BACKGROUND: Hematopoietic stem cell transplantation (HSCT) success relies on timely engraftment and immune reconstitution. While neutrophil and platelet recovery are well-established clinical endpoints, the dynamics of monocyte engraftment and their relationship with hematopoietic recovery remain insufficiently characterized. METHODS: In this prospective observational study, 56 patients undergoing autologous (n = 32) or allogeneic (n = 24) peripheral blood stem cell transplantation were enrolled. Pre-engraftment monocyte peak day was defined based on serial complete blood counts. Flow cytometric analysis was performed at the time of monocyte engraftment to assess monocyte (CD14/CD16) and lymphocyte subsets. Associations between monocyte dynamics and neutrophil and platelet engraftment were evaluated using correlation and multivariable regression analyses. RESULTS: Allogeneic recipients demonstrated significantly delayed neutrophil engraftment compared to autologous patients (p=0.003). Pre-engraftment monocyte peak day was strongly correlated with neutrophil engraftment (ρ = 0.83, p < 0.001) and moderately correlated with platelet engraftment (ρ = 0.46, p = 0.001). In multivariable analyses, monocyte peak timing remained independently associated with both neutrophil (B = 0.87, p < 0.001) and platelet recovery (B = 1.53, p = 0.015), whereas CD34⁺ cell dose showed no independent association. Flow cytometric analysis demonstrated predominance of CD14⁺ monocytes during early engraftment. Despite elevated inflammatory markers in patients with complications, engraftment kinetics remained comparable. CONCLUSIONS: Pre-engraftment monocyte dynamics are strongly associated with subsequent hematopoietic recovery and may serve as an early indicator of engraftment following HSCT. These findings support the potential utility of monocyte-based monitoring in post-transplant care and highlight the need for further studies to validate their prognostic value.
Melik et al. (2026) studied this question.