Poor Graft Function (PGF) Following In Vivo T Cell–Depleted Allogeneic Stem Cell Transplantation: The Role of Delayed Immune Reconstitution

Poor graft function (PGF) is a severe early complication of allogeneic hematopoietic stem cell transplantation (HSCT), defined by persistent cytopenias despite full donor chimerism. Its characterization has been limited by heterogeneous diagnostic criteria, impairing reliable estimates of incidence, risk factors, and biological correlates. An internationally harmonized definition was introduced in 2024 which provided a standardized framework for clinical and biological investigations, facilitating comparisons across studies. To assess the incidence, risk factors, clinical outcomes, and immune reconstitution associated with PGF using the 2024 harmonized definition in a large adult HSCT cohort. We conducted a retrospective single-center study including 655 consecutive adult HSCT recipients between 2015 and 2025. PGF was defined according to 2024 harmonized criteria. The primary endpoint was cumulative incidence of PGF; secondary endpoints included overall survival (OS), nonrelapse mortality (NRM), cumulative incidence of relapse (CIR), and immune reconstitution. Risk factors were assessed using univariate and multivariate logistic regression. Time-to-event outcomes were analyzed using competing-risk models and Simon-Makuch methodology. Immune reconstitution (CD3⁺, CD4⁺, CD8⁺, CD16⁺, CD19⁺ subsets) was evaluated longitudinally using linear mixed-effects and time-point analyses. PGF occurred in 46 patients (12-month cumulative incidence 7%), with a median onset of 86 days post-HSCT. In multivariate analysis, myelofibrosis (OR: 7.25, P < .001), myelodysplastic syndromes (OR: 4.91, P = .002), major ABO incompatibility (OR: 2.32, P = .019), CD34⁺ cell dose