Pre-Engraftment Syndrome After Autologous Stem Cell Transplantation in Relapsed or Refractory Hodgkin Lymphoma: An Association with Prior PD-1 Inhibitor Exposure

Background and Objectives: Autologous stem cell transplantation (ASCT) remains the standard of care for relapsed or refractory Hodgkin lymphoma (R/R HL), and an increasing proportion of patients receive programmed cell death protein 1 (PD-1) inhibitors prior to transplantation. Engraftment syndrome (ES) is a noninfectious inflammatory complication classically associated with neutrophil recovery; however, early peri-transplant inflammatory manifestations remain poorly characterized and may mimic infectious complications. We aimed to evaluate peri-transplant inflammatory events after ASCT, with particular emphasis on ES-compatible manifestations occurring before neutrophil engraftment and their association with prior PD-1 inhibitor exposure. Materials and Methods: In this single-center retrospective cohort study, 64 consecutive adult patients with HL undergoing ASCT between 2018 and 2025 were analyzed. ES was defined according to Spitzer and Maiolino criteria. Inflammatory manifestations fulfilling these criteria but occurring prior to neutrophil recovery were classified as pre-engraftment syndrome (pre-ES). Clinically significant events were defined by the requirement for systemic corticosteroid therapy. Clinical and laboratory parameters were compared using non-parametric statistical analyses. Results: No cases fulfilled the Spitzer criteria for classical ES, while three patients (4.7%) met the Maiolino criteria, none requiring corticosteroid therapy. Using the broader Maiolino definition, pre-ES was observed in 34 patients (53.1%) when the conventional engraftment time window was disregarded; however, only three patients required systemic corticosteroid therapy. Importantly, all three cases also fulfilled the Spitzer criteria outside the conventional time window, whereas the remaining Maiolino-defined pre-ES cases were self-limiting. All steroid-requiring pre-ES cases occurred exclusively in PD-1-exposed patients, and prior PD-1 therapy was significantly associated with severe pre-ES (p = 0.0007), although this finding is based on a very small number of events. These patients also demonstrated significantly higher early C-reactive protein (CRP) levels. Conclusions: While classical ES after ASCT was uncommon, clinically significant pre-ES occurred exclusively in PD-1-exposed patients. These early inflammatory events may represent a distinct phenotype and require prompt recognition and timely corticosteroid therapy after exclusion of infection. Prospective studies are warranted to validate these findings and refine risk stratification and monitoring strategies.