Genetic fingerprinting in mouthwashes of patients after allogeneic bone marrow transplantation

Detection of chimerism by PCR analysis of short tandem repeats (STR) in blood samples of patients who received allogeneic bone marrow transplantation (BMT) has proved to be an important method for early detection of relapse. The prerequisite for this type of analysis is knowledge of donor and recipient pretransplantation genotypes, In some cases, recipient cells from time points prior to BMT are not available and the pretransplant fingerprint cannot be determined. As BM recipients only alter their genotype in blood cells, we attempted to identify patient's pretransplantation genotypes after transplantation in mouthwash samples that contain easily accessible epithelial cells. Of 17 patients who had undergone BMT between one week and 45 months prior to analysis, DNA was isolated from mouthwash cell pellets or from epithelial cells obtained from mouthwashes, PCR analysis of STR loci in the von Willebrand and the tyrosine hydroxylase genes were performed, Even though the mouthwash cell pellets contained about 75% epithelial cells (presumably of recipient origin) and only about 25% leukocytes (presumably of donor origin), three of five patients showed donor genotype and only two patients exhibited chimeric DNA patterns, when cellular DNA was obtained by boiling of mouthwash cell pellets. Following phenol/chloroform extraction, eight of 10 DNA samples exhibited a chimeric pattern, while two of 10 DNAs showed only donor genotype, Of three patients, epithelial cells were attached to magnetic beads prior to DNA isolation. Even this DNA contained donor and recipient material. From our results it appears that blood cells serve as preferential DNA source in mouthwash samples and cannot be removed by epithelial cell separation.