Uncovering Chitinase-3-like 1 as a Key Regulator of Immune Tolerance and Therapeutic Target in ChordomadissertationsWang, TianyicreatorMartinez-Moreno, MargotAdvisorSullivan, PatriciaReaderLawler, SeanReaderBrown University. Biology and Medicine: Biotechnologysponsor2026, None p.born digitalThesis (Sc. M.)--Brown University, 2026thesesBackground Chordoma is a rare, aggressive cancer with limited treatment options. Chitinase-3-like 1 (CHI3L1), a secreted glycoprotein, is overexpressed in several solid tumors and linked to poor prognosis. In glioma and melanoma, CHI3L1 contributes to an immunosuppressive tumor microenvironment (TME) by modulating immune checkpoint regulators like PD-1/PD-L1. Preliminary data show CHI3L1 is overexpressed in primary chordoma, suggesting a role in its progression. We hypothesized that CHI3L1 promotes immune tolerance by limiting T cell proliferation and upregulating PD-L1 and PD-L2 expression in chordoma. Methods We co-cultured peripheral blood mononuclear cells (PBMCs) and CD8+ T cells from chordoma patients with matched chordoma cells and the JHC-7 cell line. We collected supernatants at set intervals to assess cell viability using CellTiter-Glo and MTT assays. CHI3L1 levels in CD8+ T cell and PBMC supernatants from chordoma, glioblastoma (GBM), and control patients were quantified via ELISA. Expression of checkpoint molecules PD-L1 and PD-L2 upon CHI3L1 introduction was measured using RT-qPCR. Results Exposure to tumor cells or immunogenic signals they secreted was sufficient to stimulate immune cells and increase their viability. Limited T cell proliferation suggested inhibitory T cell targeting mechanisms, supporting the presence of Chi3l1-mediated immune suppression. ELISA confirmed high CHI3L1 in chordoma PBMC monoculture, and co-culturing chordoma PBMCs with JHC-7 induced a synergistic elevation in CHI3L1 secretion. Exposure to recombinant CHI3L1 reduced immune cell viability and induced overexpression of PD-L1 and PD-L2 in JHC-7 cells, confirming the positive correlation between CHI3L1 levels and immune tolerance. Conclusions Findings confirmed active interaction between tumor cells with PBMCs and CD8+ T cells within the chordoma TME in vitro. Differential CHI3L1 secretion in chordoma PBMCs and CD8+ T cells suggests other immune cells, such as CD4+ T cells or macrophages, may contribute to CHI3L1-driven suppression. Exogenous CHI3L1 induced PD-L1 and PD-L2 overexpression, confirming the presence of CHI3L1 mediated immune evasion mechanism. These results position CHI3L1 as a key immunosuppressive factor and potential immunotherapy target in chordoma. Variations in CHI3L1 expression across cancers and immune cells may guide future cell-based cancer therapies.Tumor MicroenvironmentCancer--Immunological aspectsChordomaChitinase-3-like 1immune checkpointEnglishRPB20260516