Molecular analysis of relapse in chronic myeloid leukemia after allogeneic bone marrow transplantation.

Four patients with Philadelphia (Ph') positive chronic myeloid leukemia (CML) were studied before, after, and on relapse following allogeneic bone marrow transplantation (BMT). Southern analysis of DNA from cells collected before and at relapse after BMT was performed in order to investigate the origin of the leukemia at relapse. Using minisatellite probes we showed that the relapse occurred in cells of host origin in all four patients and this was confirmed with a Y chromosome specific probe in two male patients who had a female donor. Furthermore, using two probes for the breakpoint cluster region (bcr) on chromosome 22, we showed that leukemic cells at relapse bore identical rearrangements to those in the disease at time of presentation of each patient. We conclude that relapse in all four patients is due to re-emergence of the original leukemic clone.