Purging of peripheral blood stem cells yields BCR-ABL-negative autografts in patients with BCR-ABL-positive acute lymphoblastic leukemia.

Remission marrow from patients with BCR-ABL+ acute lymphoblastic leukemia (ALL) achieving clinical remission (CR) after induction or consolidation chemotherapy according to the German multicenter adult ALL (GMALL) protocol showed high titers of residual BCR-ABL+ cells. Therefore, we initiated a pilot study to monitor circulating BCR-ABL+ cells and to collect, purge, and autograft peripheral blood stem cells (PBSC) in these patients. After GMALL 05/93 high-risk phase II of induction chemotherapy (high-dose AraC 3 g/m2 x 8 does and mitoxantrone 10 mg/m2 x 3 doses), patients received 5-10 micrograms/kg subcutaneous recombinant human granulocyte colony-stimulating factor (rhG-CSF) daily. Mobilized CD34+ cells peaked between 20 and 26 days after starting chemotherapy at 4.8-75.6 (median 10.8) x 10(4)/mL peripheral blood (PB) (n = 5). Patients treated with additional chemotherapy cycles failed to mobilize adequate numbers of CD34+ cells. PB stem cells (PBSC) were purged using a cocktail of CD10, CD19, and AB4 monoclonal antibodies (mAbs) coupled to immunomagnetic beads (IMB). The median recoveries of total nucleated cells (TNC) and CD34+ cells after mAb/IMB purging were 84 and 81%. The peak numbers of CD34+ cells collected in a single leukapheresis were median 8.6 x 10(6)/kg pre- and 5.2 x 10(6)/kg postpurge (n = 4). The absolute prepurge CD19+ cells were as low as median 2.7 (range 1.4-19) x 10(6) per leukapheresis. Residual BCR-ABL+ cells in unpurged leukapheresis products were assessed by limiting-log10-dilution nested reverse-transcriptase polymerase chain reaction (RT-PCR) as one in 10(5) to one in 10(6) normal cells and were consistently undetectable in all purged PBSC autografts. We conclude that sufficient numbers of CD34+ cells for PBSCT can be collected after phase II but not at later stages of the GMALL 05/93 high risk protocol; PBSC grafts are 3 log less contaminated with residual BCR-ABL+ cells compared to an historical series of 13 autologous BM grafts; and purging of PBSC with mAb/IMB is feasible with minor loss of CD34+ cells and abolished BCR-ABL signals in the grafts.