Real-time quantitative Y chromosome-specific PCR (QYCS-PCR) for monitoring hematopoietic 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) involving a male patient and female donor, which represents approximately 25% of all cases. We developed a quantitative Y chromosome-specific PCR assay (QYCS-PCR) based on the DFFRY gene for the determination of hematopoietic donor chimerism. We analyzed blood and marrow samples from more than 40 patients at various time points after both standard and nonmyeloablative allogeneic HSCT. We found that real-time PCR combines extreme sensitivity, with a detection 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 techniques as bcr/abl-PCR and/or fluorescent in situ hybridization (FISH) analysis. In two relapsed patients, increasing numbers of Y-positive hematopoietic cells indicated recurrence of malignant disease prior to clinical confirmation. In conclusion, quantitative Y chromosome-specific PCR is a promising approach for monitoring the extent of chimerism in blood and other tissues after sex-mismatched hematopoietic stem cell transplantation (HSCT) or organ transplantation.