IFISH analysis of native smears from bone marrow and blood for the monitoring of chimerism and clonal markers after stem cell transplantation in children

After stem cell transplantation (SCT) close follow-up of chimerism and/or clonal disease markers is essential for early treatment of graft failure or relapse. We wanted to assess the sensitivity, clinical reliability and practicability of inter-phase FISH on untreated, native smears of BM or PB for this purpose. We investigated 23 children after SCT with sex mismatch (MM) and/or clone specific markers (monosomy 7, trisomy 8, MLL rearrangement, bcr-abl, TEL-AML-1). Diagnoses were ALL (8), AML (6), MDS (2), CML (2), large cell anaplastic lymphoma (1) and SAA (4). Eighteen children were transplanted from sex-mismatched donors, seven among them had shown a clonal marker at diagnosis. The remaining five patients with sex matched donors also had a clonal marker. For FISH, we used commercial probes on fresh or stored unmanipulated smears of PB or BM. Cut-off levels for clonal markers were established on control probands without hematologic disease, for host sex on probands of the opposite sex, respectively (mean +3 SD). The presence of host cells and/or clonal markers established at diagnosis by conventional karyotyping was followed up after SCT at regular intervals by FISH. Nineteen of the 23 patients studied achieved and maintained complete continuous hematologic remission with corresponding absence of host and/or disease markers. In one of them, a fatal extramedullary relapse occurred. The associated mixed chimerism was confirmed by FISH. In all four cases with hematological relapse, the respective marker (MLL, bcr-abl, Mo 7) reappeared and was successfully monitored during DLI and repeat SCT in two as well as parallelled by simultaneous demonstration of host cells in the two sex mismatched cases among them. We demonstrate the usefulness of FISH on native smears for clinical routine follow-up of SCT patients. FISH allowed identification of cell origin in non-hematologic material (spinal fluid, pericardial effusion). Chimerism analysis in BM was slightly more sensitive than in PB. FISH was feasible on frozen stored smears as well.