Glioblastoma Multiforme (GBM) is a primary malignant brain cancer, affecting children and adults and has a very poor prognosis. Up to 30% of the tumour mass consists of host derived immune cells, and a better understanding of how these cells affect tumour behaviour is required. These cells, called 'Tumour Associated Macrophages' (TAM) have been shown to occur in peripheral solid organ cancers, where they can cause local immune suppression, increase invasiveness and aid tumour growth. In the brain however, TAMs can consist of centrally derived microglia and peripherally derived macrophages, and although these cells could be exerting different effects on the tumour, there is currently no reliable way of distinguishing between the two. Cancer Stem Cells (CSC) are a subpopulation of cells within the tumour mass with stem-like features, are capable of self-renewal, and can recapitulate a tumour in an immunocompromised mouse host. It is thought that these cells play a role in disease recurrence and hence represent a potential target for anti-GBM therapies.In the first project we investigate the interaction between Cancer Stem Cells and TAMs. We first describe a method of culturing CSCs and TAMs from a single human patient sample, followed by an investigation into the functional properties of these cell types. We found functional differences between established cell line pairings of U87-MG and CHME3 versus primary patient derived CSCs and TAM cell line pairings. Polarisation of microglia/TAMs with lipopolysaccharide caused significant decrease in proliferative capacity of the GBM cell lines.Next we used a Non-Myeloablative Conditioning System (NMCS) to selectively replace the peripheral bone marrow compartment of wild type animals with labelled bone marrow cells, without disturbing brain homeostasis. We demonstrate that peripheral cells home exclusively to the orthotopically implanted tumour, and that some of these cells are CD11b+ and Gr1+, suggestive of myeloid derived suppressor cells (MDSC). We evaluate current CD45 based gating strategies for distinguishing peripheral and central cells and show them to be inadequate.Finally we compared the chemosensitivity profiles of different patient derived CSC lines using high throughput content screening (HTCS), against currently approved chemotherapeutic drugs and rank these drugs in a response space, based on HTCS parameters including 2D and 3D culture with and without irradiation. Differential chemosensitivities were noted between different patient derived cell lines. Drugs not currently used in the treatment of GBM such as Actinomycin D and Mitoxantrone were also identified using HTCS, suggesting the potential utility of such an approach to personalised treatments in GBM.