Need for an accurate molecular diagnosis to assess the donor origin of leukemia relapse after allogeneic stem cell transplantation

Background and and Objectives. Leukemia relapse occurring in donor cells af ter allogeneic hematopoietic stem cell transplantation has been reported in rare cases. Cytogenetic analysis and molecular probing of variable number of tandem repeats (VNTRs) have been used to confirm this unusual event in t he few cases so far reported in the literature. The aim of this study was t o demonstrate that extensive molecular characterization of leukemic cells a t diagnosis and relapse may be necessary to many technical pitfalls possibl y leading to an erroneous diagnosis of leukemia relapse in donor cells afte r allogeneic transplantation. Design and Methods. We report the case of a 49-year-old man who received an allogeneic transplantation from his HLA-identical sister because of BCR-AB L(+) acute lymphoblastic leukemia (ALL), After having achieved complete hem atologic and molecular remission, two years later an overt leukemia relapse occurred with cytogenetic findings suggesting a leukemia relapse in donor cells. The donor or patient origin of leukemic cells at relapse was further investigated by fluorescence in situ hybridization (FISH) karyotyping, rev erse transcription (RT) polymerase chain reaction (PCR) analysis of BCR-ABL chimeric transcripts, PCR amplification of several VNTRs and the Y chromos ome-specific DYS14 sequence and finally by amplification, cloning and seque ncing of the CDRIII region of the immunoglobulin heavy chain (IgH) gene. Results. At the time of relapse, conventional and FISH karyotyping revealed the presence of a Phl+ chromosome and a female karyotype in all the 25 met aphases analyzed and FOR amplification of the Y chromosome-specific DYS14 s equence was negative. Moreover, the molecular evaluation of hematopietic ch imerism performed by the NZ-22 VNTR allowed us to demonstrate that at the t ime of relapse a consistent proportion of hematopoietic cells was of donor origin. However, the molecular cloning and sequencing of the CDRIII region of the immunoglobulin heavy chain (IgH) gene rearrangement in leukemic blas ts at diagnosis and relapse demonstrated their identity thus formally provi ng the patient origin of both leukemic clones. Interpretation and Conclusions. While the simplest interpretation of the ap parent female karyotype at relapse is the consequence of a loss of the Y ch romosome which in leukemic blasts took place along with duplication of an X -chromosome, this case strongly emphasizes the need for accurate and extens ive molecular characterization to prove the donor origin of a leukemia rela pse after allogeneic transplantation. (C) 2000 Ferrata Storti Foundation.