Defining malignant hematopoiesis via single-cell multi-omics

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PROJECT SUMMARY / ABSTRACT Clonal blood differentiation through the acquisition of somatic mutations result in abnormal accumulation of blood components and clinically manifest as myeloid disorders. The study of how these somatic mutations perturb the differentiation trajectories in human hematopoiesis is often challenged by the admixture of normal hematopoietic cells with the neoplastic cells that cannot be distinguished by cell surface markers. To overcome this limitation, we developed a novel single-cell multi-omics Genotyping of Transcriptomes (GoT) platform that directly links somatic genotypes with transcriptomes of thousands of single cells. Thus, GoT enabled the comparison of mutant and wildtype cells within the same sample in the context of progenitor identities, thereby turning the co-mingling of mutant and wildtype hematopoiesis from a limitation to an advantage. As proof of principle, GoT was applied to CD34+ progenitor cells from patients with calreticulin- mutated myeloproliferative neoplasms (MPN), revealing key pathways that were aberrantly activated in the mutant cells, such as a robust unfolded protein response in the megakaryocytic progenitors, on the one way, and NF-KB pathway in stem cell-enriched populations, on the other. Overall, GoT revealed that the transcriptional impact of calreticulin mutations is highly variable as a function of progenitor identity – which bears significant implications for therapy by enabling the discovery of targetable pathways specific to the earliest stem cells. Thus, to demonstrate the cell identity-dependency across other key driver mutations, as a fundamental concept in myeloid disorders, I will apply GoT to thrombopoietin receptor-mutated progenitor cells and to clonally-diverse cells from MPN samples (Aim 1). Next, in order to define cell extrinsic determinants of somatic mutation impact, I will determine the immune niche interactions with calreticulin-mutant and wildtype progenitor cells, as well as the impact of immunomodulatory therapy on these interactions (Aim 2). Finally, I will test the hypothesis that the cell’s epigenome precedes the cell identity-dependency of somatic mutation effects, by developing and applying a novel single-cell platform that integrates somatic genotyping with chromatin accessibility states of progenitor cells (Aim 3). Thus, I will define the genetic, epigenetic, transcriptional and environmental factors that culminate in the clinical output of somatic mutations in human hematopoiesis. These studies will, therefore, unveil not only fundamental concepts in clonal hematopoietic differentiation but also specific targets for therapeutic intervention.