Supplementary Material for: Multiplex proteomics in the identification of potential biomarkers of very severe sinusoidal obstruction syndrome/veno-occlusive disease (SOS/VOD) in allogeneic hematopoietic cell transplant patients treated with defibrotide

Introduction
Despite well-established clinical criteria for diagnosis of SOS/VOD following allogeneic HCT, there is a lack of established diagnostic protein biomarkers.

Methods
Prospective samples were collected from patients with very severe SOS/VOD at diagnosis and days +3, +7, +14, and +30 post-initiation of defibrotide. Samples from age-matched controls with no VOD were collected at day +14, +30, +60, +90 and +180 following allogeneic HCT. Serum samples were analyzed for 2925 protein levels by antibody-based proximity extension assay (PEA). Mean differences in the log-transformed abundance values were compared using t-tests in a volcano plot.

Results
Five patients with very severe SOS/VOD and five control patients were compared. Ten proteins were identified that showed a statistically significant and log-transformed 3-fold increase in concentration. They were CALCA, CCL20, GPR37, IGFBP4, IL1RL1, SLC39A14, SPINK4, FABP3, MYL3, and CHCHD10. Four different proteins, namely CD83, LAIR2, CD7, and HEM6 showed a significant decrease with defibrotide treatment. SOS/VOD resolved in 80% (n=4) of patients, while one patient deceased due to SOS/VOD.

Conclusion
PEA technology identified 10 proteins that were significantly elevated in patients with very severe SOS/VOD. Prospective studies in a larger cohort using this technology may be able to conclusively identify diagnostic protein biomarkers for SOS/VOD.