Terminal Complement Activation in Children with Sinusoidal Obstructive Syndrome after Hematopoietic Cell Transplantation

Background: Sinusoidal obstructive syndrome (SOS) is an early, life-threatening endothelial disorder of hematopoietic cell transplantation (HCT). Low L-ficolin (LF), a lectin complement pathway mediator, is a published predictive and prognostic SOS biomarker. We hypothesized that the terminal complement pathway may be activated in SOS as endothelial damage can result in inappropriate terminal complement activation, sC5b-9, a critical driver in a related endothelial disorder, transplant-associated thrombotic microangiopathy (TA-TMA). The objective was to determine if sC5b-9 is increased in children with SOS, validate the published predictive and prognostic biomarkers LF, ST2 and hyaluronic acid (HA), and determine the relationship between these 4 markers.

Methods: In this IRB approved study, SOS was diagnosed using eBMT criteria and severe disease defined by multi-organ dysfunction (MOD). Samples from day 0 and 7 in serially enrolled allogeneic HCT recipients from 08/19-09/23 were assayed for sC5b-9, LF, ST2, and HA using single ELISAs. Descriptive statistics were used to compare biomarkers on day 0 and 7 in SOS versus no SOS. Receiving operating characteristics (ROC) predicting the SOS were calculated for each biomarker. Linear correlation of each biomarker was tested using Pearsons’s correlation coefficients. GraphPad Prism v10 (Boston, MA) was used for analysis.

Results: One hundred three patients were in the study, with median age of 11.7 years (range 0.4- 51.7), 36 (34.6%) Black, 42 (44.2%) unrelated donor source, 75 (79.6%) receiving marrow. Twenty-six (25%) developed SOS a median of day 16.7 days post HCT (range 5 to 43). Defibrotide was used for prophylaxis (6,5.7%) and treatment in 17 (65.4%). Despite early treatment, 10 (38.5%) developed severe disease. Day 100 non-relapse related mortality was significantly higher in those with SOS versus no SOS (30.7% vs 8%. p= 0.006).

There were no significant differences of LF, HA, ST2, or sC5b-9 on day 0 in those who later developed SOS and those who did not. On day 7, LF was significantly lower (median 1639 ng/mL vs 8481 ng/mL, p= 0.004) and ST2 significantly higher (median 47.1 ng/mL vs 17.4 ng/mL, p= 0.03) in those with SOS versus those without. Day 7 LF values predicted the development of SOS with an AUC of 0.69 (95% CI 0.57-0.81), p=0.009. There were no significant differences in sC5b-9 on day 7 in the SOS vs no SOS (median 376.9 ng/mL vs 361.4 ng/mL, p=0.67), though there was a trend for higher day 7 HA values in those with SOS (median 9013 ng/mL vs 6081 ng/mL, p=0.06).

Children who later developed severe SOS (n=10) had significantly higher day 0 ST2 (median 35.8 vs 18.8, p=0.01) and HA (median 1143.0 vs 389.3, p=0.04) versus those without (n=16). Day 0 ST2 and HA AUCs for predicting severe SOS were 0.788 (95% CI 0.602-0.974), p=0.015 and 0.779 (95% CI 0.565 – 0.993), p=0.015, respectively. sC5b-9 levels were significantly lower in those with severe disease (median 114.9 ng/mL vs 251.8 ng/mL) with no difference in day 0 LF. No day 7 biomarkers were significantly different nor prognostic for severe SOS versus those without. Linear associations of biomarkers on day 7 were tested- LF was inversely correlated to ST2 (-0.61) and sC5b-9 was inversely correlated to HA (-0.69). There were no other significant linear relationships. No biomarkers predicted TA-TMA nor grade 2-4 acute GVHD on day 0 or 7.

Discussion: In a large pediatric cohort, we validated that low LF predicts SOS and elevated ST2 and HA are early prognostic biomarkers while early sC5b-9 elevation was not predictive of SOS development. Contrary to our hypothesis, severe SOS was linked to significantly lower sC5b-9 levels, which may be due to impaired hepatic production of LF and complement proteins from liver damage or excessive urinary loss from kidney damage. The inverse linear association of these markers and endothelial (ST2) and liver damage (HA) support this hypothesis. Additional studies are needed to validate these findings.