Clonal endothelial progenitor cells (EPCs) have been implicated in the aberrant vascular growth that features infantile hemangioma (IH), the most common benign vascular tumor in childhood that may cause ulceration, bleeding, and/or permanent disfigurement. Endothelial colony-forming cells (ECFCs), truly endothelial EPCs endowed with clonal ability and capable of forming patent vessels in vivo, remodel their Ca ²⁺ toolkit in tumor-derived patients to acquire an adaptive advantage. Particularly, they upregulate the proangiogenic store-operated Ca ²⁺ entry (SOCE) pathway due to the overexpression of its underlying components, that is, stromal interaction molecule 1 (Stim1), Orai1, and transient receptor potential canonical 1 (TRPC1). The present work was undertaken to assess whether and how the Ca ²⁺ signalosome is altered in IH-ECFCs by employing Ca ²⁺ and nitric oxide (NO) imaging, real-time polymerase chain reaction, western blotting, and functional assays. IH-ECFCs display a lower intracellular Ca ²⁺ release in response to either pharmacological (i.e., cyclopiazonic acid) or physiological (i.e., ATP and vascular endothelial growth factor) stimulation. Conversely, Stim1, Orai1, and TRPC1 transcripts and proteins are normally expressed in these cells and mediate a constitutive SOCE, which is sensitive to BTP-2, La ³⁺ , and Pyr6 and recharges the intracellular Ca ²⁺ pool. The resting SOCE in IH-ECFCs is also associated to an increase in their proliferation rate and the basal production of NO compared to normal cells. Likewise, the pharmacological blockade of SOCE and NO synthesis block IH-ECFC growth. Collectively, these data indicate that the constitutive SOCE activation enhances IH-ECFC proliferation by augmenting basal NO production and sheds novel light on the molecular mechanisms of IH.

Kawasaki disease (KD) is rare in infants less than 3 months of age, and its recurrence is exceptional. Infants with KD are at higher risk of severe clinical presentation, therapy failure, complications and coronary aneurysms (CAAs), and this is the reason they deserve more aggressive therapy and a strict clinical follow-up. We report a 2-month-old male with KD, complicated by Macrophage Activation Syndrome (MAS). Despite timely and aggressive therapy with immunoglobulins, steroids and aspirin, multiple CAAs developed. Two-month therapy with anakinra completely reverted all the aneurysms. After six months, the infant experienced KD relapse and was successfully re-treated with immunoglobulins, steroids and aspirin. A strict echocardiographic follow-up did not show recurrence of aneurysms. Two years later, the child is healthy, without cardiac sequelae. In our experience, anakinra was effective in reverting multiple aneurysms and its effect proved to be long-lasting, even in front of KD recurrence. Based on this evidence, it seems reasonable to hypothesize not to limit the use of anakinra as rescue therapy for complicated or refractory KD, but to consider the possibility of adding it to first-line therapies for some subgroups of very-high-risk patients, in order to strengthen the prevention of CAAs.

Endothelial progenitor cells (EPCs) have been suggested to contribute to the neovascularization of infantile haemangioma (IH). There is strong evidence of the efficacy of propranolol in the treatment of IH, possibly by inhibiting both vasculogenesis and angiogenesis in the tumour. We evaluate the frequency of circulating endothelial colony forming cells (ECFCs), as the best EPC surrogate, in patients with IH at diagnosis and while receiving propranolol by an ex vivo 12-month longitudinal study. Biological aspects of the ECFCs, such as their in vitro angiogenic potential, membrane CXCR4 expression and Ca²⁺ signalling, were investigated. Circulating ECFCs were isolated by in vitro culture and expanded for 2 to 3 passages in 23 patients with IH (median age: 5.5 months, range: 5.5 weeks–11 months) before and 3, 6, 9 and 12 months after receiving propranolol. Twenty-four healthy subjects comparable for age were also assessed (CTRLs). Untreated patients with IH had a circulating ECFC frequency lower (p = 0.001) than CTRLs; nevertheless, in in vitro starving conditions, ECFCs showed enhanced capacity to form tube-like structures than those of CTRLs. Patients with IH following the therapy with propranolol had a significantly increased (p = 0.022) circulating ECFC frequency, that showed a diminished tube-like formation capacity in vitro, and an altered constitutive store-operated Ca²⁺ entry. ECFCs play a role in IH pathogenesis; the response to propranolol therapy is associated with their increased frequency in the peripheral blood and a reduction of their vasculogenic activity. ^* These authors equally contributed to the manuscript.