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In the last years, the use of thrombopoietin receptor agonists (TPO-RA), eltrombopag and romiplostim, has improved the management of immune thrombocytopenia (ITP). Moreover, eltrombopag is also active in patients with aplastic anemia and myelodysplastic syndrome. However, their mechanisms of action and signaling pathways still remain controversial. In order to gain insight into the mechanisms underlying eltrombopag therapy, a gene expression profile (GEP) analysis in patients treated with this drug was carried out. Fourteen patients with chronic ITP were studied by means of microarrays before and during eltrombopag treatment. Median age was 78 years (range, 35-87 years); median baseline platelet count was 14 × 10 9 /L (range, 2-68 × 10 9 /L). Ten patients responded to the therapy, two cases relapsed after an initial response and the remaining two were refractory to the therapy. Eltrombopag induced relevant changes in the hematopoiesis, platelet activation and degranulation, as well as in megakaryocyte differentiation, with overexpression of some transcription factors and the genes PPBP, ITGB3, ITGA2B, F13A1, F13A1, MYL9 and ITGA2B . In addition, GP1BA, PF4, ITGA2B, MYL9, HIST1H4H and HIST1H2BH , genes regulated by RUNX1 were also significantly enriched after eltrombopag therapy. Furthermore, in non-responder patients, an overexpression of Bcl-X gene and genes involved in erythropoiesis, such as SLC4A1 and SLC25A39 , was also observed. To conclude, overexpression in genes involved in megakaryopoiesis, platelet adhesion, degranulation and aggregation was observed in patients treated with eltrombopag. Moreover, an important role regarding heme metabolism was also present in non-responder patients.

The RASGRP2 gene encodes the Ca 2+ and DAG-regulated guanine nucleotide exchange factor I (CalDAG-GEFI), which plays a key role in integrin activation in platelets and neutrophils. We here report two new RASGRP2 variants associated with platelet dysfunction and bleeding in patients. The homozygous patients had normal platelet and neutrophil counts and morphology. Platelet phenotyping showed: prolonged PFA-100 closure times; normal expression of major glycoprotein receptors; severely reduced platelet aggregation response to ADP and collagen (both patients); aggregation response to PAR1 and arachidonic acid markedly impaired in one patient; PMA-induced aggregation unaffected; platelet secretion, clot retraction, and spreading minimally affected. Genetic analysis identified two new homozygous variants in RASGRP2: c.706C>T (p.Q236X) and c.887G>A (p.C296Y). In both patients, CalDAG-GEFI protein was not detectable in platelet lysates, and platelet αIIbβ3 activation, as assessed by fibrinogen binding, was greatly impaired in response to all agonists except PMA. Patient neutrophils showed normal integrin expression, but impaired Mn 2+ -induced fibrinogen binding. In summary, we have identified two new RASGRP2 mutations that can be added to this rapidly growing form of inherited platelet function disorder.

Eltrombopag is effective and safe in chronic immune thrombocytopenia (ITP) patients not responding to previous therapy. However, when eltrombopag is discontinued, platelet counts usually return to baseline within 2 weeks. Here, we describe the clinical characteristics of the, to the best of our knowledge, largest case series of patients with ITP, who presented sustained responses after discontinuing eltrombopag (n = 12). The median time from diagnosis to eltrombopag initiation was 24 months (range, 1-480). The median number of prior therapies was 5 (range, 1-7), and the median duration of eltrombopag treatment was 5 months (range, 1-13). Three patients received eltrombopag for only 1 month. The treatment was well-tolerated. The median (range) follow-up of this case series was of 7 months (6-20), during which all patients maintained a safe platelet count without the need for anti-ITP treatment. The communication of such cases may support the conduction of new studies to investigate which predictive factors could identify ITP patients with sustained responses after discontinuing eltrombopag without additional therapy. The need of long-term use of eltrombopag should be re-examined.