Quantitative assessment of clonal architecture, stem cell competition and lineage fate in CH (Project B2)

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Clonal hematopoiesis (CH) occurs by the acquisition of somatic mutations in recurrent leukemia-associated genes in hematopoietic stem cells (HSCs). These CH driver mutations cause a fitness and growth advantage of CH-mutated over non-mutated HSCs by various mechanisms, which are further orchestrated by intrinsic regulation and extrinsic environmental factors. Many studies revealed a clinical association of the presence of CH mutations and the affected mutant clone size in blood cells, and their risk to aggravate cardiovascular diseases and to progress into hematologic malignancies. Therefore, understanding the pathomechanisms of clonal dominance and growth caused by mutations in the most relevant CH driver genes is of utmost importance for early prevention and clinical management strategies. In close collaboration within the Research Unit HERZBLUT we want to study the clonal architecture, dominance and interference at single clone and cell level, using innovative cellular barcoding and single cell sequencing technologies in mouse and human CH-mutated HSC development. We will investigate and compare the mechanisms that are caused by two highly prevalent classes of CH-mutated genes, in the splicing factor genes SRSF2 and SF3B1 and in the epigenetic modifier genes DNMT3A and TET2. In particular, CH mutations in SRSF2 and SF3B1 are associated with a high stem cell fitness score and accelerated risk to aggravate CH-related diseases. We aim to study first 1) the clonal competition, local distribution, and differentiation behavior of CH-mutated HSCs in syngeneic CH mouse transplantation models and in in vitro differentiation assays at single cell resolution. Therefore, we will apply lentiviral barcoding, single cell sequencing and time-lapse microscopy-based single cell tracking to quantitatively assess CH-mutated clonal outgrowth and behavior. 2) Second, we will investigate changes in the molecular and metabolic profile of CH-mutated HSCs by linking cell state with cell fate. To this end, we have developed barcode-based paired daughter assays to understand molecular correlations between the cell of clonal origin (state) and its future differentiation behavior (fate). We will investigate the link between mitochondrial potential, energy metabolism and dormancy under the influence of CH mutations in HSCs 3) Last, we aim to translate our findings to human CH in patients, by studying differentiation trajectories in patients carrying CH mutations in splicing factor and epigenetic regulator genes, and want to find aberrant surface marker profiles of CH-mutated stem/progenitor cells for advanced detection of CH. This project will enlighten the molecular and functional mechanisms of clonal dominance caused by important CH driver genes and how the interplay between intrinsic and extrinsic factors shapes clonal development over time.