From the Guidelines
Chimerism can be effectively checked through cytogenetic analysis, specifically G-banded chromosome analysis, which is the preferred methodology for assessing the presence of donor and recipient cells in patients who have undergone allogeneic hematopoietic cell transplantation 1.
Key Considerations for Chimerism Testing
- The approach to checking chimerism involves analyzing 20 cells to determine the presence of donor and recipient cells, with specific guidelines for documentation based on the presence of only donor cells, both donor and recipient cells, or only recipient cells 1.
- In cases of sex discordant transplant, interphase FISH analysis using centromeric probes for the X and Y chromosomes can be used to determine the percentages of donor and recipient cells, although this method may have limited sensitivity 1.
- Cytogenetic analysis can uncover evidence of chimerism based on sex chromosome complement in the case of sex discordant transplant and in the rare instance of a constitutional structural chromosomal abnormality or an obvious chromosomal polymorphism in either the donor or recipient cells 1.
Clinical Application and Monitoring
- Monitoring of chimerism is crucial for transplant patients, as declining donor chimerism or mixed chimerism early after hematopoietic stem cell transplantation (HSCT) can be signs of imminent relapse 1.
- Techniques such as short tandem repeat (STR) analysis, fluorescence in situ hybridization (FISH), or quantitative PCR can be used to monitor chimerism levels in transplant patients, with peripheral blood samples typically drawn at scheduled intervals 1.
- The testing process requires comparing the recipient's pre-transplant DNA profile with post-transplant samples to calculate the percentage of donor versus recipient cells, which is essential for assessing the risk of graft rejection or disease relapse 1.
From the Research
Methods for Checking Chimerism
- Chimerism can be checked using various methods, including:
- Short Tandem Repeats (STRs) PCR, which is considered the gold standard method for chimerism quantification 2
- Quantitative PCR (qPCR), which has higher sensitivity than STR-PCR and can detect residual recipient DNA in patients with complete chimerism by STR-PCR 2, 3, 4
- qPCR using Indel markers, which is a standardized and sensitive method for chimerism analysis 5, 6
Sensitivity and Accuracy of Chimerism Testing Methods
- qPCR has been shown to be more sensitive than STR-PCR, with a positivity threshold of 0.1% compared to 1% for STR-PCR 3, 4
- STR-PCR is less accurate than qPCR for patients in mixed chimerism, but is more accurate for patients with complete chimerism 3
- The choice of method depends on the patient's chimerism status, with qPCR being more suitable for patients with complete chimerism and STR-PCR being more suitable for patients with mixed chimerism 3
Clinical Application of Chimerism Testing
- Chimerism testing is used to monitor engraftment and risk of relapse after allogeneic hematopoietic stem cell transplantation for hematologic malignancies 3, 4
- qPCR can detect residual recipient chimerism in patients with complete chimerism by STR-PCR, which can be a surrogate indicator of measurable residual disease 3, 4
- Chimerism testing can guide treatment decisions, such as the use of donor lymphocyte infusions for the treatment of persistent mixed chimerism or relapse 4