Standardisation of multiplex fluorescent short tandem repeat analysis for chimerism testing

To evaluate the origin of cells after allogeneic haematopoietic stem cell t ransplantation we optimised and evaluated two commercially available system s (AmpFlSTR Profiler Plus and GenePrint Powerplex-16) which are based on mu ltiplex fluorescent short tandem repeat (STR) analysis. A standard procedur e for interpretation of electropherographs was found essential to obtain re producible results. On the basis of the relative length of donor and recipi ent alleles, TYPE-I (no shared alleles are used to calculate chimerism), TY PE-II (one shared and one unshared allele is used to calculate chimerism) o r TYPE-III (not informative) allelic distribution types were distinguished. Also, stutter peaks were recognised as an important criterion to exclude a marker for analysis. Intralaboratory and multicentre evaluation of the Amp FlSTR Profiler Plus system showed that mixed blood samples could be determi ned with an absolute deviation of less than 2%. A sensitivity threshold was set at 5% for TYPE-I and 10% for TYPE-II markers since relative imprecisio n increases at low chimerism values. No significant difference of calculate d chimerism values was observed between STR markers shared between both sys tems. By monitoring 26 allogeneic peripheral blood stem cell transplants, t he applicability of the proposed method was demonstrated.