A Novel Regulator of Antitumor Immunity and Immunotherapy

ABSTRACT Tumor antigen-triggered T cell receptor (TCR) signaling in the cytoplasm and transcriptional/epigenetic control in the nucleus are central to CD8+ T cell-dependent antitumor immunity. However, strong and persistent antigen stimulation leads to immune exhaustion. Compared to tumor drainage lymph nodes, the tumor

microenvironment (TME) contains higher amounts of tumor antigens and their prolonged presentation to tumor- infiltrating CD8+ T cells can exacerbate T cell exhaustion and immune evasion. Except for co-inhibitory receptors, it is largely unknown how T cells adapt to the antigen-rich milieu of TME. Better understanding of the mechanisms

underlying TME-unique regulation of T cell functions could inform novel therapies aimed at reinvigorating the antitumor potential of exhausted CD8+ T cells. The overarching scientific objective of our proposed work is to determine how negative elongation factor (NELF), known for its function in RNA polymerase II (Pol II) pausing, regulates CD8+ T cell activities in a TME-

unique manner. Our preliminary work suggests that NELF is both necessary and rate-limiting in promoting the antitumor activity of CD8+ T cells. Of note, this NELF function is unique to CD8+ T cells within the TME, but not in tumor drainage lymph nodes. Furthermore, our published and unpublished data point to potential dual actions

of distinct subcellular pools of NELF: while nuclear NELF participates in transcriptional and epigenetic programs, cytoplasmic NELF attenuates TCR signaling. We hypothesize that the combined actions of NELF likely contribute to stronger T cell memory and less T cell exhaustion. Built upon rigorous scientific premises and

multidisciplinary expertise, we will validate this novel hypothesis by deciphering the TME-unique function of NELF (Aim 1), interrogating its dual molecular actions in the nucleus and cytoplasm (Aim 2), and exploring the utility of NELF overexpression in boosting efficacy of anticancer immunotherapies (Aim 3).

The concept that NELF has a TME-unique function in antitumor immunity is novel. Furthermore, the proposed dual actions of NELF clearly deviate from the Pol II pausing-exclusive paradigm of NELF biology. The proposed work in this multi-PI R01 proposal promises to shed light on a previously unappreciated regulator of TME-unique

functions of tumor-infiltrating T cells, with potential for a sustained impact on the understanding of antitumor immunity. From a translational perspective, discoveries from this project could inform more effective approaches to boost T cell memory and overcome T cell exhaustion, thus helping address a significant barrier and unmet

clinical need in anticancer immunotherapies.