The Paradox of Platelet Activation and Impaired Function in Primary Myelofibrosis: In Vivo and Ex Vivo Platelet Function Study

Primary myelofibrosis (PMF) is a myeloproliferative neoplasm characterized by shortened survival. Thrombosis can be a risk factor associated with inferior survival. In PMF this risk factor is poorly studied. Clonal hematopoiesis and circulating free DNA (cfDNA) activate the platelets in PMF. It is reported that activated platelets recirculate as exhausted defective platelets with impaired function on ex vivo analysis. In PMF the studies on ex vivo platelet function are missing. Therefore, we studied P-selectin (CD62P) expression, as marker of in vivo platelet function, and the PFA (platelet function assay)-100, as marker of ex vivo platelet function. In addition, we measured the vWF ristocetin cofactor(vWF:Rco)/von Willebrand antigen (vWF:Ag) ratio. The study included 27 patients diagnosed with PMF according to WHO/ICC 2022 criteria. Patients were 46 years old (28-71 years). The mean duration of disease was 8 years (1-20 years). Nobody was on cytoreduction or antiplatelet. Nobody had thrombotic risk factors. Of 27patients, 21/27 were JAK2 mutated with variant allele frequency (VAF) of 50% and 6/27 CALR mutated with VAF of 51%. 19/27 were low- and 8/27 intermediate-1 risk IPSS. 30 healthy served as control. The mutations were conducted by ARMS-PCR gel electrophoresis. Cell blood counts (CBCs) were measured by automated analyzer. P-selectin was measured by flow cytometry and PFA-100 was measured on Collagen/ADP (CT-ADP) and Collagen/Epinephrine (CT/EPI) cartridges. vWF:Rco/vWF:Ag ratio was measured by latex immunoassay. CBCs were normal in all patients.All patients had hjgh P-selectin (45±3% vs 10±5%) and prolonged closure time (CT) of C/ADP (C/ADP, n.v. 68-121 s (144±20 s vs 90±10 s) and C/EPI (n.v. 84-160 s (241±20 s vs 95±15 s) (p<0.05). Interstingly, we found abnormal (<0.6) values of vWF:Rco/vWF:Ag ratio consistent with the prolonged CT. No difference there was with regards to the occurrence of JAK2 or CALR mutations. We speculate that PFA-100 might be a test of choice to show the hyperactivation of the patelets in PMF. Hence, could be suggested the primary prophylaxis with aspirin currently debated in PMF. Further studies are warranted and necessary.

No relevant conflicts of interest to declare.