Early detection of relapse and evaluation of treatment for mixed chimerism using fluorescence in situ hybridization following allogeneic hematopoietic cell transplant for hematological malignancies.

In order to detect chimerism, fluorescence in situ hybridization (FISH) and cytogenetic analyses were performed on bone marrow cells from 47 patients with hematological malignancies following allogeneic hematopoietic cell transplant (HCT). The dual-color XY, major Bcr-Abl (M-Bcr-Abl), and specific alpha-satellite probes were used for sex-mismatched HCT, chronic myeloid leukemia (CML), and myelodysplastic syndrome (MDS) cases with karyotypic abnormalities before HCT, respectively. Donor cells were found using FISH analysis in all 32 cases examined within 2 months following HCT, confirming engraftment. In six cases, however, cytogenetic analysis failed to detect donor cells due to lack of metaphases. Relapse occurred in four of the six cases in which mixed chimerism was detected using FISH analysis after 6 months of HCT. In contrast, after 12 months of HCT, no relapse was found in 24 patients without host cells. For two patients with mixed chimerism, gradual reduction of immunosuppressants or donor lymphocyte infusion resulted in the disappearance of host cells as analyzed using FISH analysis. In three extramedullary relapse cases, however, cytogenetic relapse preceded morphological and FISH relapse. These findings suggest that FISH analysis is more useful for detecting residual host cells after HCT, and the combination of FISH and cytogenetic analyses provide a more detailed evaluation for HCT patients. The results also indicate that monitoring of mixed chimerism using FISH analysis after 6 months of HCT is important for allowing the early detection of hematological relapse.