Predictive factors for peripheral-blood progenitor-cell collections using a single large-volume leukapheresis after cyclophosphamide and granulocyte- macrophage colony-stimulating factor mobilization

Purpose: (1) To study the ability of mobilized peripheral-blood progenitor cells (PBPC) collected in a single large-volume leukapheresis performed on a predetermined date to accelerate engraftment after high-dose cyclophosphamide and thiotepa; (2) to establish the minimum dose of PBPC associated with early engraftment; and (3) to identify parameters predictive of collection of large numbers of PBPC. Patients and Methods: Twenty-three patients with breast cancer received cyclophosphamide (4 g/m²) and granulocyte-macrophage colony- stimulating factor ([GM-CSF] 5 μg/kg/d x 15 days) for PBPC mobilization. A single leukapheresis was performed 15 days after cyclophosphamide administration. Then, patients received high-dose cyclophosphamide and thiotepa followed by reinfusion of PBPC and 4-hydroperoxycyclophosphamide (4HC)-purged bone marrow. PBPC concentration was measured in serial peripheral-blood samples and in the leukapheresis product. Correlation analysis between PBPC dose and engraftment and between leukapheresis yield and patient characteristics was attempted. Results: A single leukapheresis processed a median 36 L (range, 24 to 46) blood and collected 5 x 10⁶ CD34⁺ cells/kg (< 0.3 to 24) and 6.2 x 10⁵ colony-forming units granulocyte- macrophage (CFU-GM)/kg (< 0.001 to 29). All sixteen patients (70%) reinfused with ≥ 2.9 x 10⁶ CD34⁺ cells/kg reached a level of greater than 1,000 leukocytes/μL by day 13 and greater than 50,000 platelets/μL by day 15. All of these patients had a percentage of peripheral-blood CD34⁺ cells ≥ 0.5%, and all but one, a level of greater than 100,000 platelets/μL, on the day of leukapheresis. The bone marrow CD34⁺ cell percentage at study entry predicted the number of CD34⁺ cells collected after PBPC mobilization (R² = .42, P = .002). All patients with ≥ 2.5% bone marrow CD34⁺ cells experienced early engraftment. Conclusion: Reinfusion of PBPC collected in a single leukapheresis accelerates engraftment in the majority of patients. Pretreatment bone marrow CD34⁺ cell content determines PBPC mobilization capacity and may help select hematopoietic rescue strategies.