PBSC mobilization, collection and positive selection in patients with chronic lymphocytic leukemia

We report the results of PBSC mobilization and immune selection in 17 patients with advanced chronic lymphocytic leukemia (CLL) enrolled in a multicenter Italian study of autologous transplantation with peripheral CD34+ selected cells. Mobilization was achieved by cyclophosphamide (CY) 4 g/m2 + G-CSF 5 microg/kg. CD34+ cells were positively selected by means of avidin-biotin immunoaffinity columns (Ceprate SC) or immunomagnetic beads (Isolex 300i) systems. Evaluation of minimal residual disease was performed by PCR analysis of the IgH gene rearrangment on the apheresis product before and after selection. Our results showed that after CY a median of 3.6 x 10(6)/kg (0.5-12.8) CD34+ cells were collected with a median of two aphereses in 14 out of 17 patients; three failed to mobilize a number of CD34+ cells adequate for subsequent manipulation. We found that in CR patients CD34+ cell yield per apheresis was significantly higher than in PR patients (P < 0.05). Sixteen selection procedures were performed in 13 patients. CD34+ cell recovery was 33.5% (10-85) with a median final yield of 1 x 10(6)/kg CD34+. Two patients underwent marrow collection due to the low number of CD34+ cells recovered. Final purity was 59% (range 22-94) and CD5/20+ cell depletion was 2.7 log (1.6-4.4). Our data showed a statistically higher CD34+ cell recovery and purity with the Isolex device compared to Ceprate (P < 0.01 and 0.01, respectively). All the evaluable samples remained PCR positive after selection. The main issues to be addressed in the future are the identification of patients who fail mobilization and the improvement of purging methods.