[Application of sequential and quantitative monitoring of chimerism in allogeneic hematopoietic stem cell transplantation].

Objective: To establish multiple short tandem repeat (STR) amplification by fluorescence labeling polymerase chain reaction (PCR) combined with capillary electrophoresis for quantitative determination of chimerism, and to evaluate the status of engraftment and predict the outcome of allogeneic hematopoietic stem cell transplantation (allo-HSCT).

Methods: Thirty-one patients received bone marrow transplantation (BMT) or nonmyeloablative allogeneic stem cell transplantation (NST) were evaluated. Peripheral blood and bone marrow were co-llected before and after transplantation in different period. Nine different STR markers were co-amplified in a single reaction by using a commercial AmpF/STR Profiler Plus PCR amplification kit. Separation of the PCR products and fluorescence detection were performed by ABI prism 310 Genetic Analyzer with capillary electrophoresis. The Genescan and Genotype software were used for size calling and quantification of peak areas. The formula to calculate donor chimerism values was based on the different allelic distribution type between donor and recipient.

Results: 48.4% of the patients received sex-matched transplantation and the quantification of donor chimerism could only be performed by STR-PCR method. Comparison of values obtained by FISH analysis with that by STR-PCR in patients transplanted from sex-mismatched donors showed an excellent correlation. The median number of informative alleles was 6.7 (range 2 - 10). The donor's alleles appeared in all the patients on day 7 post-transplant. The median values of donor chimerism in BMT group were inferior to that in NST group on day 7, day 14 and 1 month post-transplant. However the difference disappeared in the midterm or later period of transplant. On day 21, all of the 31 patients had stable engraftment and the percentage of donor chimerism was more than 92%. Median follow-up was 17 (3.5 - 29.0) months after transplantation. Twenty-six of 31 patients had durable engraftment and donor chimerism ratio was more than 90%. So for all of them survived leukemia-freely. Four of the 31 patients had unstable mixed chimerism and relapsed within 6 months post allo-HSCT. Another patient with unstable mixed chimerism appeared graft rejection. Decreasing values of donor chimerism were detected prior to the occurrence of graft rejection and disease relapse. The incidence of GVHD was much higher in the group of full donor chimerism.

Conclusion: Sequential and quantitative monitoring of STR is a valuable tool for studying engraftment dynamics, graft rejection, and relapse and for predicting GVHD. Furthermore it can provide a basis for early intervention of clinical treatment.