THE EVALUATION OF MIXED CHIMERISM IN BONE MARROW TRANSPLANTATION PROGRAM IN CROATIA

Abstract

P1157 Aim: Mixed chimerism (MC) is a state in which there is a presence of both recipient and donor haematopoietic cells and is frequently observed after bone marrow transplantation (BMT). Previous studies have used cytogenetic techniques, changes in erytrocyte phenotype or RFLP analysis for following chimerism. In cases when none of these markers is useful, analysis of short tandem repeat (STR) loci can be potential diagnostic tool. Material And Methods: In this study we monitored 27 patients suffering from various haematological disorders. Twenty-four of them underwent classical conditioning regimen (21 patients for related BMT and 3 patients for unrelated BMT). The remaining 3 patients were subjected to nonmyeloablative conditioning (minitransplantation). DNA samples were PCR amplified for 5 STR loci (TH01, VWA31, FES/FPS, F13A01, and SE33) and for one VNTR locus (D1S80). In the cases of minitransplantation or when only one of six previously mentioned loci was informative, additional 4 STR loci (D1S1656, D12S391, D18S535, and D22S683) were also tested. Samples were run on a 6% polyacrylamide gel in an automated ALFexpress sequencer. Results: In all 27 donor-recipient pairs we found differences for at least two STR loci. In most cases the difference was observed for SE33 and D1S80 loci. MC was detected in a total of twelve patients: 3 cases of minitransplantation, 3 cases of unrelated BMT and six cases with related sibling donor. MC was predictive for the relapse in two out of twelve patients. The first case was the patient who received full HLA matched unrelated bone marrow. Full donor chimerism was found until day 160 after BMT, when 40% of recipient cells were detected. The second case was the patient who received HLA identical bone marrow from his sister. The starting ratio between donor and recipient cells was 30:70. The percentage of donor cells grew up, reaching 100% at day 50 after BMT. However, ten months after BMT 40% of recipient cells were detected in peripheral blood, which was predictive for the relapse of disease. Conclusion: The PCR-STR analysis is a highly informative, fast and simple screening method for monitoring chimerism in BMT program. The possible value of MC as an indicator of relapse should be verified in the larger group of patients.