Association of initial interface formation time with CD34+ collection efficiency in continuous mononuclear cell collection: A retrospective study

Background: Factors influencing CD34+ cell collection efficiency (CE) during peripheral blood stem cell harvesting have been investigated; however, the impact of procedural management remains unclear. In continuous mononuclear cell (CMNC) collection, a stable cell–plasma interface (IF) is formed through channel priming, initial IF establishment, and mononuclear cell (MNC) collection. Although IF instability is known to impair CE, the adequacy of initial IF formation has not been examined as an independent factor. Therefore, we focused on the time required for initial IF formation and its association with CE.
Methods: We retrospectively analyzed 291 Spectra Optia CMNC procedures (52 autologous and 239 allogeneic) performed between 2016 and 2025. Initial interface formation time (IFT) was defined as the interval from the start of the procedure to transition to MNC collection. CE2 was defined as the ratio of collected CD34+ cells to the product of pre-apheresis peripheral blood CD34+ cell concentration and processed blood volume. Results: CE2 was lower in autologous than in allogeneic collections (41.3% vs. 59.2%) and was associated with longer IFT (median, 18 vs. 15 min). CE2 correlated with white blood cell count (r = −0.24), hematocrit (r = 0.36), and IFT (r = −0.23; all p < 0.001). In multivariable analysis, these factors remained independently associated with CE2, and IFT was inversely correlated with hematocrit (r = −0.44, p < 0.001).
Conclusion: IFT is independently associated with CE2 and provides insight into the early dynamics of IF formation during leukapheresis, highlighting an underexplored procedural aspect of CE.