Purging in BCR-ABL-positive acute lymphoblastic leukemia using immunomagnetic beads: comparison of residual leukemia and purging efficiency in bone marrow vs peripheral blood stem cells by semiquantitative polymerase chain reaction

Twenty autologous bone marrow (BM) and 25 peripheral blood stem cell (PBSC) grafts were collected from a total of 40 consecutive patients with BCR-ABL (+) acute lymphoblastic leukemia (ALL) in first (n = 37) or second (n = 3) complete morphological remission and subsequently purged with a cocktail of anti-CD19, -CD10, AB4 MoAbs and immunomagnetic beads (IMB). Residual BCR-A BL-positive cells before purging were detected in 19 of 20 BM grafts at a m edian of 4 (range 0-6) logs and in 17 of 25 evaluable PBSC grafts at a medi an of 1 (range 0-3) log above the limit of detection assessed by a semiquan titative limiting log(10)-dilution RT-PCR (P < 0.0001). IMB purging deplete d a median of 2.5 (range 1-4) log of residual BCR-ABL(+) cells from BM and a median of 1 (range 0-2) log from PBSC grafts, achieving RT-PCR negativity in 1/20 BM and 12/25 PBSC grafts after purging. Cell recoveries were 62% a nd 86% (P < 0.0001) of MNC and 74% and 97% (P = 0.065) of CD34(+) cells aft er BM and PBSC purging, respectively. BM purging was superior using the tri ple MoAb cocktail which depleted 2.64 +/- 0.4 log (n = 14) compared to 1.6 +/- 0.4 log (n = 5) using the MoAb cocktail not including AB4 (P = 0.02). W e conclude that unpurged BM grafts contain 2-3 log more residual BCR-ABL(+) cells than unpurged PBSC grafts and that purging efficacy is superior in B M compared to PBSC grafts, but median titers in purged BM grafts still exce ed those in purged PBSC grafts.