Efficacy and safety of simultaneous immunomagnetic CD34+ cell selection and breast cancer cell purging in peripheral blood progenitor cell samples used for hematopoietic rescue after high-dose therapy.

We have established a new simultaneous positive/negative selection procedure using the Baxter Isolex 300i system. We tested its tumor cell (TC) purging efficacy by tumor contamination tests ex vivo and its safety in a group of 17 breast cancer (BC) patients by measuring hematopoietic recovery after high-dose (HD) therapy and autologous stem cell rescue with the selected cells. Tumor contamination tests resulted in a TC depletion of 4.1-6.0 log steps. The CD34+ cell yield in this experimental setting was 38.9-91.5%, and the CD34+ cell purity was 86.0-96.0%. In a group of 17 BC patients (5 high-risk adjuvant, > or = 10 lymph nodes positive, and 12 metastatic), we processed leukapheresis products (LPs) by simultaneous positive/negative selection. In these clinical samples, the mean CD34+ cell yield was 56.2% (range, 14.0-80.1%), and the CD34+ cell purity was 94.5% (range, 69.0-99.8%). Additionally, we screened samples of the patients' LPs before and after the purging procedure for contaminating TC by immunocytochemistry. In 15 of 17 tested cases, TCs were detectable prior to the purging procedure. After the procedure, we could not detect residual TCs in 16 of 17 cases. In one case, we found a highly reduced number of TCs. Furthermore, we evaluated the times for hematopoietic reconstitution in a group of five BC patients in the high-risk adjuvant situation who underwent HD chemotherapy and hematopoietic rescue with positive/negative selected stem cells and compared it with our own data from 10 BC patients who, after identical HD therapy, received only positively selected CD34+ cells and 14 patients who, after identical HD therapy, received autografts purged by incubation with toxic ether lipids (ET-18-OCH3). In all groups, a leukocyte count of >2000 cells/microl was reached at day +10. A platelet count of > 50,000 cells/microl was reached at day +12 in the ET-18-OCH3 group and at day +14 in the other two groups. Furthermore, 12 patients with metastatic disease rescued with positive/negative selected stem cells after HD therapy also showed fast and comparable hematopoietic recovery. The new simultaneous immunomagnetic positive/negative selection using a closed system is effective and safe. Processing LPs leads to a similar CD34+ cell yield, a higher TC depletion compared to standard CD34+ cell selection, and no delay in hematopoietic recovery.