16P - Terminally exhausted CD8+ T cells and increased immunosuppressive soluble factors in malignant ascites of patients with gastric cancer with peritoneal metastasis

Background

Peritoneal metastasis is a relatively common manifestation of poor prognosis and resistance to immune checkpoint blockades in patients with gastric cancer (GC). In the present study, we aimed to investigate the exhaustion status of CD8⁺ T cells and immunosuppressive soluble factors in malignant ascites from patients with GC and peritoneal metastasis.

Methods

We obtained pathologically confirmed malignant ascites samples along with peripheral blood from 27 patients with GC peritoneal metastasis and examined the exhaustion status of CD8⁺ T cells using multicolor flow cytometry. A multiplex enzyme-linked immunosorbent assay for immunosuppressive soluble factors, including matrix metalloproteinase-2 (MMP-2), MMP-7, transforming growth factor beta (TGF-β), hepatocyte growth factor (HGF), vascular endothelial growth factor (VEGF), E-cadherin, and angiopoietin-2, was performed on 45 cell-free fluid samples (15 paired malignant ascites and plasma of patients with GC and 15 benign ascites of liver cirrhosis patients).

Results

CD8⁺ T cells in the malignant ascites of GC showed significantly increased expression of PD-1, TIGIT, and TIM-3 compared with peripheral blood CD8⁺ T cells. CD8⁺ T-cells in malignant ascites had more terminally differentiated phenotypes (T-bet^lowEomes^high) and tumor antigen reactivity (CD39⁺ CD103⁺) than peripheral blood CD8⁺ T cells. The expression levels of immunosuppressive soluble factors, including MMP-2, MMP-7, TGF-β, HGF, VEGF, E-cadherin, and angiopoietin-2, were significantly higher in the malignant ascites than in the plasma of patients with GC or in the benign ascites of liver cirrhosis patients.

Conclusions

We found that CD8⁺ T cells in the malignant ascites of GC are terminally exhausted and tumor antigen-reactive T cells. Furthermore, immunosuppressive soluble factors were significantly increased in cell-free fluid of malignant ascites of GC. Thus, the present findings suggest that the co-blockade of immune checkpoints and immunosuppressive soluble factors may be a feasible therapeutic option for patients GC with peritoneal metastasis.

Clinical trial identification

Editorial acknowledgement

Legal entity responsible for the study

The authors.

Funding

Has not received any funding.

Disclosure

All authors have declared no conflicts of interest.