Abstract
lorectal cancer (CRC) is the third most diagnosed cancer and second most deadly in the
world. This project deals with characterization of mononuclear phagocyte system (MPS) cells in
circulating blood of patients with CRC. This is a pilot study to determine if differences are detected in
MPS cells in CRC with the aim of biomarker discovery. There has been an exciting and growing focus
in CRC research to identify novel biomarkers and pathogenic mechanisms, especially for detection and
treatment of early CRC. CRC incidence has been steadily rising worldwide. There have been great
advances in diagnostic and therapeutic methods towards detecting early CRC that is often
symptomless. Despite this, CRC is still commonly diagnosed in an advanced stage. Currently a
non-specific stool test called Faecal Immunochemical Test (FIT) is used in CRC screening. In addition to FIT
being poorly selective, there is also poor patient uptake of this stool based screening test. A blood test
that detects CRC is more acceptable for much of the population adding to the rationale for this
research focus.
Cells from the MPS have emerged as important regulators of cancer development and progression.
The MPS comprises monocytes, macrophages, and dendritic cells. Lineage determining cytokines such
as colony stimulating factor 1 (CSF1), CSF2 and CSF3 drive the development and differentiation of MPS
cells. Blood monocytes are regarded as precursor cells of the MPS; when recruited into the tumour
microenvironment they differentiate into tumour-associated macrophages (TAMs). TAMs are a critical
component of tumour microenvironment affecting tumour growth, tumour angiogenesis, immune
regulation and metastasis. Monocytes represent a window between haematopoiesis in bone marrow
and recruitment to tissues as TAMs. I have capitalized on this window to investigate if MPS immune
cell changes can be used as proxy of CRC detection and explore cancer therapy targets. Single receptor
cytokine inhibition in cancer therapy has not yielded positive results, therefore a greater
understanding of what is happening with macrophage receptors in tissues and blood as monocytes is
required.
I have used fluorescence-activated cell sorting (FACS) with a multicolour panel of antibodies to enable
the study of the MPS in blood with new combinations of markers including CSF1R, CSF2R and CSF3R.
There are currently no studies measuring expression of CSF1R, 2R or 3R in blood in cancer. In the study
of other cancers, higher expression of CSF1R in tumour tissue is associated with worse survival. I have
studied CRC tissue with these markers to evaluate if there is correlation between MPS cells in blood
and the tumour immune infiltrate in patients with CRC. My results show that CSF1R captures all
mononuclear cells subsets described till now. Although evaluating MPS cells based on numbers and
expression of CSF1R, CSF2R and CSF3R did not differentiate between CRC and related pathologies,
interesting changes in CSF1R positive cells were observed during this study, suggesting
reprogramming of these cells during malignancy. In patients with CRC, there is a significant reduction
in a subset of dendritic cells with inflammatory function called DC3 (mean DC3 absolute cell count in
CRC 3805 cells/mL, control 9564 cells/mL, p=≤0.01 and DC3 mean percentage of total CSF1R cells in
CRC 1.15%, control 2.60%, p=≤0.01). DC3 dendritic cells are a recently defined subset and requires
ongoing investigation to understand DC3 role in CRC. Studying CRC tissue has shown higher CSF1R
expression at the tumour invasive front than the intratumoral region. There also appears that there is
a positive correlation with higher CSF1R expression in tissue in the intratumoral region with higher
circulating expression of CSF1R.
Although this study has not found a clinically relevant biomarker for diagnosing CRC, it has helped in
the understanding of the origin and fates of monocytes, and related family members such as dendritic
cells. Continued research in this area will establish a clearer picture of all MPS cells in CRC and provide
better understanding of the immunopathology leading to CRC