Combined positive/negative purging and transplantation of peripheral blood progenitor cell autografts in breast cancer patients: a pilot study

This trial studied the feasibility and efficiency of a novel procedure of double purging to eliminate tumor cells from leukapheresis products of stage IV breast cancer patients. After induction and mobilization therapy, 35 leukapheresis products from 16 breast cancer patients were subjected to CD34+ enrichment (i.e., positive selection) with the Isolex 300™ device and subsequent immunomagnetic depletion of tumor cells (i.e., negative selection) using a cocktail of three monoclonal antibodies directed against epithelial antigens. Patients with clinical response to induction chemotherapy proceeded to tandem high-dose chemotherapy, which consisted of melphalan (140 mg/m2) followed by retransfusion of the purged graft. After hematologic recovery, patients received ifosfamide 14 g/m2, carboplatin 1.5 g/m2, and etoposide 1.5g/m2 (ICE), again followed by autografting. After positive selection, a median purity of 96.6% CD34+ cells (range 48.4–99.2%) and a recovery of 56.8% (range 25.8–92.6%) were achieved. Subsequent negative purging resulted in a median CD34+ purity of 97.2%. Overall CD34+ recovery after both purging procedures was 51.1% (range 18.5–82.4%). Tumor cells were detectable in 8 of 16 (50%) starting fractions before purging. After both purging cycles, only 1 of 16 autografts remained positive for tumor cells compared to 3 of 16 after CD34+ selection. A calculated purging efficiency of 2 to >4 log was achieved. Engraftment was rapid, reaching ≥500/μL neutrophils on day +10 after melphalan and on day +9 after ICE. A platelet count of ≥20.000/μL was reached on day +12 after melphalan and on day +11 after ICE. Thus, combining positive and negative purging is feasible, further enhances purging efficiency, and does not compromise the quality of the graft, leading to rapid engraftment after high-dose chemotherapy.