Circulating Endothelial Cells As a Marker of Vascular Injury in Pediatric Patients

Introduction Thrombotic microangiopathy (TMA), hepatic veno-occlusive disease (VOD) and GVHD are major causes of morbidity and mortality in hematopoietic stem cell transplant (HSCT) recipients. Current strategies to identify these complications involve surveilling markers of immune activation and organ function. Unfortunately, these processes are frequently identified after organ damage has occurred, creating the need for a timelier marker of disease. Circulating endothelial cells (CECs) have been shown to directly reflect vascular injury and are a potential tool for identifying early evidence of endothelial damage. Our study quantifies and characterize CECs in pediatric patients undergoing HSCT and aims to identify the timing of peak vascular injury relative to transplant as well as the relationship between CECs and post-transplant vascular complications. Methods CEC analysis was performed prior to and after stem cell infusion. All patients had central venous catheters. CEC identification was done on whole blood using Invitrogen M-450 Tosylactivated Dynabeads coupled to a CD146 antibody. Confirmatory staining after immunomagnetic isolation was done using acridine orange and propidium iodide (AOPI). CEC identification criteria are shown in Figure 1. Two reviewers quantified CECs by morphology and bead number. Negative controls were done using healthy donor blood. Results CEC testing was done on 8 HSCT patients (Fanconi Anemia=1, AML=2, ALL=2, ICF-1 syndrome=1, Hemoglobin Hammersmith=1 and macrophage activation syndrome =1). 6 conditioning regimens were myeloablative and 2 were reduced intensity. CEC quantification for individual patients is shown in Figure 2. The vast majority of patients (n=7) had a peak CEC value prior to day 14, including 4 patients whose peak value occurred prior to stem cell infusion. Clinical complications are described in Figure 2. The two highest CEC values recorded were in patients with severe complications, including cardiac arrest (Patient 5, 124 CECs/mL) and death (Patient 7, 84 CECs/mL). The individual difference between lowest recorded CEC value and peak CEC value was also greatest in these patients (Patient 5, 120 CECs/mL; Patient 7, 80 CECs/mL). Mean CEC values for HSCT patients and controls are shown in Figure 3. Conclusion CECs reliably peaked within the first 2 weeks of HSCT suggesting marked vascular injury occurs in this timeframe. CEC count peaked prior to stem cell infusion in half of these patients, which implies a large component of vascular injury is driven by the conditioning process. As predicted, the highest CEC values recorded were in patients with grave complications, including one patient who died from multiorgan system failure. Continued data collection will be informative as to whether the nature of these peaks or characteristics of the CECs themselves will predict future vascular complications.