Evaluation of mixed chimerism in bone marrow transplantation program in Croatia

In this study we monitored mixed chimerism in 36 patients with various hematologic disorders. All of them underwent a classic conditioning regimen, 31 patients for related bone marrow transplantation (BMT) and 5 patients for unrelated BMT. DNA was isolated from peripheral blood, and samples were polymerase chain reaction (PCR) amplified for 5 short tandem repeat (STR) loci (TH01, VWA31, FES/FPS, F13A01, and SE33) and for one variable number of tandem repeats locus (D1S80). Samples were run on a 6% polyacrylamide gel in an automated ALFexpress sequencer. In all 36 donor-recipient pairs we found differences for at least two STR loci. In most cases the difference was observed for SE33 and D1S80 loci. Mixed chimerism (MC) was detected in 18 patients: 4 with unrelated BMT and 14 with related sibling donors. In 11 patients MC was detected in the early period after BMT, but was soon followed by full donor chimerism (FDC) in peripheral blood. In 5 cases patients MC appearing after FDC was established, and was predictive for the relapse. One patient showed alternating MC and FDC, but at the end showed only recipient cells and graft rejection. In conclusion, the PCR-STR analysis is a highly informative, fast, and simple screening method for monitoring chimerism in a BMT program.