Investigating the redox-sensitive E3 ubiquitin ligase Pellino-1 as a driver of T-cell dysfunction during severe lung infection

PROJECT SUMMARY Patients with hematologic cancer are at increased risk of morbidity and mortality from severe lung infections due to both disease and treatment-associated defects in cell-mediated and humoral immunity. CD8 T cell immunity is critical for survival from these infections, as evidenced by our laboratory’s findings in patients with hematologic cancer and severe COVID-19 infection. However, persistent antigen exposure during severe infections leads to loss of T-cell cytotoxic effector function and proliferative capacity, leading to inefficient pathogen clearance. Therefore, strategies to reverse CD8 T cell dysfunction represent a critical unmet need in patients with hematologic cancer and severe lung infections. Our laboratory previously demonstrated that mitochondrial redox stress drives CD8+ T-cell dysfunction during persistent antigen exposure in a manner that can be reversed by the antioxidant N-acetylcysteine (N-Ac) and recently completed a clinical trial of N-Ac in cancer patients with severe COVID-19 infection. In my preliminary studies, I found that circulating CD8 T cells from patients with cancer and severe COVID-19 had significantly reduced expression of Pellino-1 (PELI1) following N-Ac treatment. PELI1 is an E3 ubiquitin ligase known to negatively regulate CD8 T-cell activation. However, its role in limiting CD8 T-cell function during severe infections remains unknown. Therefore, my hypothesis is PELI1 is a redox-sensitive E3 ligase that limits CD8 T cell immunity during severe respiratory infections by selectively degrading substrates essential for self-renewal and cytotoxicity. We will address this hypothesis through the following Specific Aims. In Aim 1, I will test the hypothesis that PELI1 limits CD8+ T cell immunity during severe respiratory infections in vivo, by analyzing primary samples from hematologic cancer patients with a variety of respiratory infections as well as by determining the impact of PELI1 knockout on T-cell mediated pathogen clearance in mouse models of severe pneumonia. In Aim 2, I will determine the mechanism by which PELI-1 restricts CD8+ T-cell function during persistent antigen exposure. By performing biochemical and proteomic analyses to identify both PELI1 substrates and redox-dependent post- translational modifications in PELI-1 to gain insight into mechanisms of PELI1 function and regulation. The information obtained from this project will lay the groundwork for understanding of how redox regulation impacts T-cell dysfunction, thereby paving the way for innovative therapeutic strategies for patients with severe respiratory infections, including those with concurrent hematologic cancers.