title: The role of adaptive and innate immune cells in patients with colorectal cancer
Creators: name: Inthagard, Jitwadee
Publisher: name: University of Glasgow
Year: 2022

description: The aim of this study was to fully understand the differing immune landscapes within colorectal cancer (CRC) patients’ tumours, how these affected histological subtypes and response to immunotherapy as well as assessing their underlying genetic backgrounds. The first part assessed IHC staining for the full patient cohort to obtain baseline results of the association between immune cells infiltration and patients’ survival. Then immune landscapes were developed from a combination of T-lymphocytes and myeloid cells to mimic different immune statuses within the tumour. The results found that high level of T-lymphocytes infiltration was associated with improved patients’ survival independent of myeloid cells infiltration within both tumour cell nests and tumour stroma. Whereas high level of myeloid cells infiltration was associated with decreased patient’s survival only when T-lymphocytes where low. The association between immune cells infiltration and CRC phenotypic subtyping was then assessed to understand if there is a different immune cell composition specific to each phenotypic subtype which could be used as prognostic biomarkers or as targets for immunotherapy. This showed that each subtype had a separate immune landscape, with the immune subtype being associated with lymphoid cells, and the stromal subtype with myeloid cells. The second part involved genomics and transcriptomics analysis to obtain potentially mutated and differentially expressed genes specific to each immune landscape which might be used as biomarkers. The genomics analysis showed that TP53 mutation was the most significantly mutated gene which showed a high mutation frequency in patients with high myeloid cells in their tumour stroma, especially when combined with high levels of CD80+ M1-like macrophages. In addition, at the protein level, p53 protein expression showed significant correlation with TP53 mutations, and high TP53 mutations were associated with high p53 expression, which significantly improved patients’ survival. As TP53 mutation showed a higher frequency in patients with high levels of CD80+ M1-like macrophages infiltration within their tumour stroma, TP53 mutations and its effects on p53 expression might be one of the factors to influence myeloid cells infiltration into stroma. Similarly, transcriptomics analysis found different pattern of gene expressions for each immune landscape. The results suggested that expression of significantly differentially expressed genes might be influenced by high myeloid cell infiltration independent of which other cell types are present in the tumour microenvironment. The most significantly differentially expressed genes were again linked to the TP53 network at a protein-protein interaction level, further strengthening the link between the TP53 network and immune response in CRC. Interestingly, when assessing the correlation between TP53 mutation and differentially expressed genes, it was found that the REGs gene family, REG1A, REG3A, and REG3G, were downregulated in patients with TP53 mutations. As REGs genes are proposed to play a role in promoting colon tissues tumorigenesis this would fit with previous research. However, one limitation of this study was its small sample size. Therefore, validation in a larger cohort is needed to confirm these findings. The final part was to assess the efficacy of three anti-PD-1/anti-PD-L1 checkpoint inhibitors individually and in combination on a 3-D CRC tumour spheroids model co-cultured with different immune cell types. This model was designed to co-culture CRC tumour spheroids with non-adherent lymphocytes and macrophages, either individually or in combination. The model was developed by assessing the optimum cell density, media, and inhibitor concentrations. However, the result showed no difference in tumour spheroid viability for any immune checkpoint inhibitor at either 48 or 96 hours for any of the co-culture combinations. This suggests that further optimisation of the model is needed to be a useful tool for immunotherapy research. In conclusion, the results show that differing immune landscapes can stratify CRC patient prognosis. Furthermore, these immune landscapes vary between histological phenotypic subtypes and are linked to mutant p53 expression. With further research, these immune landscapes may be a useful tool to assess and stratify patients for treatment with immunotherapy.