Tracking C-type lectin-like receptor positive leukemic stem cells to determine therapeutic efficacy in acute myeloid leukemia.

Abstract

e19011 Background: Although the importance of leukemia stem cells (LSC) in disease course of acute myeloid leukemia (AML) is well established in basic research, detecting and tracking LSC is seldom adopted in routine clinical practice. This is partly due to difficulty in tracking LSC in routine clinical practice and the paucity of evidence to support the benefit of detecting LSC in guiding clinical practice. Recently, a functional LSC population has been methodically characterized immunophenotypically, and the C-type lectin-like receptor (CLL1; aka CD371) has been shown to be widely expressed on LSC but not on normal hematopoietic stem cells (HSC). We postulate that CLL1 can be used to track LSC in a clinical setting and by analyzing changes in the LSC Compartment, we may be better able to assess response to therapy. Methods: Bone marrow samples from non-M3 CD34+ AML patients that were positive for CLL1 expression were included. Flow cytometry data were retrospectively analyzed for CLL1 percent positivity in the HSC compartment, which was defined as the CD34+CD38low/- fraction. A chart review was conducted to determine correlation between CLL1 positive LSC compartment change and clinical outcome. Statistical analysis was performed using GraphPad Prism version 9. Results: From 12/2018 to 12/2021, 49 AML cases with both pre- and post-treatment data from a single institution, were identified for the study. Among them, fourteen patients with CLL1 positivity higher than 50% were analyzed for CLL1+/HSC fractional change between pre- and post-treatment. We found that 6 of these 14 patients with significant reduction in CLL1+/HSC achieved longer remission, while the other 8 patients with no significant decrease in the CLL1+/HSC fraction demonstrated no or only a temporary remission. Importantly, several cases of patients with significant reduction in CLL1 positive cells will be presented to highlight the fact that LSC fractional change was more accurate in evaluating therapeutic effects and more predictive of clinical outcome than traditional morphology and flow cytometric analysis. This may even alter interpretation of specific treatment outcomes by predicting, for example, the brief nature that can be expected from certain remissions. Lastly, the CLL1+/HSC compartment in the peripheral blood is highly correlated with that of the bone marrow, indicating future feasibility of tracking LSC fractional change non-invasively to guide therapeutic decisions. Conclusions: CLL1 as a LSC marker is readily applicable to the clinical setting. Tracking LSC before and after AML treatment provides critical information regarding therapeutic effects that can sometimes be missed by traditional morphological and flow cytometric analysis. Thus, measuring changes in the LSC compartment using CLL1 analysis should be incorporated routinely in clinical practice to guide therapy decisions.