Inflammatory Cytokines and Acute Graft-Versus-Host Disease (aGVHD) after Reduced Intensity Conditioning (RIC) Allogeneic Stem Cell Transplantation (allo-SCT).
Authors: Mohty Mohamad , Gaugler Beatrice , Faucher Catherine , Vey Norbert , Bouabdallah Reda , Stoppa Anne-Marie , Viret Frederic , Gravis Gwenaelle , Olive Daniel , Blaise Didier 
Published: April 2020

Abstract
Several lines of evidence have suggested that inflammatory cytokines act as mediators of aGVHD. Perturbation of the cytokine network may function as a final common pathway of target organ damage, and the rapid onset of severe aGVHD can be considered a “cytokine storm”. The use of RIC regimens has modified the natural history of transplant-related complications, especially aGVHD. Our current knowledge of the pathophysiology of aGVHD is based primarily on results of analyses performed in the myeloablative allo-SCT setting. The aim of this study was to investigate the role of inflammatory cytokines on aGVHD incidence and severity in 113 patients who received a RIC allo-SCT from an HLA-identical sibling. Plasma levels of 10 different cytokines (IL-1beta, IL-6, IL-8, IL-10, IL-12p70, IL-18, TNF-alpha, IFN-alpha, IFN-gamma, and Fas-ligand) were measured by ELISA prior to allo-SCT, at day 0 prior to graft infusion, and at regular times within the first 3 months after allo-SCT. Except for IL-12p70, all measured cytokines showed little variations in the blood in the first three months after allo-SCT. The incidence of grade II–IV aGVHD was 45% (95%CI, 36–54%; median onset, 32 days after allo-SCT). In the subgroup of patients for whom all tested cytokines could be measured closely, but rigorously prior to aGVHD clinical onset, a high IL-12p70 level (P&lt;10−4) measured around the first month after allo-SCT were significantly associated with the development of clinically significant grade II–IV aGVHD. IL-12p70 levels were significantly correlated to the severity of aGVHD: grade 0–I, median 468 pg/ml; grade II, median 2538 pg/ml; and grade III–IV, median 4615 pg/mL (P&lt;.0001). In patients experiencing grade II–IV aGVHD, IL-12p70 levels decreased after aGVHD therapy. Interestingly, we found a more rapid recovery of monocytes, that are the main pool of IL-12p70-secreting myeloid dendritic cells (DC), prior to aGVHD clinical onset in patients with grade II–IV aGVHD, as compared to patients with grade 0–I aGVHD (median, 829/μL vs. 552/μL; P=.005). At the effector level, we observed a significantly more robust recovery of genuine naïve CD3+CD4+CD45RA+CD27+ T cells prior to aGVHD clinical onset, in patients with grade II–IV aGVHD, as compared to patients with grade 0–I aGVHD (median, 50/μL vs. 16/μL; P=.006). Finally, in multivariate analysis, IL-12p70 level measured before aGVHD clinical onset was the strongest predictive factor for aGVHD development and severity (P&lt;10−4; RR=10.7; 95%CI, 3.8–30.6).
Overall, these findings reconstitute a genuine Th1 loop, supporting a model where aGVHD primarily reflects a type 1 alloreaction (rapid monocytes/DC recovery, IL-12p70 secretion, naïve CD4+ T cells expansion, Th1 and Tc1 cells differentiation) in the context of RIC allo-SCT. The fine functions of immune effectors would tend to be more evident in such less toxic regimens, offering new opportunities for a better understanding of aGVHD pathophysiology and therapy.