Engraftment monitoring can determine chimerism by cell type as hematopoiesis occurs in the bone marrow over time to produce myeloid, erythroid, and lymphoid cells.
Chimerism assessment involves comparing donor and patient peaks. Peaks are defined by the height and area determined by Sanger sequencing or capillary electrophoresis. The area under each peak is added up for the donor peaks and is divided by the total area of peaks (including the patient peaks). If the patient STRs are present, this will imply patient cells are being produced in the bone marrow, and the graft may be in jeopardy of failing if patient leukocytes recognize the graft as foreign. Patient peaks only increase the equation's denominator, which lowers the percentage of total chimerism. This implies the patient may need more immunosuppressant therapy to protect the graft.
Essentially, the total number of donor peaks are compared to the total number of patient peaks. These data points are plugged into the equation to get a percentage. The goal is 100% and implies the donor cells make up all of the DNA and therefore HLA. 0% implies a total graft failure and all DNA is from the patient. Successful engraftment should have no patient peaks.
In looking at the image on the right, there are pretransplant patient and donor peaks. These represent "who is who" for post-transplant analysis. The post-analysis reveals a higher peak of donor compared to patient peaks. The peak areas need to be used in the equation to determine the percentage of engraftment.
16. Kentzel, Ethan. "STR profiles for engraftment monitoring, simplified." 16 Apr 2021.
