High-affinity human programmed death-1 ligand-1 variant promotes redirected T cells to kill tumor cells

Tumor cells can escape immune surveillance through the programmed cell death protein 1 (PD-1) axis suppressing T cells. However, we recently demonstrated that high-affinity variants of soluble human programmed death-ligand 1 (shPD-L1) could diminish the suppression. We propose that in comparison to the wild-type shPD-L1, the further affinity enhancement will confer the molecule with opposite characteristics that augment T-cell activation and immunotherapeutic drug potential. In this study, a new shPD-L1 variant, L3C7c, has been generated to demonstrate ∼167 fold greater affinity than wild-type hPD-L1. The L3C7c-Fc fusion protein demonstrated completely opposite effects of conventional PD-1 axis by promoting redirected T-cell proliferation, activation and cytotoxicity in vitro, as being slightly better than that of anti-PD1-Ab (Pembrolizumab). Moreover, L3C7c-Fc was more effective than Pembrolizumab in enhancing redirected T cells' ability to suppress Mel624 melanoma growth in vivo. As a downsized L3C7c-Fc variant, L3C7v-Fc improved the anti-tumor efficacy in vivo when combined with dendritic cell vaccines. In conclusion, our studies demonstrate that high-affinity hPD-L1 variants could be developed as the next generation reagents for tumor immunotherapy based on the blockade of the PD-1 axis.