Fatal acute graft-versus-host disease in Sézary Syndrome treated with Mogamulizumab and hematopoietic cell transplantation

s´ezary syndrome (SS) is a rare and aggressive T-cell lymphoma with a poor prognosis in advanced stages. allogeneic hematopoietic cell transplantation (allo-HCT) offers a potential cure, but complications such as graftversus- host disease (GvHD) remain a clinical challenge. mogamulizumab, a humanized anti-CC chemokine receptor 4 (CCR4) antibody, is sometimes used as a bridge to transplantation, but its potential interactions with allo-HCT are unclear. this report describes the case of a 37-year-old man with advanced SS who received mogamulizumab therapy followed by allo-HCT from an HLA-identical sibling donor. the patient developed severe gastrointestinal acute GvHD, which was treated with steroids and infliximab. however, the condition rapidly progressed to severe intestinal symptoms and life-threatening haemorrhagic shock, ultimately resulting in the patient’s death. this case highlights a potential link between mogamulizumab and severe acute GvHD promoted by drug-induced suppression of regulatory T cells. further research is required to fully understand the interaction between mogamulizumab and allo-HCT and to determine whether it is an optimal approach as a bridge to transplant therapy. this paradigmatic case suggests the need of personalizing transplant strategies by selecting appropriate conditioning therapy and GvHD prophylaxis to minimize potential toxicity.