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 leu kemia (ALL) achieving clinical remission (CR) after induction or conso lidation chemotherapy according to the German multicenter adult ALL (G MALL) protocol showed high titers of residual BCR-ABL(+) cells. Theref ore, we initiated a pilot study to monitor circulating BCR-ABL(+) cell s and to collect, purge, and autograft peripheral blood stem cells (PB SC) in these patients. After GMALL 05/93 high-risk phase II of inducti on chemotherapy (high-dose AraC 3 g/m(2) x 8 doses and mitoxantrone 10 mg/m(2) x 3 doses), patients received 5-10 mu g/kg subcutaneous recom binant human granulocyte colony-stimulating factor (rhG-CSF) daily. Mo bilized CD34(+) cells peaked between 20 and 26 days after starting che motherapy 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 m obilize adequate numbers of CD34(+) cells. PB stem cells (PBSC) were p urged using a cocktail of CD10, CD19, and AB4 monoclonal antibodies (m Abs) coupled to immunomagnetic beads (IMB). The median recoveries of t otal nucleated cells (TNC) and CD34(+) cells after mAb/IMB purging wer e 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 postp urge (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(+) cell s in unpurged leukapheresis products were assessed by limiting-log(10) -dilution nested reverse-transcriptase polymerase chain reaction (RT-P CR) as one in 10(5) to one in 10(6) normal cells and were consistently undetectable in all purged PBSC autografts. We conclude that sufficie nt 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 gr afts are 3 log less contaminated with residual BCR-ABL(+) cells compar ed 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 abo lished BCR-ABL signals in the grafts.