The role of available hematopoietic stem cell niches during leukemic and pre-leukemic engraftment

• Applicant: Dr. Thomas Köhnke
• Subject Area: Hematology, Oncology
• Term: from 2016 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 329524782

Acute myeloid leukemia (AML) is a clonal malignancy of myeloid progenitors associated with dismal prognosis. Our understanding of the clonal architecture of AML has improved markedly over the past years, revealing pre-leukemic "founder" clones harboring initial mutations within the hematopoietic stem cell (HSC) compartment which then acquire further mutations and ultimately lead to the development of AML. The penetration of the HSC-compartment with cells carrying pre-leukemic mutations shows high inter-individual variability. Importantly, while this inter-individual variability can be detected even in patients with the same mutations, the burden of pre-leukemic HSC is correlated with outcome for AML patients. This suggests that the ability of progenitors harboring pre-leukemic mutations to expand, but not the specific pre-leukemic mutations per se, is a critical feature of leukemogenesis.In previous work studying the engraftment of HSCs, efficient removal of recipient HSCs by administration of a depleting antibody targeting murine c-kit (ACK2) could greatly enhance the engraftment of donor HSCs, suggesting that the availability of "empty" niches is crucial for HSC engraftment. Based on these observations, we hypothesize that "empty" bone marrow niches allow for the expansion of pre-leukemic HSCs and predispose to the development of hematologic cancer including AML.To address this hypothesis, we will use several experimental approaches involving NSG mice. To detect whether pre-leukemic HSCs will outcompete normal HSCs when "empty" niches are made available, we will a) transplant primary HSCs from patients with AML displaying varying proportions of pre-leukemic and healthy HSCs and b) transplant a mixed population of lentiviral engineered GFP+ (pre-leukemic mutant transduced cells) and GFP- (non-transduced normal cells). In both approaches, mice will be treated with ACK2 to continually empty niches of mouse HSCs. To detect whether pre-leukemic HSCs will more likely progress to AML when "empty" niches are made available, primary HSCs will be transplanted as above and mice treated with ACK2. Then mice will be followed for up to 12 months for the development of leukemia. A plethora of techniques will be used to analyze the blood and bone marrow from these mice (e.g. immunophenotyping, cell sorting, histopathology, targeted sequencing, etc.) to assess the proportion of pre-leukemic HSCs and detect additional mutations associated with clonal evolution.Taken together, novel treatment approaches targeting residual pre-leukemic cells not eliminated by current treatment options are needed for patients with AML. An improved understanding of the role of "empty" HSC niches in the expansion of pre-leukemic HSCs and the development of AML will aid in our knowledge of the biology of the disease and might ultimately lead to the development of treatment approaches targeting pre-leukemic clones in AML.

• DFG Programme: Research Fellowships
• International Connection: USA
• Host: Professor Dr. Ravindra Majeti