Abstract 5805: Immunomodulatory effects of TG2 in the ovarian cancer tumor microenvironment

Background: Transglutaminase 2 (TG2), an enzyme highly expressed in ovarian cancer (OC) and secreted in malignant ascites, is a key driver of peritoneal metastasis. Previous research has focused on TG2 activity within cancer cells, while the role of TG2 in the tumor microenvironment remained unexplored. Methods: To investigate the impact of host TG2 deficiency on antitumor immunity and tumor progression, we injected ID8 or BPPNM cells intraperitoneally (i.p.) into TG2−/− (TG2KO) and wild-type (WT) (TG2+/+) mice. Synergy with PD-1/PD-L1 immune checkpoint blockade was also investigated. Tumor immune infiltrates within the ascites microenvironment or tumors were determined by high-dimensional spectral flow cytometry (CyTEK) and multiplex IHC (mIHC). To validate the spatially correlated expression of TG2 in tumor and stromal regions with immune cell signaling programs, we conducted spatially indexed transcript profiling (GeoMx digital spatial profiling) of FFPE OC sections. Results: Significantly reduced ascites volume, tumor size, and weight (p<0.05) were observed after ip inoculation of ID8 or BPPNM murine cells in TG2 KO vs. WT mice. Survival of TG2 KO mice bearing BPPNM isografts was longer (p<0.0001) compared to WT mice (64 vs. 46 days). Treatment with anti-PD-L1 antibody inhibited tumor growth in WT and TG2 KO mice, with reduction in ascites and tumor weight in TG2 KO vs control mice (p=0.223 and p=0.053, respectively). There was an overall tendency toward increased CD45+ immune cell density within the TG2-/- ascites microenvironment upon anti-PD-L1 treatment. Frequencies of NK and NKT among CD45+ tumor infiltrates in tumor-bearing TG2-/- mice were increased following anti-PD-L1 compared to the control mice. By contrast, the frequency of immunosuppressive TAMs and PMN-MDSCs was decreased. Although there was no difference in the frequency of B cells, dendritic cells (DC), CD4+ Treg, and CD8+ exhausted-like T cells (TEX) between control and TG2-/- mice, stem-like progenitor exhausted CD8+ T cells were more abundant in TG2-/- mice following anti-PD-L1 treatment. There was a trend to increased density of CD8+ T cells in TG2-/- mice after anti-PD-L1. Tumor-promoting PD-L1+CD11b+ myeloid cells were decreased in tumors from TG2-/- mice following anti-PD-L1 compared with control mice.Co-staining of TG2 and CD8 was used for spatial segmentation analysis in human tumors. TG2 expression in tumor cells and CD8+ T cell infiltration were inversely correlated in stromal areas. An in-depth gene pathway enrichment analysis is underway. Conclusion: The data support the potential of TG2 inhibition to mitigate OC immune evasion and sensitize tumors to immune checkpoint inhibitors. Citation Format: Hao Huang, Ping Xie, Ujin Kim, Longzhen Song, Jianjun Wei, Daniela Matei, Bin Zhang. Immunomodulatory effects of TG2 in the ovarian cancer tumor microenvironment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 5805.