Allogeneic stem cell transplantation (allo-SCT) remains the only potentially curative treatment for myelofibrosis (MF). 1, 2 The 5-year overall survival (OS) rates in MF patients after allo-SCT have improved over the past several years, ranging from 47% to 62%. 3-7 However, relapse after transplantation remains a frequent cause of death, with relapse rates ranging from 10-43% after allo-SCT. 1, 8 Strategies for detecting early relapse and improving outcomes in these high-risk patients represent an unmet need.

Assessing response and confirming early relapse after transplant for MF is often challenging based on the clinical criteria, 9 and it usually takes a few months for fibrosis to resolve and the bone marrow morphologic remission to be achieved. 10 Detecting the JAK2 V617F mutation after SCT in MF is a strong predictor of relapse and a potential marker for guiding adoptive immunotherapy. 7, 11-13 Few studies have focused on the potential role of mixed chimerism in predicting early relapse, particularly in those with mixed myeloid chimerism (MMC). 14-18 The influence of MMC on posttransplantation relapse of MF has not been well studied. Therefore, we aimed to determine the role of MMC in predicting relapse in MF patients after allo-SCT. We further explored the correlation between myeloid chimerism and molecular relapse of MF.