Clinical impact of infused CD3-positive cell dose in unrelated peripheral blood stem cell transplantation.

The clinical impact of the infused CD3-positive cell dose on outcomes after unrelated peripheral blood stem cell transplantation (uPBSCT) remains uncertain, particularly regarding graft-versus-host disease (GVHD). We retrospectively analyzed 75 patients who underwent first uPBSCT between 2016 and 2024, dichotomized at the median infused CD3-positive cell dose (20 × 10⁷ cells/kg). The cumulative incidence of grade II-IV acute GVHD was significantly higher in the high CD3 group (45.7% vs 20.0% at day-100, p = 0.02). In multivariable analysis, high CD3-positive cell dose independently predicted acute GVHD (HR 3.15, 95% confidence interval 1.26-7.86) but was not associated with overall survival, non-relapse mortality, relapse, or chronic GVHD. Target-organ involvement and severity were similar between groups, although grade II acute GVHD was more frequent in the high CD3 group. In an exploratory analysis of patients receiving systemic corticosteroids for grade II-IV acute GVHD, progression of acute GVHD after first-line treatment occurred only in the high CD3 group, though based on small numbers and not statistically significant (p = 0.09). No GVHD-related mortality occurred. A higher infused CD3-positive cell dose increases acute GVHD risk without affecting other transplant outcomes and may serve as a practical marker of acute alloreactivity to guide risk-adapted GVHD prophylaxis.