Genetic Instability in Remission Hematopoiesis Is Different from That in AML Blasts: A New Diagnostic Tool to Study Biology of AML.

Recently we have shown that aberrations, ie microsatellite instability (MSI) and allelic imbalance (AI) in positively selected CD34+ cells from leukapheresis products collected during first complete remission of de novo AML following double induction or consolidation according to AMLCG protocol may be predictive for relapse-free survival (RFS). Here we present data of an extended patient population treated on the same protocol. We compared MSI/AI pattern in CD34+ cells (n=60) with the corresponding pattern in AML blasts at diagnosis (n=60) or at relapse (n=12), and compared the AI/MSI pattern in CD34+ cells with those observed in the corresponding unselected bone marrow aspirates in first CR (n=50). The following loci were tested: D7S486, D7S525, D8S559, TP53, D11S1356, D2S123, APC, MfD5. Minimal residual disease (MRD) in the tested remission specimen (FACS analysis) was <0.1%. MSI and/or AI at diagnosis could be detected in few cases (10 of 60, 17%), whereas CD34+ cells were tested positive in 25 of 60 cases (42%), and in 5 of 12 relapses studied (42%). Analysis of AI and MSI in DNA of bone marrow aspirates could not adequately confirm MSI and/or AI detectable in the corresponding CD34+ cells (n=3 cases, 12%). In 15 cases MSI and/or AI was observed in CD34+ cells, but not in AML blasts at diagnosis, in 5 cases in blasts at diagnosis, but not in CD34+ cells, in 4 cases in AML blasts at diagnosis and in CD34+ cells. Identical AI/MSI pattern were found in CD34+ cells and in AML blasts at relapse (n=2), as well as in AML blasts at diagnosis and relapse (n=1). According to the definition of genetic instability (GIN: MSI or >2 AI at any locus, AI at APC locus), GIN in CD34+ cells was predictive for unfavorable RFS (p=0.001). In conclusion, detection of AI/MSI in CD34+ cells of remission hematopoiesis represents a new important diagnostic tool to study biology of AML besides the detection of MRD. For the first time we could demonstrate, that the same AIs or MSIs detectable in CD34+ cells, but not in AML blasts at diagnosis may occur in AML blasts at relapse.