Adhesion molecules on CD34⁺ cells were implicated in the process of peripheral blood stem cell (PBSC) mobilization and homing. We studied the mobilization of CD34⁺Thy1⁺ cells, CD34⁺ very late-acting antigen (VLA)4⁺ cells, and CD34⁺L-selectin⁺ cells in non-Hodgkin's lymphoma patients mobilized with cyclophosphamide plus G-CSF, GM-CSF, or GM-CSF followed by G-CSF. The mean percentage of CD34⁺ cells in the bone marrow (BM) expressing Thy1 was 23.6% ± 11% and 17.8% ± 8% in the PB before mobilization, and was markedly decreased to 4.5% ± 3.3% in the apheresis collections. Similarly, the mean percentage of CD34⁺ cells expressing L-selectin was 35.8% ± 4.3% in the BM, 21.6% ± 4.1% in the PB before mobilization and was markedly decreased to 9.1% ± 2.5% in the apheresis collections. Patients in the three arms of the study had a similar pattern of CD34⁺Thy1⁺ and CD34⁺L-selectin⁺ cell mobilization. Also, a similar pattern of coexpression of CD34⁺Thy1⁺ and CD34⁺L-selectin⁺ cells was observed when the patients were regrouped as “good mobilizers” (≥2 × 10⁶ CD34⁺CD45^dim cells/kg, in four collections) and “poor mobilizers” (<0.4 × 10⁶ CD34⁺CD45^dim cells/kg, in two collections).

The mean percentage of CD34⁺ cells expressing VLA-4 in the BM and PB was relatively high (73.4% ± 12% and 65.4% ± 6.6%, respectively) and dropped considerably in the PBSC collections to 43.5% ± 7.1% with a similar pattern observed for patients in arms A, B, and C. However, when the patients were regrouped as “good mobilizers” and “poor mobilizers,” a higher percentage of CD34⁺ cells expressing VLA-4 was observed in the PBSC of the pooled “good mobilizers” (50.5% ± 9% versus 36.3% ± 6.4%; p = 0.01). We conclude that release of CD34⁺ cells to the PB involves a general downregulation of Thy1, L-selectin and VLA-4 on CD34⁺ cells, irrespective of the growth factor used for mobilization. However, good mobilizers had a relatively higher percentage of CD34⁺ cells expressing the VLA-4 antigen.