In vitro amplification of hypervariable DNA regions for the evaluation of chimerism after allogeneic BMT

The role of mixed hematopoietic chimerism in engraftment and relapse after allogeneic BMT remains unclear. To better evaluate post-transplant chimerism we used polymerase chain reaction (PCR) in vitro amplification of four single locus simple repetitive DNA sequences, all of which vary extensively in their repeat number among different individuals: variable number of tandem repeats D1S80, APOB and D17S5, and the tetranucleotide repeat F8VWF. We tested 13 cases of CML, four of multiple myeloma (MM), three of ANLL and one of B-CLL. In a sequential analysis protocol with the different loci, the donor could be distinguished from the recipient in 14 of 20 (70%) pairs with the first marker used (D1S80). When a donor of opposite sex was involved, karyotyping and Y chromosome-specific PCR were also used. With the use of the four markers, chimerism was identified in all the pairs. Mixed chimerism was present in 5 patients, and complete chimerism in 15. No patients relapsed. The application of PCR for documenting post-transplant chimerism has several advantages over Southern blotting: increased sensitivity, use of small amounts of sample, ease of preparation of DNA, elimination of restriction enzyme analysis and of radioisotopes, and speed.