Real-time quantitative y chromosome-specific PCR (QYCS-PCR) for monitoringhematopoietic chimerism after sex-mismatched allogeneic stem cell transplantation

Y chromosome-specific sequences can be used to detect remaining male cells after sex-mismatched allogeneic blood stem cell transplantation (HSCT) invo lving a male patient and female donor, which represents approximately 25% o f all cases. We developed a quantitative Y chromosome-specific PCR assay (Q YCS-PCR) based on the DFFRY gene for the determination of hematopoietic don or chimerism. We analyzed blood and marrow samples from more than 40 patien ts at various time points after both standard and nonmyeloablative allogene ic HSCT. We found that real-time PCR combines extreme sensitivity, with a d etection level of less than 1 male in 100,000 female cells (<0.001%), with very good reproducibility, especially in the important range of minor host chimerism. QYCS-PCR results were in close agreement with data from other te chniques as bcr/abl-PCR and/or fluorescent in situ hybridization (FISH) ana lysis. In two relapsed patients, increasing numbers of Y-positive hematopoi etic cells indicated recurrence of malignant disease prior to clinical conf irmation. In conclusion, quantitative Y chromosome-specific PCR is a promis ing approach for monitoring the extent of chimerism in blood and other tiss ues after sex-mismatched hematopoietic stem cell transplantation (HSCT) or organ transplantation.