1228 Comprehensive T-cell Profiling in Chordomas: Single-cell RNA-Seq and TCR Profiling Analysis Uncover Antitumor and Exhaustion Phenotypes for Targeted Immunotherapies

INTRODUCTION: Chordomas, a rare type of tumor, originate from residual notochord tissue. These tumors present important challenges due to the limited treatment options. Investigating the intricacies of T-cell composition and function in chordoma immunity holds the potential to advance immunotherapy strategies for these patients. METHODS: We generated a comprehensive single-cell atlas of T cells of chordomas, incorporating paired single-cell transcriptomic samples from the tumor and blood of five patients and single-cell TCR sequencing data to assess T-cell clonality. Additionally, we analyzed T cells in 33 chordomas (22 newly diagnosed and 11 recurrent tumors) using multiplex immunofluorescence. RESULTS: Our results demonstrate that CD8+ T-cell antitumoral immunity originates in the periphery, marked by clonal expansion of cytotoxic and memory T cells in the blood. However, this immunity experiences progressive exhaustion upon tumor infiltration. Notably, a large percentage of CD8+ T-cells from the tumors and blood shared their TCRs with exhausted CD8+ T-cells known for tumor specificity, confirming the origin of a peripheral antitumor response. We identified specific antigen peptide sequences through TCR analysis that were enriched in exhausted T cell receptors' binding sites that uncovered shared motifs within the reactive tumor-infiltrating compartment. Moreover, we observed that CTLA-expressing central memory and Tregs made up most of the CD4 T-cell tumoral landscape. Interestingly, multiplex immunofluorescence showed a higher abundance of CD3+ T cells in newly diagnosed chordomas compared to recurrent cases. CONCLUSIONS: This study sheds light on the composition and function of T cells in chordomas, revealing the origin and exhaustion of CD8+ T-cell antitumor immunity. These findings contribute to our understanding of chordoma immunity to guide the development of targeted immunotherapies for both newly diagnosed and recurrent cases.