Single Nucleotide Polymorphisms Within The Thrombomodulin Gene (THBD) Predict Risk Of Non-Relapse Mortality In Patients With Graft-Versus-Host Disease
Authors: Luft Thomas , Penack Olaf , Blau Olga , Dietrich Sascha , Isermann Berend H. , Ho Anthony D , Uharek Lutz , Dreger Peter , Kumar Rajive , Rachakonda Krishna P.S. 
Published: October 2019

Purpose
Acute graft-versus-host disease (GVHD) is a major complication after allogeneic stem cell transplantation (allo-SCT). With the current treatment approaches focussing on escalating immunosuppression, mortality rates of therapy-refractory disease courses are approx. 80-90%, underlining the medical need for novel therapeutic concepts. The pathophysiology of refractory GVHD is incompletely understood, however, recent evidence points towards a crucial role for endothelial damage. We have previously shown that steroid-refractory GVHD associates with increasing serum thrombomodulin (TM) levels 1, 2 and loss of endothelial TM expression 3, a constellation that indicates endothelial stress. However prior to allo-SCT, baseline TM levels did not predict steroid-refractory GVHD or survival. We hypothesized that endothelial vulnerability caused by single nucleotide polymorphisms within the TM gene (THBD) is a risk factor for refractory GVHD predicting outcome after allo-SCT.

Patients and Methods
Seven SNPs within the THBD gene were studied (rs1962.TC, rs1042579.TC, rs1042580.AG, rs3176123.TG, rs3176124GA, rs3176126.GA and rs3176134.CT) in a training cohort of 465 allografted patients. The relevant genotypes were then re-assessed in an independent validation cohort (n=386).

Results
Allele frequencies of seven THBD SNPs allowed meaningful statistical correlation with outcome after allo-SCT. An increased risk of non-relapse mortality (NRM) was associated with three SNPs: rs1962.CC, rs1042579.TT (455V) and rs1042580.GG. When patients were divided into risk cohorts (one vs. no high-risk SNP), a strong correlation with NRM was observed in both cohorts (training cohort: p=0.002, HR 2.32 CI 1.36-3.95; validation cohort: p=0.007, HR 2.13, CI 1.23-3.70) (Figure 1). NRM was predicted by THBD SNPs in particular for patients who later develop GVHD (validation cohort: p=0.00056, HR 3.03 CI 5.68-1.61, training cohort: p=0.012, HR 2.38 CI 1.21-4.69) but not in patients without GVHD. In contrast, THBD SNPs did not predict incidence of acute GVHD. Multivariate analyses adjusting for clinical variables confirmed the independent effect of THBD SNPs on NRM in both cohorts.

Conclusions
Our results demonstrate that THBD-SNPs predict mortality of GVHD patients without influencing GVHD incidence. This supports our hypothesis that endothelial vulnerability contributes to therapy refractory courses of the disease. Rather than focussing on the escalation of combinations of (endothelial cell toxic) immunosuppressive drugs, therapeutic approaches aiming at endothelial protection should be evaluated.
1. Dietrich S, Falk CS, Benner A, et al. Endothelial vulnerability and endothelial damage are associated with risk of graft-versus-host disease and response to steroid treatment. Biol Blood Marrow Transplant 2013; 19(1): 22-7.
2. Luft T, Dietrich S, Falk C, et al. Steroid-refractory GVHD: T-cell attack within a vulnerable endothelial system. Blood 2011; 118(6): 1685-92.
3. Andrulis M, Dietrich S, Longerich T, et al. Loss of endothelial thrombomodulin predicts response to steroid therapy and survival in acute intestinal graft-versus-host disease. Haematologica 2012; 97(11): 1674-7.

Disclosures:
Dreger: Riemser Pharma : Consultancy, Honoraria, Research Funding.