illustrate that the higher the number of activated platelets on CTCs, the higher the probability of secondary tumor establishment. Intriguingly, from a mathematical immunology perspective, our simulations indicate that if the rate of effector CD 8 + T cell proliferation is high, then the secondary tumor formation can be considerably delayed, providing a window for adjuvant tumor control strategies. Collectively, our results suggest that the earlier the effector CD 8 + T cell response is enhanced the higher is the probability of preventing or delaying secondary tumor metastases.

Platelets in Kawasaki disease: mediators of vascular inflammation.

Kawasaki disease, a systemic vasculitis that affects young children and can result in coronary artery aneurysms, is the leading cause of acquired heart disease among children. A hallmark of Kawasaki disease is increased blood platelet counts and platelet activation, which is associated with an increased risk of developing resistance to intravenous immunoglobulin and coronary artery aneurysms. Platelets and their releasate, including granules, microparticles, microRNAs and transcription factors, can influence innate immunity, enhance inflammation and contribute to vascular remodelling. Growing evidence indicates that platelets also interact with immune and non-immune cells to regulate inflammation. Platelets boost NLRP3 inflammasome activation and IL-1ß production by human immune cells by releasing soluble mediators. Activated platelets form aggregates with leukocytes, such as monocytes and neutrophils, enhancing numerous functions of these cells and promoting thrombosis and inflammation. Leukocyte-platelet aggregates are increased in children with Kawasaki disease during the acute phase of the disease and can be used as biomarkers for disease severity. Here we review the role of platelets in Kawasaki disease and discuss progress in understanding the immune-effector role of platelets in amplifying inflammation related to Kawasaki disease vasculitis and therapeutic strategies targeting platelets or platelet-derived molecules.

Aplicación de las plaquetas en la extrofia vesical / Use of platelet in bladder exstrophy

La extrofia vesical es una anomalía congénita grave del tracto urinario inferior que afecta la vejiga, los huesos pelvianos, la pared abdominal, los genitales externos, el perineo y, en algunos casos, el intestino. Los tratamientos convencionales están basados en técnicas quirúrgicas, para lograr reconstruir la vejiga, los genitales y cerrar el defecto de la pared. Se presenta el caso de una niña de 3 años de edad, en la que el tratamiento quirúrgico se había aplicado en 6 ocasiones sin resultados. Se decidió combinar el tratamiento quirúrgico con la aplicación de medicina regenerativa. Se le aplicó lisado de plaquetas en la pared de la vejiga y los bordes de la pared abdominal a razón de 1 mL semanal, durante 4 semanas. Se logró la regeneración de los tejidos que permitió afrontar los bordes de dichas estructuras y realizar la técnica quirúrgica convencional. Como resultado se logró cierre total de vejiga, uretra y pared abdominal, sin fístulas entre estas estructuras ni al exterior. La utilización del lisado de plaquetas favorece el crecimiento y regeneración de los tejidos que componen el tracto urinario. La cirugía puede ser una solución definitiva, después de haber aplicado los factores de crecimiento plaquetarios, que preparan el tejido en cuanto a calidad y cantidad, favoreciendo el afrontamiento de los bordes, la cicatrización y disminuyendo las complicaciones posquirúrgicas(AU)

Bladder exstrophy is a severe congenital anomaly of lower urinary tract that affects the bladder, pelvic bones, abdominal wall, external genitalia, perineum and in some cases intestine. Conventional treatments are based on surgical techniques, in order to reconstruct bladder, genitals and close wall defect. We present a case of a 3 year old girl, in which surgical treatment was applied 6 times without results. It was decided to combine the surgical treatment with application of regenerative medicine. It was applied platelet lysate in the bladder wall and the edges of the abdominal wall at the rate of 1 mL weekly for 4 weeks, achieving tissue regeneration. It enabled to face the edges of those structures and perform conventional surgical technique. As a result, we achieved a total closure of bladder, urethra and abdominal wall, without fistulas either between these structures or outside. Therefore the use of platelet lysate promotes growth and tissue regeneration comprising the urinary tract, decreasing number of interventions, time exposition structures of the abdominal cavity, and post surgical complications such as fistulas(AU)