Elevation of White Blood Cell Count After G-CSF-Combined Conditioning Predicts Relapse and Disease-Free Survival Following Single-Unit Cord Blood Transplantation for Myeloid Malignancies.

[BACKGROUND] Granulocyte colony-stimulating factor (G-CSF) enhances the cytotoxicity of cytarabine (Ara-C) against myeloid leukemia cells, and G-CSF-combined conditioning regimens have been adopted in single-unit cord blood transplantation (CBT) at our institution. However, it remains unclear whether the degree of white blood cell (WBC) elevation during G-CSF administration predicts transplant outcomes.

[METHODS] We retrospectively analyzed 175 adult patients with myeloid malignancies who underwent first single-unit CBT with myeloablative conditioning (total body irradiation 12 Gy, high-dose Ara-C with G-CSF, and cyclophosphamide) at our institution between 2000 and 2024. The G-CSF priming effect was evaluated by the ratio and absolute difference in WBC counts before and after G-CSF administration. Patients were stratified into higher and lower groups based on receiver operating characteristic curve-derived cutoffs (WBC ratio ≥2.0, WBC difference ≥4.0 × 10⁹/L).

[RESULTS] Disease-free survival (DFS) was significantly higher in patients with a higher WBC ratio (71.5% versus 53.6% at 5 years, P = .001) and higher WBC difference (75.9% versus 57.9% at 5 years, P = .0009). In multivariate analysis, a higher WBC ratio was independently associated with improved DFS (HR, 0.58, 95% CI, 0.36 to 0.96, P = .035) and reduced relapse (HR, 0.46, 95% CI, 0.23 to 0.92, P = .028). A higher WBC difference was also associated with reduced relapse (HR, 0.44, 95% CI, 0.19 to 0.99, P = .049). Neither WBC parameter was associated with non-relapse mortality or engraftment. Notably, the beneficial effects of higher WBC ratio and difference were confined to patients with high or very high risk of the refined Disease Risk Index.

[CONCLUSIONS] Elevation of WBC counts during G-CSF-combined conditioning predicts favorable outcomes after single-unit CBT, particularly in patients with high-risk myeloid malignancies.