Bone marrow transplant relapse with loss of an allele

BackgroundDetection of the extent of chimerism after transplantation is an important method for monitoring the engraftment of donor stem cells or diagnosing relapse.MethodsThe AmpFlSTR Identifiler amplification kit (Applied Biosystem, CA) was used to perform STR-PCR for the study of engraftment.ResultsAt 6 months post-transplantation, the peripheral blood genotype shows a mixture of donor and recipient alleles, consistent with disease relapse. Interestingly, the D18S51 locus shows 2 donor alleles and only 1 recipient allele, the other recipient allele is missing. To further confirm chromosome loss, we used the D18S53 and D18S1129 in the ABI PRISM Linkage Mapping Sets. The D18S53 locus showed the recipient allele (179 bp) and shared allele (171 bp). Interestingly, the D18S1129 locus showed almost only 1 recipient allele (243 bp); the other recipient allele and shared allele (251 bp) is missing.ConclusionThe case illustrates that chromosome loss in tumor cells during the course of disease may cause corresponding loss of an STR locus. This circumstance is a potential source of error in the interpretation of engraftment analysis, especially if only one informative allele is used to monitor engraftment.