High-affinity human PD-L1 variants attenuate the suppression of T cell activation.

The activated T cells can be suppressed by programed death-1 (PD-1) axis through low affinity interaction between PD-1 and PD-ligand 1 (PD-L1) in solution or on antigen presenting cells. In clinic, the concentration of soluble PD-L1 in peripheral blood negatively correlates with cancer prognosis. However, there is little information about the relation between the affinity of PD-1/PD-L1 interaction and the suppressive capacity of PD-1 axis. In this study, we analyzed inhibitory roles of high affinity soluble human PD-L1 (hPD-L1) variants, which were generated with directed molecular evolution. Resultant two clones L3C7-hPD-L1 and L3B3-hPD-L1 showed over 20 folds greater affinity than that of native hPD-L1. We found that L3B3-hPD-L1 and L3C7-hPD-L1 could compete with an anti-PD-1 antibody (EH12.1) for binding to hPD-1. More importantly, although native soluble hPD-L1 can induce suppressive effects on activated T cells, we found L3B3-hPD-L1 and L3C7-hPD-L1 attenuated the strength of PD-1 axis for suppressing the proliferation and interferon γ (IFN-γ) secretion of PBMC. In conclusion, our data provide direct evidence in which immune checkpoint receptor-ligand interactive strength can alter the the suppressive function, in particular, the suppressive capacity of PD-1 axis could be decreased with enhanced affinity of soluble PD-L1 and PD-1 interaction. Our study might provide a new direction for manipulating immune checkpoints.

Systemic therapy for esophagogastric cancer: immune checkpoint inhibition.

The poor prognosis for patients with esophagogastric cancers (EGC) requires the development of newer more effective therapies to further improve the treatment outcomes for this disease. Immunotherapy is a novel treatment strategy that is dramatically changing the treatment landscape for several types of cancers. Cytotoxic T lymphocyte antigen-4 (CTLA-4) and programmed death the programmed death (PD)-1/PD-ligand are essential immune checkpoint inhibitors that suppress T cell activation. Targeting of these immune checkpoints with monoclonal antibodies has shown clinical efficacy in several solid tumors which has led to their approval and use in routine clinical practice. In EGC early phase evaluation of immune checkpoint inhibitors has yielded encouraging results with multiple phase 3 studies currently ongoing. In this review, the biological rationale for the use of immune checkpoint inhibitors in cancer will briefly be described and the accumulating data concerning their use in EGC will be presented.