Quantification of donor microchimerism in sex-mismatched porcine allotransplantation by competitive PCR

The persistence of donor cells in recipient circulation and peripheral tissues post-transplantation has been demonstrated in solid organ allotransplantation and xenotransplantation models. Although this state of microchimerism has been postulated as the basis for graft acceptance, chimerism has not been directly linked to the maintenance of peripheral tolerance or prevention of rejection. Studies have demonstrated that the qualitative presence or absence of donor microchimerism bears no association with graft acceptance. Our preliminary work suggests that there is a threshold chimerism necessary for the induction of donor-specific hyporesponsiveness. Because the kinetics of donor cell accumulation and distribution in allograft recipients are largely unknown, quantitative analyses are needed to evaluate chimerism's significance to donor-specific tolerance. We developed a quantitative, competitive PCR assay to precisely measure the amount of chimerism in male to female transplant pairs by targeting the sex-determining region of the Y chromosome (SRY gene). Traditionally, this technique requires that serial known amounts of an SRY-specific competitive template (CT) be coamplified with a constant amount of sample DNA to determine the equivalence point of the relative band intensities of the PCR products. However, running a panel of PCRs with CT amounts above and below the equivalence point to generate a standard curve for every sample is laborious. Here we describe the generation of a single standard curve that permits the rapid and reliable quantification of microchimerism after coamplification of sample DNA with a single amount of CT.