Negative immunomagnetic purging of peripheral blood stem cell harvests from breast carcinoma patients reduces tumor cell contamination while not affecting hematopoietic recovery

BACKGROUND Because tumor contamination of hematopoietic stem cell grafts may influence the outcome in breast carcinoma (BC) patients undergoing high dose chemotherapy (HDC), several ex vivo procedures for the purging of autologous harvests have been investigated. The authors studied the presence of epithelial tumor cells and the growth of hematopoietic progenitors in peripheral blood stem cell (PBSC) collections from patients with metastatic breast carcinoma before and after a purging procedure performed by a negative immunomagnetic BC cell separation. METHODS Eighteen patients entered the study. Tumor contamination was assessed by conventional immunocytochemistry (ICC) and by a liquid culture assay developed in the study laboratory. Committed and more primitive hematopoietic progenitors were quantitated before and after the negative selection. Ten patients received HDC with purged PBSC support. RESULTS Before purging, 4 of 18 PBSC collections were found to be contaminated by liquid culture; among these samples, only 1 was positive by ICC. Three of the four positive collections, including the ICC positive sample, became negative after immunomagnetic selection whereas BC cells still were present after the procedure in one harvest. A high recovery of both primitive and mature hematopoietic progenitors was found after the purging procedure. Patients receiving purged PBSC after myeloablation had a prompt and complete hematopoietic reconstitution, and no graft failure was observed at a median follow‐up of 1 year. CONCLUSIONS The preliminary results of the current study suggest that negative selection of BC cells is able to purge PBSC effectively while having no apparent affect on hematopoietic progenitor recovery in vitro and in vivo. Cancer 2000;88:2758–65. © 2000 American Cancer Society. The current study shows the feasibility of a large‐scale negative immunomagnetic purging of breast carcinoma cells contaminating peripheral blood stem cell harvests. To the authors' knowledge it also is the first study to document that stem cell collections undergoing ex vivo manipulations aimed at removing epithelial cells can be reinfused safely to myeloablated patients and allow a prompt hematopoietic reconstitution.