Evaluation of Circulating Endothelial Cells as Direct Marker of Endothelial Damage in Allo-Transplant Recipients at High Risk of Hepatic Veno-Occlusive Disease/Sinusoidal Obstruction Syndrome

Sinusoidal obstruction syndrome (SOS), also known as veno-occlusive disease (VOD), is a rare but potentially fatal complication following allogenic hematopoietic cell transplantation (allo-HCT). Timely identification of SOS/VOD for prompt treatment is critical, but identifying a VOD predictive biomarker is still challenging. Given the pivotal role of endothelial dysfunction in SOS/VOD pathophysiology, the CECinVOD study prospectively evaluated Circulating Endothelial Cells (CEC) levels in patients undergoing allo-HCT with myeloablative conditioning regimens (MAC) to investigate their potential in predicting and diagnosing SOS/VOD. 150 patients were enrolled from 11 Italian Bone Marrow Transplantation Units. All participants, aged over 18 years, received myeloablative conditioning regimens, placing them at higher risk of developing SOS/VOD. Overall, six cases of SOS/VOD (4%) were recorded. CECs were detected using the FDA-approved CellSearch system, an immunomagnetic selection based platform incorporating ferrofluid nanoparticles and fluorescent-labelled antibodies. They were defined as CD146+, CD105+, DAPI+ and CD45-. Blood samples were collected at the following timepoints: before (T0) and at the end of conditioning treatment (T1), at neutrophil engraftment (T2), and 7-10 days post-engraftment (T3). For patients who developed VOD, additional samples were collected at any suspected or proven VOD onset (T4) and weekly during defibrotide treatment (T5-T8). Baseline CEC count exceeding 17 per ml was associated with a higher SOS/VOD occurrence (p 0.04), along with bilirubin levels exceeding 1.5 mg/ml and a haploidentical donor hematopoietic stem cell source. Post-conditioning regimen (T1) CEC levels were elevated (p 0.02), and they further increased at engraftment (p<0.0001). Additionally, patients developing SOS/VOD post-engraftment showed a marked higher relative increase in CEC counts than those who did not (p 0.04), particularly among patients experiencing late-onset SOS/VOD (relative increase exceeding 150%). Multivariate analysis supported these findings, along with a high Endothelial Activation and Stress Index (Easix) score at engraftment (T2). Finally, CEC kinetics corresponded with defibrotide treatment. After therapy start (T4), CEC levels showed an initial increase in the first week (T5), followed by progressive decrease during VOD treatment (T6 and T7) and returning to pre-SOS/VOD onset levels at resolution of the complication. In conclusion, this prospective multicenter study revealed a low incidence of SOS/VOD in high-risk patients compared to historical data, but in line with recent reports. The results from the CECinVOD study collectively confirm the endothelial injury in allo-HCT and in SOS/VOD development, suggesting CECs as a valuable biomarker for its diagnosis and for the identification of patients at higher risk of this complication, especially in cases of late-onset SOS/VOD. Furthermore, CEC kinetics may assist in treatment strategies by providing insights into the optimal timing for discontinuing defibrotide treatment.