Increased antitumor activities of glypican-3-specific chimeric antigen receptor-modified T cells by coexpression of a soluble PD1–CH3 fusion protein

Zeyan Pan, Shengmeng Di, Bizhi Shi, Hua Jiang, Zhimin Shi, Ying Liu, Yi Wang, Hong Luo, Min Yu, Xiuqi Wu, Zonghai Li

Our recent clinical study demonstrated that glypican-3 (GPC3)-specific chimeric antigen receptor-modified T (CAR-T) cells are a promising treatment for hepatocellular carcinoma (HCC). However, the interaction of programmed cell death 1 (PD-1) and PD-L1-mediated T-cell inhibition is involved in immune evasion in a wide range of solid tumors, including HCC. To overcome this problem, we introduced a fusion protein composed of a PD-1 extracellular domain and CH3 from IgG4 into GPC3-specific CAR-T cells (GPC3-28Z) to block the PD-1/PD-L1 pathway. GPC3-specific CAR-T cells carrying the PD-1-CH3 fusion protein (sPD1) specifically recognized and lysed GPC3-positive HCC cells. The proliferation capacity of GPC3-28Z-sPD1 T cells after weekly stimulation with target cells was much higher than that of control GPC3-28Z T cells. Additionally, the coexpression of sPD1 could protect CAR-T cells from exhaustion when incubated with target cells, as phosphorylated AKT and Bcl-xL expression levels were higher in GPC3-28Z-sPD1 T cells than in GPC3-28Z cells. Importantly, in two HCC tumor xenograft models, GPC3-28Z-sPD1 T cells displayed a significantly higher tumor suppression capacity than GPC3-28Z T cells. In addition, an increased number of CD3+ T cells in the circulation and tumors and increased granzyme B levels and decreased Ki67 expression levels in the tumors were observed in the mice treated with GPC3-28Z-sPD1 T cells. Together, these data indicated that GPC3-specific CAR-T cells carrying sPD1 show promise as a treatment for patients with HCC.