IMMUNOMAGNETIC BONE-MARROW PURGING IN CHILDREN WITH ACUTE LYMPHOBLASTIC-LEUKEMIA

Autologous bone marrow transplantation (ABMT) offers a therapeutic alt ernative for children with poor prognosis acute lymphoblastic leukemia (ALL) who lack an HLA-matched sibling donor. The most common cause of treatment failure after ABMT in these patients is leukemia relapse. W e have developed an ex vivo autologous marrow purging program for chil dren with ALL using an immunomagnetic method. BM purging has been perf ormed in 37 children with ALL (31 B-lineage ALL and 6 T-lineage ALL) f ollowing an indirect method, using panels of mouse monoclonal antibodi es (MAbs) directed against B or T cell antigens, Dynabeads M-450 (Dyna l) coated with sheep antimouse (SAM) antibodies, and the MaxSep(TM) Ma gnetic Cell Separator (Baxter). Purging efficiency has been assessed b y flow cytometry. Considering the limit of detection of target cells 0 .1%, the median depletion was 2.0 log (range 0.8- > 2.8 log) for the B -lineage ALL and 2.7 (range 2.2- > 2, 9 log) for the T-lineage ALL pat ients. Twenty-seven patients have been autografted (6 in first complet e remission, CR, 13 in second CR, and 8 in third or subsequent CR). En graftment has been satisfactory in all of them, reaching levels of 500 neutrophils/mm(3) and 20,000 platelets/mm(3) after a median of 17 (ra nge 12-39) and 30 (range 13-96) days post-ABMT, respectively. In summa ry, our results show that this immunomagnetic procedure achieves high levels of target cell depletion and can be safely applied to bone marr ow purging in childhood ALL patients.