Strategies to improve the estimation of donor chimerism

Background: Reduced intensity conditioning regimens in peripheral blood stem cell transplantation (PBSCT) result in a period of mixed chimerism. Its regular monitoring is important to the patient''s clinical assessment and measurement precision is essential to that process. ‘Stutter’ artefact peaks hinder chimerism estimation by mimicking minor proportions of DNA. We wished to assess the value of adding more loci to our current protocol and to look at the value of selecting only those markers unaffected by stutter artefact. Methods: Donor chimerism was monitored in 32 patients post PBSCT on five occasions using the Profiler Plus (Applied Biosystems) and Powerplex 16 (Promega) short tandem repeat (STR) kits. Results: Mean donor chimerism was not significantly altered by increasing the numbers of loci, but precision increased significantly (p=0.0002). Removing loci affected by stutter from the Powerplex 16-associated measure increased error significantly (p=0.0024), due to decreased sample size. Conclusions: Increasing available autosomal loci from 9 to 15 has increased precision of chimerism measurement and the time-consuming selection of loci compromised by stutter position alleles has proved unnecessary. [Copyright &y& Elsevier]