부산대학교 도서관

Immune checkpoint blockade has provided a revolution in solid cancer treatment particularly in the metastatic setting. Although many patients demonstrate clinical responses upon receiving checkpoint therapy, a considerable number of individuals fail to benefit from treatment and continue to progress from their cancers. It is therefore important to establish the immunological contributors that mediate treatment success and identify easily accessible biomarkers that can be used to monitor this process. Here, I utilised bulk and single-cell RNA sequencing, and flow cytometry, to characterise early peripheral immunity across immune checkpoint blockade in an Oxford-based cohort of metastatic melanoma patients. Firstly, I focus on peripheral CD8+ T cells as central mediators of anti-tumour responses. I demonstrate that a central tenet of the immune response to immune checkpoint blockade is mitosis, which is accompanied by type I interferon and interferon-G signalling and other immune activation pathways. I then employ single-cell RNA sequencing to dissect the CD8+ T cell compartment, finding that mitotically active cells are under-represented amongst clonal expansion. Instead, cytotoxic effector cells and expanding effector memory cells dominate the clonal pool and demonstrate phenotypic and clonal stability across immune checkpoint treatment. Immune checkpoint blockade shifts T cell subsets towards increased differentiation and has particularly stimulatory effects on effector CD8+ T cells. Next, I describe how these aspects of peripheral CD8+ immunity contribute to clinical patient responses and survival. Individuals with greater levels of CD8 clonal expansion and effector responses show improved treatment outcomes, whilst mitosis and interferon activity have limited patient benefit. I describe how a simple, tractable measure of clinical lymphocyte count predicts long-term survival benefit for patients. Lastly, I dissect how CD8+ T cell responses interact with other immune subsets, such as monocytes, B cells and CD4+ T cells to create expression and subset composition networks that reflect enhanced T cell activity and homeostasis, or dysregulated inflammation and suppressed T cell immunity. Intersecting these responses with genetic variation provides further insight into the factors influencing immunotherapy responses. Altogether, these results generate multiple blood-based biomarkers to predict therapy success, and provide novel angles for therapeutic adjuvants to support immune checkpoint blockade, spanning potential cellular, cytokine and metabolic mechanisms.