Diagnostic value of highly-sensitive chimerism analysis after allogeneic stem cell transplantation

Abstract

Conventional analysis of host chimerism (HC) frequently fails to detect relapse before its clinical manifestation in patients with hematological malignancies after allogeneic stem cell transplantation (allo-SCT). Quantitative PCR (qPCR)-based highly-sensitive chimerism analysis extends the detection limit of conventional (short tandem repeats-based) chimerism analysis from 1 to 0.01% host cells in whole blood. To date, the diagnostic value of highly-sensitive chimerism analysis is hardly defined. Here, we applied qPCR-based chimerism analysis to 901 blood samples of 71 out-patients with hematological malignancies after allo-SCT. Receiver operating characteristics (ROC) curves were calculated for absolute HC values and for the increments of HC before relapse. Using the best cut-offs, relapse was detected with sensitivities of 74 or 85% and specificities of 69 or 75%, respectively. Positive predictive values (PPVs) were only 12 or 18%, but the respective negative predictive values were 98 or 99%. Relapse was detected median 38 or 45 days prior to clinical diagnosis, respectively. Considering also durations of steadily increasing HC of more than 28 days improved PPVs to more than 28 or 59%, respectively. Overall, highly-sensitive chimerism analysis excludes relapses with high certainty and predicts relapses with high sensitivity and specificity more than a month prior to clinical diagnosis.

Highly sensitive chimerism detection in blood is associated with increased risk of relapse after allogeneic hematopoietic cell transplantation in childhood leukemia

“…On the one hand, an increase in recipient peripheral blood DNA at the low level of 0.05% carries a risk of a higher number of false‐positive results . On the other hand, only 5 out of 15 children in our study who eventually relapsed had a single IMC above 0.1%.…”

“…The obvious challenge in establishing applicable cutoff levels is related to the need to balance early detection with avoiding unnecessary treatment in the case of false‐positive results. The increased sensitivity of the RQ‐PCR chimerism analysis as compared to STR‐PCR implies that previously undetected fluctuations of recipient DNA are detected . Recipient DNA in low levels could be caused by surviving leukemic blasts, host hematopoietic cells, cells of non‐hematopoietic origin, or a combination of these.…”

“…Recipient DNA in low levels could be caused by surviving leukemic blasts, host hematopoietic cells, cells of non‐hematopoietic origin, or a combination of these. Most studies of RQ‐PCR chimerism have used absolute detection levels of 0.1%‐1% recipient DNA as clinically relevant cutoffs, although results from definitions based on increasing donor DNA rather than absolute levels have been reported in adults . In our study, we detected stable recipient DNA at least once during follow‐up in all children and 56% (347/610) of samples had values above detection limit.…”

“…Thus, detection of very small increases of 0.05% could guide identification of children at higher risk of relapse that would be eligible for an intensified follow‐up including MRD analysis in bone marrow. This is in line with previous studies reporting high negative predictive values, and relatively low positive predictive values for RQ‐PCR chimerism …”

“…This is in line with a previous study of adults, reporting an association with relapse and chimerism at day + 90 post‐HCT, but not with chimerism day + 30 . Interestingly, a recent study reported association between viral infections and early IMC, possibly reflecting proliferation of antiviral T cells of recipient origin . It could seem contradictory that IMC in our data is highly predictive of relapse, while no association could be found when examining only RQ‐PCR chimerism during the first 90 days post‐HCT.…”