Investigation of unconventional T cells in patients with haematological malignancies

Abstract

Haematological malignancies involve the uncontrolled division of white blood cells, which can lead to an accumulation of these cells in lymphoid organs and cause the disruption of normal immune function. Multiple Myeloma (MM) and Myelodysplastic syndromes (MDS) are the most common haematological disorders among the elderly (Elidrissi Errahhali et al, 2016), but despite recent advances in treatment options, most individuals with MM or MDS eventually relapse and succumb to the disease (Rjkumar 2020 and Schurch 2018 and Kumar et al, 2012). The association of immune defects with MM and MDS may be a factor in disease progression, therefore it is important to develop a comprehensive understanding of how the immune system changes throughout the progression of these diseases, so that more effective treatment options can be developed. This thesis presents a detailed analysis of the frequency, phenotype and function of conventional T cells, unconventional T cells and antigen presenting cells (APC) throughout the progression of MM and MDS. This analysis has identified a range of immune abnormalities within these patient groups, including novel findings that provide new insights into disease progression and potential new targets for immune therapies. Some of the abnormalities we identified in patients with MM and MDS include; a reduction in the frequency of unconventional T cell (Natural Killer T (NKT) cells and Mucosal Associated Invariant T (MAIT) cells), as well as reduced frequencies of various APC populations. We also reported an increased expression of chronic activation and exhaustion markers on CD8+ T cells and MAIT cells, despite their retention of functional capacity. Importantly, the abnormalities we observed in patients with MM were consistent from the pre-malignant disease stage to active disease, which has not been shown previously suggesting that many of these defects are present from very early in disease development. We also identified key differences in the frequency and phenotype of conventional T cells, unconventional T cells and APC between patients with MM and those with MDS. Together highlighting the many different immune changes that are occurring within these patients groups and the importance of analysing haematological malignancies as individual diseases rather than as a collective. One of the most significant findings in this thesis was the alteration in frequency and phenotype of MAIT cells within the blood of patients with MM and MDS. MAIT cells may have important roles in anti-tumour immunity, so we explored the potential causes of these changes, including soluble factors and cell-to-cell interactions between MAIT cells and APC. Interestingly, we found MM patient plasma contained increased levels of IL-18, which is a cytokine known to influence MAIT cell function. This led us to establishing a long term in vitro culture of sorted MAIT cells supplemented with IL-18, finding that culturing MAIT cells with IL-18 lead to rapid expansion of MAIT cells without otherwise alternating their phenotype or function. We next established a novel mixed-donor MAIT cell co-culture system to examine the interactions between sorted healthy MAIT cells and APC from patients. This system uniquely allowed us to investigate whether abnormal patient APC were capable of stimulating MAIT cells and whether MAIT cell responses were altered as a result of this interaction. Whilst this was conducted as a pilot study to look for potentially important interactions rather than significance, we did conclude that culturing healthy donor MAIT cells with APC from monoclonal gammopathy of undetermined significance (MGUS) and MM patients did not lead to alterations in phenotype. The development and application of these long term MAIT cell cultures shed new light on how MAIT cell defects emerge in MM and MDS, and has also provided valuable insights into optimal MAIT cell growth conditions, which could be applied in the future to analyse other complex disease settings and for the use in therapeutic approaches. Our research was the first comprehensive study to characterise immune system alterations at both the individual cell population level and to examine their functional interactions throughout all stages of MM and in MDS. We discovered a range of novel findings which have greatly improved our understanding of the role that these various immune cells populations might play in MM and MDS, and identified new areas of study that could lead to improved disease management.Doctor of Philosoph