Detection of host cells following sex-mismatched bone marrow transplantation by fluorescent in situ hybridization with a Y-chromosome specific probe.

Fluorescent in situ hybridization (FISH) with a biotinylated Y-chromosome specific repetitive DNA probe was applied to detect Y-bearing cells in blood and bone marrow samples from patients with hemopoietic malignancies after a sex-mismatched bone marrow transplantation. The sensitivity of this method is in the order of 0.1% Y-bearing nuclei in male recipients transplanted with female marrow. In female recipients of male marrow, the detection of low numbers of non-Y-bearing nuclei is less sensitive. The presence of host cells in blood and bone marrow of seven patients (four males, three females) was investigated with respect to successful engraftment or recurrence of the disease. The results obtained were compared with cytology (all seven cases) and with conventional cytogenetics (five cases). In five patients, the results of Y-FISH and cytology were identical. In two patients, low numbers of male host cells were detected in the marrow by Y-FISH, whereas cytology indicated complete remission of the disease. In three patients Y-FISH and cytogenetic data were similar, but in two patients Y-FISH revealed the presence of 0.2% and 7% male host cells, respectively, in bone marrow, whereas cytogenetics indicated a 100% female marrow in both cases. Because the hybridization was performed in situ, the morphology of the nuclei was preserved. To differentiate between normal and leukemic cells, the size of the blast cell nuclei appeared to be a very useful indicator. Our data suggest that fluorescent in situ hybridization with a Y-chromosome specific probe is a fast and sensitive technique to identify the host cells after sex-mismatched bone marrow transplantation, in particular in case of male recipient and female donor combinations.