Abstract
Atherosclerosis is a leading cause of mortality worldwide. It is characterised by a slow- progressing inflammation, which results in the deposition and accumulation of lipids beneath the endothelium. Macrophages engulf deposited lipids, forming foam cells that accumulate and die, resulting in the formation a plaque. Regulatory T cells (Tregs) are suppressive CD4+ lymphocytes that have been reported to be atheroprotective. Both decreased Treg frequency and impaired functionality is associated with disease progression, the cause(s) of these Treg aberrations remains to be elucidated.Atherosclerosis is a complex multifactorial disease. As such, I sought to characterise the influence of hyperlipidaemia, a key risk factor for atherosclerosis, on immune components of patients with a particular focus on Tregs. Subsequently, I sought to determine the ability of healthy Tregs to limit disease progression through interactions with macrophages in the presence of oxLDL. We and others have previously reported Tregs to influence macrophage phenotype and function. Whether this phenomenon persists in the presence of atherosclerotic associated factors is unknown. Currently, there is no curative therapy for atherosclerosis. Instead, patients rely on surgical intervention and pharmacological management of risk factors, neither of which act to resolve the underlying inflammatory microenvironment. As Treg therapy is showing promise in other fields, I investigated the possibility of utilising Tregs as a novel cellular therapeutic for the treatment of atherosclerosis.
Extensive phenotyping of B cells, Tregs, monocytes, and cytokines in the peripheral blood of both patients with hyperlipidaemia and corresponding healthy controls was undertaken using multi-parameter flow cytometry and formed part of the study ‘Investigation of Immune Regulation and Cellular Response in patients with dyslipidaemia’ (IRAS number 236524). Findings from this study supported and extended upon previous publications, indicating modulation in both the cellular compartment and cytokine milieu of patients toward that of a more inflammatory disease-permissive state. Of note, increased expression of both CCR4 and CD95 on Treg population(s) was observed in hyperlipidaemic patients. Such finding may allude to an increased predisposition of these Tregs to Fas-induced apoptosis in patients.
A ex vivo cellular co-culture system was established for the investigation of macrophages and Treg interactions in the presence or absence of oxLDL, a key component of the atherosclerotic microenvironment. Significantly, this study reports for the first time, a novel atheroprotective mechanism of human Tregs whereby Tregs ameliorate detrimental ‘inflammatory’ phenotypic changes ‘M2’-like macrophages resulting from their interactions with oxLDL as indicated by altered expression of markers including CD86, CD16 and CCR4. This was further accompanied by functional modulation, which results in the decreased accumulation of oxLDL in macrophages.
Finally, preliminary data utilising atherosclerosis-associated peptide antigens suggests the presence of both regulatory and effector antigen specific CD4+ cellular population(s) exist in the circulation of both healthy individuals and hyperlipidaemic patients. In healthy individuals, antigen specific CD4+ cells were predominantly Tregs and suggest that antigen specific Tregs may limit disease onset and progression. Should this be the case the generation of atherosclerosis-associated antigen specific Tregs may offer a novel cellular therapeutic option for the treatment of atherosclerosis.
Findings presented in this thesis encourage the continued investigation of Tregs as a novel therapeutic for the treatment of human atherosclerotic disease. Evidence would suggest that both the exogenous expansion of atherosclerosis associated antigen specific Tregs for adoptive cellular therapy and the induction of an endogenous atheroprotective Treg population by way of a tolerogenic vaccine are viable avenues which warrant further examination.
| Date of Award | 1 Jul 2021 |
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| Original language | English |
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| Supervisor | Giovanna Lombardi (Supervisor) & Cristiano Scotta (Supervisor) |