Abstract B005: Molecular, metabolic and functional CD4 T cell paralysis in lymph node impedes tumor control
Authors: Guo Mengdi , Abd-Rabbo Diala , Bertol Bruna , Carew Madeleine , Brooks David G 
Published: December 2023

Abstract
Introduction: CD4 T cells are important in anti-tumor immunity, yet the regulation of CD4 tumor-specific T (TTS) cells during cancer development is still unclear. So far, studies have primarily focused on studying bulk CD4 tumor-infiltrating lymphocytes (TILs) with unknown antigen specificities, or transferring in vitro activated CD4 T cells as adoptive cell therapy (ACT), which fail to directly address how naïve CD4 TTS cells are activated and then differentiate in vivo in response to tumor progression. Therefore, studies addressing these questions will be critical to understand the state of anti-tumor CD4 T cells available for restorative therapies.
Methods: To address these key questions, we developed two murine tumor cell lines, PyMG (an orthotopic breast tumor) and MC38GP (an adenocarcinoma tumor) expressing the LCMV glycoprotein 1-100 sequence (LCMV-GP1-100). The sequence contains an MHCII-epitope GP61-80 and an MHCI-epitope GP33-43, that can be recognized by TCR transgenic CD4 T cells (SMARTAs) and CD8 T cells (P14s), enabling direct in vivo identification of CD4 TTS cells.
Results: We demonstrate that following tumor initiation, CD4 TTS cells are initially primed in the tumor draining lymph node (dLN), but rapidly frozen into a “paralyzed” state. The paralyzed state freezes CD4 TTS cell clonal expansion, impairs differentiation, limits IFNγ production, and redirects metabolic circuits, which together impede tumor control. Transcriptional programming of CD4 TTS cell paralysis is unique to the tumor setting and distinct from well-defined effector and exhaustion programming. In comparison, CD8 TTS cells do not manifest the proliferation defect. Paralysis is actively maintained throughout cancer progression by a functional interplay of regulatory T cells (Tregs) and CTLA4. Depleting Tregs induces robust proliferation of CD4 TTS cells, yet concurrently pushes the proliferated cells to become highly suppressive tumor-specific induced Tregs (iTregs). The differentiation of iTregs is dependent on the CTLA4 expression on CD4 TTS cells. Alleviating suppressive signals from both Tregs and CTLA4 is required to restore CD4 TTS cells proliferation, reduce iTreg differentiation and promote T helper cell differentiation. Overcoming CD4 TTS cell paralysis established long-term tumor control, demonstrating a novel immune evasion mechanism that specifically cripples CD4 TTS cells to favor tumor progression.
Conclusion: Our study demonstrates that during early stages of cancer, the CD4 TTS cell development is quickly paralyzed at multiple levels of functional development. Overcoming their paralysis established long-term tumor control, demonstrating a novel immune evasion mechanism that specifically cripples CD4 TTS cells to favor tumor progression.
Citation Format: Mengdi Guo, Diala Abd-Rabbo, Bruna Bertol, Madeleine Carew, David G Brooks. Molecular, metabolic and functional CD4 T cell paralysis in lymph node impedes tumor control [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Tumor Immunology and Immunotherapy; 2023 Oct 1-4; Toronto, Ontario, Canada. Philadelphia (PA): AACR; Cancer Immunol Res 2023;11(12 Suppl):Abstract nr B005.