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Title: Expression of factors within tumours to reduce immune suppression
Author: Jakeman, Philip G.
ISNI:       0000 0004 6497 8251
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2015
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Macrophages are important immune cells that play central roles in both health and disease. They display a broad phenotypic diversity, although for simplicity two distinct subtypes have been denoted '1' and '2'. While this nomenclature is overly simple, it does provide a useful framework for classifying different macrophages. M1 macrophages are largely characterised by their pro-inflammatory, disease-fighting functions, whereas M2 macrophages are involved in wound healing, tissue remodelling and immune suppression. Macrophages are often present at high numbers within solid tumours, and although this was historically expected to correlate with a good prognosis, in fact, most 'tumour-associated macrophages' (TAMs) are more M2-like and can support tumour development and growth. This thesis aims to assess the plasticity of TAMs and to determine whether and how TAMs might be 're-educated' to become more M1-like, potentially thereby switching from their tumour-supporting role to a tumour-killing function. The overarching purpose is to develop an oncolytic adenovirus capable of killing tumour cells but genetically 'armed' to express biological mediators locally to re-educate TAMs and activate their tumour-killing activities. A variety of human and murine macrophages were studied in this thesis, including cell lines and primary cells from malignant ascites. Macrophage polarisation was measured, and the potential for re-education from M2 to M1 was assessed using gamma interferon (IFN-γ) with and without lipopolysaccharide (LPS). Morphological (e.g. Major histocompatibility complex (MHC) class II expression) and functional re-education (e.g. production of nitric oxide, NO) were both achieved using IFN-γ alone, although this was more effective when the original M2-polarising environment was removed. Interestingly only M1-polarised macrophages showed the ability to cross present antigens, both as free peptides and as tumour-associated proteins. An oncolytic group B adenovirus was synthesised, based on ColoAd1, expressing IFN-γ (murine and human versions for different applications) and the effect of exposing macrophages to virus particles or to the lysates of virus-infected cancer cells was explored. Virus alone showed an intriguing ability to functionally re-educate M2 macrophages, assessed by NO production, although this was dramatically enhanced when it encoded IFN-γ. The IFN-γ-expressing virus also showed greater re-education activity than free IFN-γ, probably reflecting the short in vitro half-life of IFN-γ when given as a free cytokine, which can be overcome by continual production from virus-infected tumour cells. This might be coupled with the intrinsic ability of the virus to stimulate pro-inflammatory macrophage responses. Overall this thesis shows a high level of plasticity between macrophage subtypes, and a clear potential for re-education of M2 macrophages to a more pro-inflammatory phenotype using genetically modified oncolytic viruses.
Supervisor: Seymour, Leonard ; Fisher, Kerry ; Jiang, Shisong Sponsor: Medical Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available