PB1759: RETAINED FUNCTIONAL NORMAL AND/OR PRE-LEUKEMIC HSCS IN THE BONE MARROW ARE ASSOCIATED TO GOOD PROGNOSIS IN DNMT3AMUTNPM1MUT AML PATIENTS

Topic: 3. Acute myeloid leukemia - Biology & Translational Research Background: Acute Myeloid Leukemia (AML) is a highly aggressive adult leukemia with a high incidence of relapse and mortality. AML hijacked the hierarchical organization of normal hematopoiesis with Leukemia Stem Cells (LSCs) at the top of the differentiation tree and differentiated and highly proliferating myeloid blast at the bottom. Similar to normal hematopoietic stem cells (HSCs), LSCs have been originally identified as CD34+CD38- cells. However, this strategy to isolate LSCs is particularly challenging in NPM1 mutated AMLs, since expression of CD34 on leukemic cells is low or absent altogether. Aims: In this study, we aimed to establish a novel sorting strategy to isolate LSCs independently of CD34 surface marker in both CD34positive and CD34negative AMLs. Methods: Using a genetically highly homogeneous cohort of 46 AML patients carrying DNMT3A and NPM1 mutations, we established a novel isolation strategy to enrich for LSCs even in CD34negative AMLs by additionally including a positive selection for GPR56 and a negative selection for mature markers such as NKG2DLigandss. Results: By combining functional in vivo data, mutational analyses on xenografts and transcriptomic data, we found that CD34+GPR56+NKG2DL- subpopulations can contain along with LSCs also normal and/or pre-leukemic (HSCs). In contrast, no such residual normal or pre-leukemic HSCs were detected in CD34-GPR56+NKG2DL- subpopulations. Finally, we show that naïve AML patients who retain a relevant reserve of normal and/or preleukemic HSCs, able to reconstitute immunocompromised mice at time of diagnosis, have significant longer relapse-free and overall survival compared to patients without engrafting HSCs. Summary/Conclusion: These data suggest that the presence of normal and/or preleukemic HSCs with multilineage engrafting potential in the bone marrow of naïve patients is associated with good response to standard chemotherapy, providing a basis for the development of novel predictive biomarkers for standard chemotherapy regime. Keywords: DNMT3A, AML, Leukemic stem cell, Stem cell marker