Objective: An important step in successful autografting of patients with chronic myelogenous leukemia is the delivery of a leukemia-free graft. We conducted this study to determine whether the cytogenetic response after autografting was correlated with the number of BCR ABL-positive cells present within the stem cell grafts.
Materials and methods: By BCR-ABL mRNA quantification, we studied the serial pheresis products from 40 Philadelphia (Ph)-positive patients who received ICE/mini-ICE mobilization therapy and underwent autologous stem cell transplantation. We correlated the residual disease within the graft reinfused with the cytogenetic response following transplantation, taking into consideration those responses that lasted 12 months or more.
Results: Thirty-two patients received a graft with 0-35% Ph-metaphases and 19 received a graft with BCR-ABL/ABL ratio < or =0.01. After a median of 27 months (range, 12-50) from transplant, 18 patients achieved complete or major cytogenetic response lasting at least 12 months, and 14 of them (78%) received a graft with BCR-ABL/ABL ratio < or =0.01 (range, 0.0003-0.01). Twenty-two patients experienced short-lived responses or had >35% Ph-positive cells in the marrow after transplant, but only 5 of them (23%) had a graft with BCR-ABL/ABL ratio < or =0.01 (range, 0.001-0.01). Therefore, we found a strong association between a BCR-ABL/ABL ratio less than or =0.01 and the achievement of complete or major cytogenetic remission after autografting (chi(2) test, p = 0.0001). Patients reinfused with grafts contaminated at low levels with leukemic cells also showed a longer duration of the response (log-rank test, p = 0.0009). Eleven patients were reinfused with the lowest level of contaminated stem cell collections, according to the BCR-ABL/ABL ratio. None of these patients experienced prolonged neutropenia or thrombocytopenia following stem cell reinfusion and nine of them had long-lasting complete or major cytogenetic responses after transplant.
Conclusion: This study demonstrates that the number of BCR-ABL positive cells present in a stem cell graft is an important predictive factor for the achievement and the duration of cytogenetic response after autografting. [corrected]