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.