The role of AML secretome and bone marrow microenvironment in establishment and maintenance of leukaemia initiating cells

Thesis

Acute myeloid leukaemia (AML) is the most common acute leukaemia in adults and is characterised by the accumulation of immature malignant precursors in haematopoietic and other tissues. Even though next-generation sequencing has dramatically advanced our understanding of the genomic landscape of AML and identified many leukaemia-associated gene signatures, intensive chemotherapy remains the mainstay of the general therapeutic strategy without much progression over decades. In addition, AML still has the worst overall survival among adult haematological malignancies. The prognosis and survival for elderly patients who are too frail to be eligible for intensive chemotherapy can be even poorer. Therefore, the identification of novel AML dependencies is urgently needed to develop less toxic therapeutic strategies that can potentially eliminate AML cells, especially the self-renewing leukaemia initiating cells (LICs).

One potential therapeutic target could be the cell surface receptors on LICs, which covey autocrine and paracrine signals existing in the bone marrow (BM) microenvironment, as there is considerable evidence that de-regulated BM microenvironmental factors could contribute to AML development. In order to identify cell surface receptors essential for LIC maintenance, I performed in vivo CRISPR-based screens focused on the cytokine and chemokine receptor genes in the context of a murine model of bi-allelic CEBPA mutant AML. This murine AML model, as opposed to the commonly used MLL-AF9 model, is strictly BM microenvironment-dependent, which allows better characterisation of the interplay between LICs and the microenvironmental factors. By doing this, I identified and successfully validated 2 cytokine receptor genes, Ccr1 and Il7r, as in vivo AML dependencies. Of note, these 2 genes are highly overexpressed across different subtypes of human AML cells, indicating their potential use as therapeutic targets for patients with AML.

Besides, in light of previous evidence suggesting the aged BM microenvironment’s implication in AML propagation, I sought to investigate further the biological basis for the aged BM microenvironment’s ability to facilitate AML progression. Several inflammation-related process networks were simultaneously enriched in BM stromal cells during ageing and AML development. In particular, I demonstrated that both physiological ageing and CEBPA mutant AML progression induced elevated protein levels of the pro-inflammatory CCR1 ligands, CCL3 and CCL5, in the BM cavity. This implied the role of CCR1 signalling as an ageing-associated AML dependency. Indeed, expansion of the murine Cebpa mutant AML cells in the unperturbed aged BM was significantly impaired by a selective CCR1 inhibitor. This suggests that physiological ageing harnessed CCR1 ligands as a critical mediator in age-associated AML predisposition, and targeting CCR1 can potentially benefit elderly patients with AML.

Authors: Ren, X

• DOI: 10.5287/ora-7jrvmk6pp
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: AML; microenvironment; cytokine receptor; leukaemia initiating cells