Characterisation of the immune cell content of bone marrow from patients with multiple myeloma

Abstract

Multiple myeloma(MM) remains an incurable cancer responsible for 2% of cancer deaths. Immune dysfunction is described in MM, with roles ascribed to regulatory T cells(Tregs), and co-inhibitory receptors such as PD-1 and LAG-3, providing the rationale for immunotherapies to restore T cell function. Hypothesising that defects in T cell immunity are evident at diagnosis and post autologous stem cells transplant(ASCT), and predictive of clinical outcomes, this thesis undertook detailed characterisation of T cell subsets from the bone marrow(BM) of newly diagnosed(ND) and post-ASCT patients by flow cytometry, and correlated with progression free survival(PFS). Additionally, a CyTOF panel was validated to be used for BM samples from MM patients. The ultimate aim is to understand immune suppressive factors in the BM microenvironment. This work identified Tregs and frequency of PD-1 on CD4 effectors to be associated with shorter PFS in ND patients. Analysis of T cell subsets revealed that low CD4 effector:Treg ratio, and increased frequency of PD-1 on CD4 effectors(CD4effPD-1hi) were independent predictors of relapse in addition to conventional risk factors. Patients with CD4effPD-1hi displayed transcriptional and functional features of T cell dysfunction which may contribute to poor clinical outcomes. These findings support the possible use of Tregs and PD-1 on CD4 effectors as biomarkers of risk and as potential targets for immunotherapeutic strategies. In post-ASCT patients, a high frequency of PD-1 on CD4 effectors, Ki-67 on CD8 T cells, and high frequency of LAG-3 on CD4 effectors, CD8, and Tregs correlated with shorter PFS. This study identified a subset of patients with T cell phenotype indicative of exhaustion to have shorter PFS and prompt further functional studies to uncover immune drivers of disease progression post-ASCT. This work improves our understanding of immune suppressive factors in MM, which may help inform immunotherapeutic strategies in these patients.