Applicability and reproducibility of acute myeloid leukaemia stem cell assessment in a multi-centre setting

Leukaemic stem cells (LSC) have been experimentally defined as the leukaemia-propagating population and are thought to be the cellular reservoir of relapse in acute myeloid leukaemia (AML). Therefore, LSC measurements are warranted to facilitate accurate risk stratification. Previously, we published the composition of a one-tube flow cytometric assay, characterised by the presence of 13 important membrane markers for LSC detection

Relationship between CD34/CD38 and side population (SP) defined leukemia stem cell compartments in acute myeloid leukemia

Leukemic stem cells (LSCs), defined by CD34/CD38 expression, are believed to be essential for leukemia initiation and therapy resistance in acute myeloid leukemia. In addition, the side population (SP), characterized by high Hoechst 33342 efflux, reflecting therapy resistance, has leukemia initiating ability. The purpose of this study is, in both CD34-positive and CD34-negative AML, to integrate both types of LSC compartment into a new more restricted definition. Different CD34/CD38/SP defined putative LSC and normal hematopoietic compartments, with neoplastic or normal nature, respectively, were thus identified after cell sorting, and confirmed by FISH/PCR. Stem cell activity was assessed in the long-term liquid culture stem cell assay. SP fractions harbored the strongest functional stem cell activity in both normal and neoplastic cells in both CD34-positive and CD34-negative AML. Overall, inclusion of SP fraction decreased the size of the putative CD34/CD38 defined LSC compartment by a factor >500. For example, for the important CD34+CD38- LSC compartment, the median SP/CD34+CD38- frequency was 5.1 per million WBC (CD34-positive AML), and median SP/CD34-CD38+ frequency (CD34-negative AML) was 1796 per million WBC. Improved detection of LSC may enable identification of therapy resistant clones, and thereby identification of novel LSC specific, HSC sparing, therapies

High class II-associated invariant chain peptide expression on residual leukemic cells is associated with increased relapse risk in acute myeloid leukemia

The presence of class II-associated invariant chain (CLIP) on leukemic cells is negatively associated with clinical outcome in untreated acute myeloid leukemia (AML). CLIP plays a role in the immune escape of leukemic cells, suggesting that it impairs the immunogenicity of minimal residual disease (MRD) cells causing a relapse. Here, we demonstrate that CLIP expression on leukemia-associated phenotype (LAP)-positive cells during follow-up is significantly correlated with a shortened relapse-free survival, even in those patients who are generally considered as MRD(low) (0.01-0.1% LAP(+) cells). Consequently, CLIP evaluation could be of additional value in the evaluation of MRD to predict a relapse of AM