Factors influencing white blood cell mobilisation in healthy granulocyte donors

Background: Granulocyte transfusions represent a therapeutic option for severely neutropenic patients with bacterial or fungal infections that are otherwise unresponsive to conventional therapy. Prior clinical studies suggest that patients receiving higher granulocyte doses achieve superior outcomes. Consequently, suboptimal donor stimulation and collection leading to lower granulocyte doses likely correlate with worse clinical outcomes.

Study design: A retrospective analysis was conducted on mobilisation data from 312 granulocyte collections from healthy donors between January 2020 and May 2023. This study was performed in a single blood donor center exclusively supporting a comprehensive cancer center. Donors underwent stimulation with 480 mcg of filgrastim (granulocyte colony stimulating factor [G-CSF]) subcutaneously and 8 mg of dexamethasone orally administered 12 to 14 h before collection. The correlation between donor characteristics (age, gender, body weight (BW), body mass index (BMI), baseline haemoglobin (Hgb), and platelet (PLT) counts) and mobilisation efficiency (Δ WBC, defined as post-mobilisation WBC count-baseline WBC count) was examined to identify factors associated with enhanced mobilisation efficiency. Additionally, the impact of multiple donations on Δ WBC in repeat donors was assessed.

Results: The median donor age was 43 years (range 18-81), with 224 male and 88 female donors. Female donors exhibited significantly higher baseline PLT counts and post-mobilisation WBC counts. However, donor gender did not significantly affect Δ WBC. A negative correlation was observed between Δ WBC and age (r = -0.235, p = 0.001), with older donors (61-81 years) exhibiting significantly lower mobilisation efficiency. BW and BMI differences had no significant effect on Δ WBC. A positive correlation was identified between baseline PLT count and Δ WBC (r = 0.140, p = 0.014), with females having significantly higher baseline PLT counts (p = 0.0004). No correlation was found between Δ WBC and baseline Hgb (r = 0.004, p = 0.477). Repeat donors showed no statistically significant change in Δ WBC with subsequent donations, with a mean interval of 136.5 days between collections.

Conclusion: Mobilisation efficiency was not impacted by donor BW or BMI suggesting that BW-based G-CSF stimulation is not essential for optimising WBC mobilisation. Rather, a fixed single dose of 480 mcg of G-CSF and 8 mg of dexamethasone was sufficient to mobilise donors, thus reducing the procedural costs and the potential risks for medication-related side effects. The positive correlation found between baseline PLT count and Δ WBC suggests that PLT count could be used as a potential predictor of mobilisation efficiency. Mobilisation response in up to four collections in repeat granulocytes donors was not affected in subsequent donations. However, sample size is a limitation, and more data is needed for a meaningful conclusion of whether frequent granulocyte donations are safe and effective.