Yamashita K(1), Iwatsuki M(1)(2), Yasuda-Yoshihara N(1), Morinaga T(1), Nakao Y(1), Harada K(1)(2), Eto K(1), Kurashige J(1), Hiyoshi Y(1), Ishimoto T(1), Nagai Y(1), Iwagami S(1), Baba Y(1), Miyamoto Y(1), Yoshida N(1), Ajani JA(2), Baba H(3). Author information:
(1)Department of Gastroenterological Surgery, Graduate School of Medical
Sciences, Kumamoto University, Kumamoto, Japan.
(2)Department of Gastrointestinal Medical Oncology, The University of Texas MD
Anderson Cancer Center, Houston, TX, 77030, USA.
(3)Department of Gastroenterological Surgery, Graduate School of Medical
Sciences, Kumamoto University, Kumamoto, Japan. [Email]
BACKGROUND: The predictive significance of programmed death ligand 1 (PD-L1) for programmed death 1 (PD-1) inhibitors remains unclear in gastric cancer (GC) due to the dynamic alteration by treatments. We aimed to elucidate the effects of trastuzumab (Tmab) on PD-L1 expression in GC. METHODS: PD-L1 expression was evaluated by multicolour flow cytometry analysis after co-culturing GG cell lines and immune cells with Tmab. IFN-γ in the co-culture experiments was quantified. Immunohistochemistry (IHC) for PD-L1 expression using clinical samples was also performed to confirm PD-L1 alteration by Tmab. RESULTS: PD-L1 expression was significantly upregulated by Tmab in HER2-amplified GC cell lines co-cultured with peripheral blood mononuclear cells (PBMCs). PD-L1 upregulation by Tmab was also observed in the GC cells co-cultured with NK cells in time-dependent manner, but not with monocytes. IFN-γ concentration in conditioned media from co-cultured PBMCs and NK cells with Tmab was significantly higher and anti-IFN-γ significantly suppress the Tmab-induced PD-L1 upregulation. IHC also suggested PD-L1 upregulation after Tmab treatment. CONCLUSIONS: Tmab can upregulate PD-L1 expression on GC cells through interaction with NK cells. These results suggest clinical implications in the assessment of the predictive significance of PD-L1 expression for PD-1 inhibitors.
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