Differential Mobilization of CD34 + Cells and Lymphoma Cells in Non-Hodgkin's Lymphoma Patients Mobilized with Different Growth Factors

Abstract

Co-mobilization of CD34⁺ cells and tumor has been documented in patients with different types of cancer undergoing peripheral blood stem cell transplantation (PBSCT). Conflicting reports were published regarding the role of various growth factors in tumor cells mobilization, hence we studied the extent of CD34⁺ cells and lymphoma cell mobilization in 35 non-Hodgkin's (NHL) patients primed by cyclophosphamide (Cy) in combination with granulocyte colony-stimulating factor (GCSF) (A, 13 patients), granulocyte-macrophage (GM)-CSF (B, 10 patients), or GM-CSF followed by G-CSF (C, 12 patients). CD34⁺ cells were quantitated by flow cytometry and lymphoma cells by the TaqMan Real Time PCR for bcl-2 gene rearrangement. Successful collection in 4 days of ≥2× 10⁶ CD34⁺ cells/kg needed for prompt engraftment was obtained in 76%, 60%, and 58% of patients in arms A, B, and C, respectively. Lymphoma cell mobilization was detected in 35% patients tested, 78% of which had follicular lymphoma. Lymphoma cell mobilization was similar in the three arms of the study, however, presence of lymphoma cells was prevalent in patients who failed to mobilize the amount of 0.4 × 10⁶ CD34⁺ cells/kg in 2 days ("poor mobilizers") and reached 42%, compared to 17% in the "successful mobilizers" group of patients. Lymphoma cell contamination in PBSCs was detected proportionately in the peripheral blood and in the bone marrow. We conclude that bcl-2 gene rearrangement is prevalent in patients with follicular histology, and, in these patients, an inverse relationship was observed between mobilization of CD34⁺ cells and lymphoma cells. Our results explain the high relative risk (1.98) for mobilization in patients with follicular histology.