Epigenetic contributions to cancer immunosurveillance
File(s)
Author(s)
Lee, Puay Ling
Type
Thesis
Abstract
Immunosurveillance is a critical protective mechanism against tumour formation. As cancer cells evolve due to intrinsic genomic and epigenomic instability, and immune selective pressure, they may acquire immunoediting traits to avoid killing by the immune system. Although loss-of-function mutations in epigenetic regulators, which control gene expression, are a recurrent phenomenon in multiple human cancers, there has been little work to date exploring how these mutations enable cancer cells to evade immunosurveillance.
This thesis aims to investigate the epigenetic basis of cellular transition from an immunogenic to an immunoevasive state. To begin, I derived a cancer cell line (RagL1) that developed spontaneously in an aged Rag2-/- immunodeficient mouse. RagL1 cells were rejected by the host when transplanted into syngeneic immunocompetent mice, indicating an immunogenic phenotype. Using an in vivo CRISPR/Cas9 pooled screen to knockout 539 epigenetic regulators in RagL1 cells, I identified Pcgf1, a member of the polycomb repressive complex family, as a candidate target. Transcriptional profiling of Pcgf1 KO cells revealed a strong suppression of IFNg and IFNa signalling response pathway genes, including IFN signal transduction proteins, antigen processing and presentation molecules, immunoproteasomes, and chemokines. There was also upregulation of transcriptional repressors and immune checkpoint protein expression. In addition, in vivo subcutaneous transplantation of Pcgf1 KO cells into flanks of mice revealed the formation of progressive tumours which were infiltrated by lymphocytes that
were less activated and cytolytic.
Overall, the findings propose a model whereby loss of PCGF1-mediated epigenetic control may enable cancer cells to avoid recognition by immune cells and inhibit activation of immune effector cells, although the direct cancer-immune cell interactions remain to be formally demonstrated.
This thesis aims to investigate the epigenetic basis of cellular transition from an immunogenic to an immunoevasive state. To begin, I derived a cancer cell line (RagL1) that developed spontaneously in an aged Rag2-/- immunodeficient mouse. RagL1 cells were rejected by the host when transplanted into syngeneic immunocompetent mice, indicating an immunogenic phenotype. Using an in vivo CRISPR/Cas9 pooled screen to knockout 539 epigenetic regulators in RagL1 cells, I identified Pcgf1, a member of the polycomb repressive complex family, as a candidate target. Transcriptional profiling of Pcgf1 KO cells revealed a strong suppression of IFNg and IFNa signalling response pathway genes, including IFN signal transduction proteins, antigen processing and presentation molecules, immunoproteasomes, and chemokines. There was also upregulation of transcriptional repressors and immune checkpoint protein expression. In addition, in vivo subcutaneous transplantation of Pcgf1 KO cells into flanks of mice revealed the formation of progressive tumours which were infiltrated by lymphocytes that
were less activated and cytolytic.
Overall, the findings propose a model whereby loss of PCGF1-mediated epigenetic control may enable cancer cells to avoid recognition by immune cells and inhibit activation of immune effector cells, although the direct cancer-immune cell interactions remain to be formally demonstrated.
Version
Open Access
Date Issued
2022-08-25
Date Awarded
01/03/2023
License URL
Advisor
Hayday, Adrian
Sponsor
Agency for Science, Technology and Research Singapore
Publisher Department
Department of Surgery & Cancer
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)