This project has been conducted on different fronts, which are structured into three research thrusts.
First, Mitophagy-guided T cell anti-tumor immunity, we investigate the contribution of damage mitochondria removal machinery (mitophagy) on supporting T cell anti-tumor immunity. In this part, we confirm that a) mitophagy is required to support T cell anti-tumor immunity, maintain responsiveness to PD-1 blockade, drive formation of stem-like tutor-specific TILs; b) chronic T cell receptor stimulation and hypoxia in tumors abolish mitophagy activity in T cells; c) TILs accumulating depolarised mitochondria as a result of impaired mitophagy commit to terminally exhausted program. This exhausted features are characterised by functional, transcriptomic and epigenetic features, including changes in DNA methylation and chromatin accessibility.
Second, mitochondria-nucleus communication on guiding T cell anti-tumor responses, we uncover that the declined mitochondrial fitness in T cells leads to permanent impairment of proliferative capacity and effector molecule expression and sustained expression of inhibitory receptors. As a result of these actions, T cells accumulating depolarised mitochondria engage senescence/apoptosis and fail to sustain responsiveness to immune checkpoint blockade treatment. Moreover, we conduct an in vivo CRISPR screening to identify metabolic enzymes and kinase that can be targeted for sustaining mitochondrial fitness in CD8 TILs. We are currently in the stage to validate those targets we identify and elucidate how this targeting approach can be exploited in T cell transfer therapy. In the end of this direction, we also finish proteome analysis and are in the process to finish metabolic analysis. We expect the integrated cross-omics analysis will allow us to further explore how mitochondria instruct T cell functionality and differentiation.
In the third direction, as a result of mitochondrial damage, cells will degrade mitochondrial protein to release heme. Intriguingly, heme has been shown to affect B cell differentiation via the regulation of Blimp-1 expression. Given that Blimp-1 is critical transcription factor for orchestrating T cell exhaustion, we aim to explore how heme-mediated program can affect T cell exhaustion in this context. Most importantly, we will develop interventions to abolish this process for ensuring T cell anti-tumor immunity. In the past 18 months, we established assay to measure regulatory heme (freely available in the cytoplasm and nuclei with binding ability to target proteins). Moreover, we confirmed that exhausted T cells do contain more regulatory heme compared to less exhausted T cells and progenitor exhausted T cells in engrafted tumor murine model, inducible melanoma murine model, chronic LCMV infection model and human in vitro T cell exhaustion condition. We further revealed the deregulation of heme can further disrupted circadian clock in T cells, which in turn leads to impaired metabolic adaptation. Morevoer, we are testing how we can improve T cell mediated anti-tumor immunity by targeting heme signaling axis in both T cell transfer and CAR T cell settings.
