It is still unclear whether individuals with mixed chimerism after BMT have an increased risk of developing leukemic relapse or graft rejection [1,3,7,10,12,15, 16]. To address this question, we studied nine patients for chimerism after BMT (six sex-mismatched BMT and three sex-matched BMT). Unfortunately, two of the three sex-matched BMT patients did not allow us to draw any conclusions due either to an uninformative marker or death of the patient before analysis. The third patient revealed chimerism once but since our method was not quantitative it was not clear whether it was NCC or MC. The loss of chimerism later on in the patient was accompanied by a relapse and was perhaps due to the HLA mismatching BMT.
All six sex-mismatched BMT patients were successfully tested by FISH. Complete chimerism was found in only one patient after allogeneic BMT and he did not experience graft failure [12,15,16]. Nearly complete chimerism was detected in three cases. In all of these, the percentage of donor cells decreased to MC and the patients experienced relapse and graft failure. In one patient, low-level mixed chimerism (MC) that progressed to high-level MC, accompanied by full remission, was found. One patient showed low-level MC followed by complete loss of chimerism.
In all patients, the percentage of chimeric cells correlated with clinico-hematological data for remission or relapse. Therefore, our results confirm literature data that dynamic changes in chimerism have clinical and predictive value for the hematological status of the patients [1,3,7,12,15,16]. We conclude that the data from molecular detection of chimerism correlate with clinico-hematological findings of remission or early relapse of disease, and that FISH is a rapid and sensitive method for monitoring chimerism after sex-mismatched allogeneic bone marrow transplantation.