Background. Chronic graft-versus-host disease (cGVHD) represents a double-edged sword. In its nonsevere form, cGVHD associates with better control of the malignant disease, thus highlighting graft-versus-leukemia effects. However, severe cGVHD leads to debilitating morbidity and increased nonrelapse mortality. The prediction of severe cGVHD, in particular at disease onset, is therefore of high importance for ensuing clinical decisions and overall success of allogeneic stem cell transplantations. CXC-chemokine ligand 9 (CXCL9) is an interferon-inducible chemokine of the CXC family and is increased in cGVHD. Endothelial activation and stress index (EASIX) was shown to predict death after acute graft-versus-host disease. We explored CXCL9 and EASIX as predictors of severe cGVHD. Methods. Sera and clinical data of 480 patients were available who survived at least 6 months following allogeneic stem cell transplantation without steroid-refractory acute graft-versus-host disease and without early relapse. CXCL9 and EASIX were measured on day +100 and onset of cGVHD. Results. Development of nonsevere cGVHD was significantly associated with improved overall survival (hazard ratio 0.53, P < 0.001). CXCL9 serum levels at the onset of cGVHD predicted the development of severe cGVHD later on (hazard ratio 1.33, P = 0.02). In contrast, EASIX at the onset of cGVHD was not associated with cGVHD severity but was a significant independent risk factor for overall mortality and nonrelapse mortality. Conclusions. CXCL9 levels at the onset of cGVHD can help to predict severe courses of the disease and have potential for optimizing tailored administration of immunosuppressive therapy.

Patients with cancer frequently receive immune-checkpoint inhibitors (ICIs), which may modulate immune responses to COVID-19 vaccines. Recently, cytokine release syndrome (CRS) was observed in a patient with cancer who received BTN162b2 vaccination under ICI treatment. Here, we analyzed adverse events and serum cytokines in patients with 23 different tumors undergoing (n = 64) or not undergoing (n = 26) COVID-19 vaccination under ICI therapy in a prospectively planned German single-center cohort study (n = 220). We did not observe clinically relevant CRS (≥grade 2) after vaccination (95% CI 0–5.6%; Common Terminology of Adverse Events v.5.0) in this small cohort. Within 4 weeks after vaccination, serious adverse events occurred in eight patients (12.5% 95% CI 5.6–23%), six patients were hospitalized and two patients died. Despite absence of CRS symptoms, a set of pairwise-correlated CRS-associated cytokines, including CXCL8 and interleukin-6 was >1.5-fold upregulated in 40% (95% CI 23.9–57.9%) of patients after vaccination. Hence, elevated cytokine levels are common and not sufficient to establish CRS diagnosis.

Highlights d High IDO activity and an activated Kyn pathway are common in all cGVHD subtypes d Specific Kyn metabolism patterns were identified for gastrointestinal and fibrosing cGVHD d A pathway shift toward anthranilic and kynurenic acid was found in fibrosing cGVHD d A rationale for vitamin B2/B6 adjustment for cGVHD prevention is presented

Background: Fibrosing chronic graft-versus-host disease (cGVHD) is a debilitating complication after allogeneic stem cell transplantation (allo-SCT), and its pathophysiology is poorly understood. Kynurenine and its metabolites were shown to associate with both, interferon-gamma (IFNg) activation and fibrosis. This study investigates the interplay between members of the IFNγ pathway and Kynurenin-derived metabolites in cGVHD. Methods: Using a liquid chromatography tandem mass spectrometry approach on sera obtained on day+100 (n=430) and/or at onset of cGVHD symptoms (n=196) of our prospectively collected biobank after alloSCT, we measured concentrations of Kyn pathway metabolites (kynurenin (Kyn), anthranilic acid (AA), kynurenic acid (KA), 3-hydroxykynurenine (3-HK), and 3-hydroxy-anthranilic acid (3-HAA). We also measured C-X-C chemokine ligand 9 (CXCL9), interleukin (IL-)18, tryptophane (Trp) and indoleamine-2,3-dioxygenase (IDO) by ELISA. Results: We observed increased CXCL9 and IDO levels, and increased activity of the Kynurenine pathway in both non-severe and severe cGVHD. Interestingly, severe fibrosing cGVHD differed from any other form of cGVHD in a significant pathway shift toward AA and KA. This resulted in a reduced 3-HAA/AA ratio. A score consisting of low 3-HAA/AA ratio and high KA serum levels at onset of mild cGVHD symptoms predicted risk specifically of severe fibrosing cGVHD. This altered pathway in severe fibrosing cGVHD correlated with reduced activity of the Vitamin-B2-dependent kynurenine monooxygenase, low vitamin B6, and increased interleukin-18. Our results are consistent with a triple-hit model for fibrosing cGVHD including low activity of kynurenine monooxygenase (KMO, Vitamin B2 and B6 dependent) in the context of high IL18 serum levels and CXCL9-induced IDO activation (Figure 1). Conclusion: Chronic GVHD associates with an IFNg signature and increased activity of the Kynurenin pathway. KA and 3-HAA/AA defined the first molecular distinction between fibrosing and non-fibrosing cGVHD. The mechanism may involve Vitamin B2/B6 deficiency, and high CXCL9 and IL18. The Kyn metabolite signature is a candidate biomarker for severe fibrosing cGHVD and provides a rationale for translational trials on prophylactic Vitamin B2/B6 supplementation for cGVHD prevention. Figure 1: Triple hit model of fibrosing cGVHD (Hypothesis): Severe fibrosing cGVHD associates with a strong CXCL9-induced activation of IDO. The result of this activation is influenced by a reduced activity of kynurenine monooxygenase (KMO), either due to genetic polymorphisms or lack of Vitamin B2, and further aggravated by lack of Vitamin B6. The resulting metabolic deviation increases AA concentrations and reduces the 3-HAA/AA ratio. Finally, high IL-18 associates with increased serum KA. These three hits result in a metabolic situation with high KA and a low ratio 3-HAA/AA that predicts risk of fibrosing cGVHD. Figure 1 Figure 1. Disclosures Mueller-Tidow: Janssen Cilag: Consultancy, Research Funding; Pfizer: Consultancy, Research Funding; Bioline: Consultancy, Research Funding.