Associate Consultant Mayo Clin., Florida, Florida, United States
Disclosure(s):
Imene Hamaidi: No financial relationships to disclose
Introduction/Rationale: Tumor-reactive T cells are characterized by weak T cell receptor (TCR) signaling because of central and peripheral tolerance mechanisms. The suboptimal TCR signaling is further hampered by lack of co-stimulation with concomitant co-inhibitory signaling. The concerted effects of antigen recognition by TCR and co-stimulation/co-inhibition determine the quality of TCR signaling that dictates T cell activation or tolerance. The proximal TCR signaling is precisely tuned to prevent reactivity to self while allowing a protective immune response. Phosphorylation and ubiquitination are the well-known mechanisms controlling TCR signaling.
Methods: We employed flow cytometry and Wb analyses of proximal TCR molecules, calcium flux assay, and RNA-sequencing in Wild-type and Sirt2-deficient T cells. Sirt2 interactome and acetylome were identified via mass spectrometry and immunoprecipitation/Wb analyses. Sirt2 deletion in human tumor-infiltrating lymphocytes (TILs) was achieved by CRISPR/Cas9. The translational potential of Sirt2 blockade was evaluated using Non-Small Cell Lung Cancer (NSCLC) patient-derived xenograft (PDX) mouse models with autologous TILs.
Results: We report that loss of Sirt2, an NAD+-dependent deacetylase, in T cells manifested in amplified calcium mobilization and phosphorylation of key proximal TCR molecules in naïve and anergic T cells. Moreover, Sirt2 deficiency impacted thymic selection and resulted in larger TCR repertoire diversity. Mechanistically, we identified K228 on the linker region of Lck as a specific acetylation target for Sirt2, that is crucial in Lck conformation and activity. Finally, Sirt2 targeting in exhausted murine and human TILs restored their TCR responsiveness and anti-tumor functions.
Conclusion: We reveal protein acetylation modulated by Sirt2 as a previously unrecognized mechanism that modulates the proximal TCR signaling. Thus, Sirt2 targeting may reverse exhausted phenotype of tumor-reactive T cells.
