Abstract:
This thesis aimed to better understand the current hurdles preventing more effective
cancer treatment. This was investigated from two angles, cancer stem cells (CSCs)
and tumour immunity.
CSCs possess the capacity of self-renewal and the ability to give rise to progeny with
the potential to proliferate and differentiate. As such, these cells are able to
differentiate into different lineages and clones that make up the tumour mass and as
such are claimed to represent a major form of resistance to conventional therapeutic
approaches which must be overcome in order to achieve better cancer treatments. In
melanoma, the identification and characterization of CSCs remains incomplete, with
many studies reporting conflicting findings. To bridge this gap in understanding, the
expression of markers which identify CSCs in melanoma on a putative basis
(ALDH1A1, ABCG2, CD44v7/8, CD44v10, CD133, CD271 and Nestin) was studied
in vitro in cell lines, in situ in tissues and in healthy control samples. It was observed
that CSC markers were expressed by the majority of melanoma cells in vitro and in
situ, but they were also found on healthy differentiated tissues and cells, indicating
that they are not specific markers for cancer stem cells. Furthermore, the clinical role
of selected CSC markers was investigated in melanoma tissues, revealing that high
levels of ABCG2 were associated with advanced clinical stage, while higher
expression of both ABCG2 and CD133 correlated with poorer patient survival. These
data pave the way for the validation of these moieties as therapeutic targets for
melanoma in future.
Despite the recent expansion in the use of immunotherapy for many cancer types, it
is still not a standard treatment for breast cancer. To assist in the clinical
implementation of immunotherapy in breast cancer, this investigation sought to
characterise the immune systems of breast cancer patients with the aim of identifying
therapeutic targets and prognostic indicators in the following settings 1) patients
compared to healthy women, and 2) under treatment with different forms of therapy.
To do this, the frequencies of myeloid and lymphoid immune cells at different stages
of differentiation were investigated in the peripheral blood of breast cancer patients
using multiparametric flow cytometry. Functional in vitro assays were additionally
employed to investigate mechanisms of immune function. The results revealed that
4
compared with healthy women of the same age, breast cancer patients have
significantly elevated frequencies of cells with a myeloid-derived suppressor cell
phenotype in the blood as well as higher levels of T cells at earlier stages of
differentiation. Furthermore, functional testing showed that myeloid cells from breast
cancer patients more potently suppressed autologous T cell proliferation than cells
from healthy women, which was found to be partly mediated by the release of
reactive oxygen species. The peripheral immune system was then investigated for
association with breast cancer prognosis in patients under different therapeutic
settings. This study found that the levels of circulating T cells in patients treated with
high-dose paclitaxel-containing therapy correlated with patient survival. By contrast,
patients treated with high-dose cyclophosphamide-containing therapy showed no
such associations. Correlations with the level of circulating myeloid cells were also
found. Considering these results for peripheral blood, T cells and myeloid cells were
then investigated in the tumour mass for their relevance to patient outcome. The
results of this study showed that patients with higher levels of intra-tumoural T cells
were clinically fitter and experienced longer breast cancer-specific survival. In
contrast, high relative levels of granulocytic cells were found in patients with poorer
clinical health. Collectively, the results of these studies show that immune alterations
in the blood and tumours of breast cancer patients may be used to gain insight into
new prognostic biomarkers that could assist in developing new immunotherapies for
this disease.
Print-on-Demand