Characterisation of the Immune Landscape in Multiple Myeloma

Multiple myeloma (MM), a haematological malignancy, is characterised by a clonal proliferation of plasma cells in the bone marrow (BM). Incidence rates have been increasing since 1994. Whilst 5-year survival rates have also increased, MM remains an incurable frequently relapsing disease. The development, progression and resistance to therapy in MM are intricately connected to the heterogeneous tumour microenvironment (TME), the BM. Immune cells in the MM BM are highly altered. Hypothesising that dysfunction arises in the major cytotoxic cells present in MM BM, alongside an alteration of suppressive subsets, this thesis performed a deep characterisation of the major lymphocytes of the TME. Using a combination of flow cytometry immunophenotyping, single-cell RNA sequencing (scRNA-seq) and functional analysis of MM patient samples, we elucidate the cellular factors associated with MM. We reported increased frequencies of immune subsets in MM including CD57+ T cells and CD56-CD16+ NK cells that may be relevant targets for novel therapeutic strategies. Functional studies demonstrated a reduced response to stimulus in both the T and NK cells. To understand the immune suppressive mechanisms, we characterised the frequency and phenotype of regulatory cells. Decreased frequencies of myeloid suppressor cell subsets were found, and deep immunophenotyping of T regulatory cells found a highly suppressive phenotype. High heterogeneity was observed in the MM plasma cells. We characterised the changing immune cell landscape in daratumumab treatment using a combination of transcriptional and functional studies, and we reported increased cell subsets and a shift towards T cell effector memory post-daratumumab treatment. We also demonstrated the use of intracellular epitope labelling in combination with surface AbSeq in a scRNA-seq. This research addressed the gap in the BD Rhapsody technology by demonstrating the successful use of this assay to identify key cell subsets. The work in this thesis improves our understanding of the immune landscape in MM and may inform the future development of cellular therapies.