Atypical serum protein electrophoresis (SPE) profiles may arise in patients who received allogeneic hematopoietic stem cell transplantation (allo-HSCT), but little is known about their clinical significance. Atypical SPE combine either monoclonal and oligoclonal components, suspected on SPE and confirmed by immunofixation. The aim of the study is to analyze the incidence, the etiology and the clinical significance of atypical SPE profiles in patients who received allo-HSCT.

This retrospective study enrolled 117 patients with myeloid malignancies who received an allo-HSCT between 2012 and 2018. We excluded patients with lymphoid malignancies or multiple myeloma, patients presenting atypical electrophoresis prior to transplantation and patients who died within 100 days post-transplant.

Atypical SPE occurred in 42.7% of patients. The cumulative incidence of atypical profiles was significantly higher in patients with acute Graft Versus Host Disease (GVHD, p = 0.019) and in patients with Cytomegalovirus (CMV) reactivation (p = 0.0017). We observed for the first time that atypical SPE profiles mostly occurred in patients transplanted from a CMV+ donor (p = 0.031). CMV reactivation preceded the occurrence of atypical SPE in the majority of patients. We show that atypical SPE delay the relapse of the underlying malignant disease (486 vs 189 days, p = 0.006), and significantly improve overall survival (OS; 33.1 months vs 28.3 months, p = 0.049). In both univariate and multivariate analyzes, the presence of an atypical SPE is the only factor that significantly improves OS.

The occurrence of atypical SPE profiles after allo-HSCT may reflect an adapted post-transplant immune response leading to favourable outcomes.