Immunometabolism in tolerance and inflammation: insights from checkpoint inhibitor therapy for solid tumours

Checkpoint inhibitors (CPIs) are a class of drug which reduce the regulatory effects of immune checkpoints, mainly targeting PD-1, CTLA-4, and more recently LAG-3. Tumours often upregulate the ligands of these checkpoints, dampening the immune response and preventing tumour clearance. CPIs are therefore used in anti-cancer treatment to support anti-tumour T-cell effector responses. While CPIs have been used in the clinic for over 10 years and have been transformational in cancer treatment, many patients experience immune-related adverse effects, such as skin rashes and colitis, which can impede treatment and even be life-threatening (1). Previous work in this area demonstrated little difference between activated human PBMCs treated with CPIs or left untreated in vitro, which does not align with the clinical effect of these drugs. This project seeks to build on this previous work by developing an in vitro model of CPI treatment in peripheral T-cells that incorporates exhaustion, to better replicate the conditions experienced by T-cells in cancer patients in vivo. In this model, the phenotypic changes occurring in T-cells after CPI exposure will be studied, with the aim of identifying a predictive marker of CPI toxicity. In addition, previous work from the lab revealed that patients who develop severe toxicities have an increased naive:effector ratio of CD4+ and CD8+ T cells at baseline (before start of CPI treatment), highlighting that patients' characteristics could be a determinant of future toxicities (2). We hypothesise that this shift in immune composition may be due to increased migration of cells into tissue, expanding populations of tissue-resident memory cells (TRM) in those developing severe organ toxicities, and that TRM may play a critical role in both CPI efficacy and development of toxicity. TRM can be challenging to work with, due to their low numbers in peripheral blood and the difficulty of accessing human tissue samples. This project aims to create an in vitro model of TRM by drawing on several models identified in the literature, enabling examination of the impact of CPI treatment on TRM phenotype and effector function. Finally, it has been discovered by the host laboratory that blocking the cholesterol biosynthesis pathway prevents CD4+ T-cells from switching from effector-like to regulatory-like, thereby preventing resolution of the immune response, and enhancing/prolonging effector responses (3). This project intends to test this effect in the exhaustion and TRM in vitro models developed to assess whether cholesterol blockade could be used as an adjuvant to CPI treatment, increasing the duration and effectiveness of the subsequent anti-tumour response. Together, these three strands will contribute to a greater understanding of the mechanisms of CPI treatment and their effect on specific T-cell subsets. This will pave the way for better predictions of toxicity development for patients, and potentially options to improve the efficacy of treatment, leading to better outcomes for patients.