Underestimation of recipient DNA in bone marrow by post-transplant chimerism analyses using DNA extracted from EDTA-collected aspirate samples in pediatric acute myeloid leukemia

Goals: Chimerism analysis (CA) is essential for post-transplant surveillance. DNA from bone marrow (BM) aspirates drawn into EDTA specimen tubes (EDTA-BM) is widely used for CA. Since EDTA-BM is subject to peripheral dilution, however, DNA from aspirate particle smears (PS-BM) might better represent BM chimerism status. In this regard, we evaluated the influence of BM sources on CA. Procedures: Study subjects were consecutive pediatric AML patients who had experienced relapse after allogeneic stem cell transplantation with the interval between CA before relapse (pre-relapse) and at relapse <6 months. We compared chimerism status at the 2 time-points by fluorescence PCR on STR markers using EDTA-BM vs PS-BM. Results: Eight patients were eligible for this study. The recipient DNA (%R) from EDTA-BM was 0% at pre-relapse in all except 2 with 1.6% and 1.3%, while %R using PS-BM revealed mixed chimerism in all 8, %R ranging 1.6-13.2% (median 3.75%). The %R from EDTA-BM was 0.9-79.3% at relapse (29.15%), while %R from PS-BM was 3.8-86.6% (60.15%). The difference of %R (Δ%R), %R[PSBM]-% R[EDTA-BM], was median 3.15% (1.6-13.2%) at pre-relapse and median 12.1% (2.1-60.7%) at relapse. Conclusions: Our study showed CA using EDTA-BM significantly underestimated %R. Our observation might have a ramification to other quantitative workup in hematologic malignancy.