EXPRESS: Peripheral ICOS+CD4 T cell frequency: an indicator for short-term progression in resectable advanced gastric cancer following platinum-based chemotherapy.

Background: Peripheral frequency of inducible T cell co-stimulator (ICOS)+CD4 T cells is associated with immunotherapy in gastric cancer (GC); however, limited studies have clarified its association with chemotherapy response.

Methods: This was a prospective, pilot study. A total of 120 participants with newly diagnosed GC and 50 advanced GC patients were recruited; and their prognosis and survival were assessed. The frequency of ICOS+CD4 T cells was examined using flow cytometry.

Results: The frequency of ICOS+CD4 T cells in stage III GC patients was significantly higher than that of other stages patients. In xenograft GC animals, the frequency of ICOS+CD4 in peripheral blood was positively correlated with tumor volume in mice (P=0.0496). High frequency of peripheral ICOS+CD4 was significantly positively correlated with peripheral IFN-γ concentration. Co-culture experiments showed that the presence of GC cells increased the ratio of ICOS+CD4 T cells derived from peripheral blood. The initial peripheral frequency of ICOS+CD4 T cells in the GC progression-group was significantly lower than that in the stable-group after 3 months of platinum-based chemotherapy (P=0.0318).

Conclusion: The frequency of ICOS+CD4 can effectively predicts the short-term progression risk for resectable advanced GC under platinum-based chemotherapy.