Sequential monitoring of chimerism and detection of minimal residual disease after allogeneic blood stem cell transplantation (BSCT) using multiplex PCR amplification of short tandem repeat-markers

Sequential analysis of chimerism after allogeneic blood stem cell transplan tation (BSCT) has been shown to be predictive for graft failure and relapse . We have explored the impact of a novel approach for the quantitative dete rmination of chimerism using a commercial PCR assay with multiplex amplific ation of nine STR-loci and fluorescence detection. The feasibility was stud ied in 121 patients transplanted from related or unrelated donors. Follow-u p investigation was performed in 88 patients. Twenty-eight of these patient s had received a transplantation after dose-reduced conditioning therapy. R esults were compared to data obtained by FISH analysis in a subgroup of pat ients receiving grafts from sex-mismatched donors. The analysis was possibl e in all patients, the median number of informative alleles was 4 (range 1- 8) compared to 7 (range 19) in the related and unrelated situation, respect ively. A good correlation was seen in 84 samples from 14 patients analyzed in parallel with STR-PCR and FISH. Decreasing values of donor chimerism wer e detected prior to or concomitantly with the occurrence of graft failure a nd relapse of disease in all patients investigated prospectively, Using FAG S-sorted material, eg peripheral blood CD34(-) cells, the assay permitted t he detection of residual recipient cells with high sensitivity (down to one CD34(+) Kasumi cell in 40 000 normal WBC), Evaluation of the inter-laborat ory reproducibility revealed that in 20 samples analyzed in three different centers, the median coefficient of variation was 2.1% (range 0.7-9.6%). Ta ken together, the results support the use of the test as a valuable tool in the follow-up of patients undergoing allogeneic BSCT. In cases lacking PCR -detectable disease-specific gene products, this assay may represent an alt ernative to recently established real-time PCR methods.