Immunological impact of ramucirumab on tumor microenvironment in advanced gastric cancer.

Abstract

98 Background: Ramucirumab (RAM), a monoclonal antibody against VEGFR2, was recently approved for the treatment of advanced gastric cancer (GC). However, little is known about the immunological effects in advanced GC patients. Methods: Patients with advanced GC who had been planned to receive chemotherapy containing RAM were prospectively enrolled for this study from January 2016 to September 2016. Paired samples were obtained from peripheral blood mononuclear cells (PBMCs) and tumor infiltrating lymphocytes (TILs) in primary tumors pre- and post-RAM therapy to investigate immune profiles. Results: A total of 59 PBMCs and TILs from 18 patients were collected. Higher frequencies of FOXP3highCD45RA-CD4+ T cells (effector regulatory T cells: eTregs) were detected in TILs compared with PBMCs (19.05±10.48% vs 1.89±1.0%, P < 0.0001), and the presence of high eTreg in TILs was not reflected in PBMCs. eTregs of TILs, but not of PBMC were significantly decreased after RAM-containing therapies (22.67±11.19% vs. 16.33±8.44%, P = 0.034). Expressions of immune checkpoint (IC) molecules (PD-1, CTLA-4, LAG-3, and ICOS) were much higher in TILs than those in PBMCs, and all these molecules exhibited higher expressions on eTregs than on CD8+ T cells. Among them, ICOS was specifically expressed by eTregs in TILs. PD-1+CD8+ T cells in TILs were significantly decreased after RAM-containing therapies (54.99±19.06% vs. 39.23±17.15%, P = 0.0005), but not in PBMC. Patients with partial responses had significantly higher frequency of eTreg in pre-treatment TIL than those with progression disease (32.56±12.11% vs. 14.83±3.18%, P = 0.036). Furthermore, patients with high eTreg frequency had significantly longer progression-free survival than those with low frequency (161 days vs. 76 days, P = 0.024). Conclusions: There was significant difference in immune profile between PBMC and TIL in GC patients. eTregs and PD-1 expression on CD8+T cells in TILs, not in PBMCs were decreased after RAM-containing therapies. This observation suggests the importance of TIL analyses and might be a rationale to use RAM as an immunomodulator in combination with IC inhibitors.