Comparison of STR-PCR and real-time PCR chimerism assays.

DNA extracted from different cell mixtures was evaluated for recipient genotype fraction by both fluorescent-based STR-PCR and real-time PCR chimerism assays. Panels A, C, and E show the results obtained on 3 DNAs (until the 1.25% recipient cell fraction) with STR-PCR using the D21S11 marker. Recipient-specific alleles (black peaks) and donor-specific alleles (gray peaks) define peak areas proportional to each individual-genotype fraction. In this case, longer recipient genotype–specific alleles seem less efficiently amplified than shorter donor alleles. Panels B, D, and F show the results obtained with real-time PCR on 3 DNAs (until the 0.15% recipient cell fraction). As the recipient cell fraction decreased in amplified DNA, amplification curves of allelic marker S 09a, specific for recipient genotype (black dotted lines), shift to the right; by contrast, amplification curves of the allelic marker S 09b, specific for the donor genotype, shift slightly to the left. In fact, these specific amplifications were independently performed in real-time PCR assay, and the sensitivity level for minor genotype detection is greatly improved, compared with STR-PCR assay results (compare panels E and F).