Chimerism Status as a Possible Marker of Incipient Disease Relapse in Patients with AML.

The connection between chimerism status and occurence of relapse in patients undergoing hematopoietic stem cell transplantation remains controversial. One reason for this seems to be employment of different methods with inherrited different sensitivity and related definition of complete donor chimerism (CDC). We compared an application of fragment analysis (FA) of minisatellite, microsatellite or sex specific regions (limit of quantification ∼1%) with real-time quantitative PCR (RQ-PCR) of insertion/deletion and sex polymorphism (limit of quantification ∼0.1%). Long-term data (follow-up 1.8–7.4 years, median 3.3 years) obtained from two groups of AML patients transplanted in our centre are presented. The first group involves 9 patients that experienced relapse (one of them three times) whereas the second one contains 11 individuals in complete remission. Retrospective chimerism analysis of patients in the first group by RQ-PCR allowed prediction of hematological relapse significantly earlier (p=0.016) than quantification by FA, (35–448 days, median 77 days by RQ-PCR vs. 0–154 days, median 35 days by FA). Beside this, in two cases the incipient relapse was detected only by RQ-PCR and not by FA, 118 and 70 days in advance. Moreover, in two patients with fusion gene, there was detection of molecular relapse recorded simultaneously by either increase of autologous hematopoiesis or conversion of CDC to MC in granulocytes, as revealed by analysis of sorted leukocyte subsets. On the other hand, after achievement of CDC within the group of patients in complete remission, the amount of detectable autologous DNA did not repeatedly exceeded the limit of quantification of RQ-PCR. The CDC was not achieved in one case only, whereas lineage-restricted analysis persistently shows MC in T-lymphocytes (1–3% of autologous origin). Our data demonstrate, that assessment of chimerism by RQ-PCR along with analyses within specific leukocyte subsets can provide an early indication of incipient disease relapse of AML and could be used for residual disease monitoring in cases, where another specific marker is not available.