It is assumed that anti-CTLA-4 antibodies cause tumor rejection by blocking negative signaling from B7-CTLA-4 interactions. Surprisingly, at concentrations considerably higher than plasma levels achieved by clinically effective dosing, the anti-CTLA-4 antibody Ipilimumab blocks neither B7 trans-endocytosis by CTLA-4 nor CTLA-4 binding to immobilized or cell-associated B7. Consequently, Ipilimumab does not increase B7 on dendritic cells (DCs) from either CTLA4 gene humanized (Ctla4h/h) or human CD34+ stem cell-reconstituted NSG™ mice. In Ctla4h/m mice expressing both human and mouse CTLA4 genes, anti-CTLA-4 antibodies that bind to human but not mouse CTLA-4 efficiently induce Treg depletion and Fc receptor-dependent tumor rejection. The blocking antibody L3D10 is comparable to the non-blocking Ipilimumab in causing tumor rejection. Remarkably, L3D10 progenies that lose blocking activity during humanization remain fully competent in inducing Treg depletion and tumor rejection. Anti-B7 antibodies that effectively block CD4 T cell activation and de novo CD8 T cell priming in lymphoid organs do not negatively affect the immunotherapeutic effect of Ipilimumab. Thus, clinically effective anti-CTLA-4 mAb causes tumor rejection by mechanisms that are independent of checkpoint blockade but dependent on the host Fc receptor. Our data call for a reappraisal of the CTLA-4 checkpoint blockade hypothesis and provide new insights for the next generation of safe and effective anti-CTLA-4 mAbs.

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The use of antibodies to target immune checkpoints, particularly PD-1/PD-L1, has made a profound impact in the field of cancer immunotherapy. Here, we identified KN035, an anti-PD-L1 nanobody that can strongly induce T-cell responses and inhibit tumor growth. The crystal structures of KN035 complexed with PD-L1 and free PD-L1, solved here at 1.7 and 2.7 Å resolution, respectively, show that KN035 competes with PD-1 (programmed death protein 1) for the same flat surface on PD-L1, mainly through a single surface loop of 21 amino acids. This loop forms two short helices and develops key hydrophobic and ionic interactions with PD-L1 residues, such as Ile54, Tyr56 and Arg113, which are also involved in PD-1 binding. The detailed mutagenesis study identified the hotspot residues of the PD-L1 surface and provides an explanation for the stronger (~1 000-fold) binding of KN035 to PD-L1 than PD-1 and its lack of binding to PD-L2. Overall, this study reveals how a single immunoglobulin-variable scaffold of KN035 or PD-1 can bind to a flat protein surface through either a single surface loop or beta-sheet strands; and provides a basis for designing new immune checkpoint blockers and generating bi-specific antibodies for combination therapy.

Notwithstanding the numerous drugs available for liver cancer, emerging evidence suggests that chemotherapeutic resistance is a significant issue. HGF and its receptor MET play critical roles in liver carcinogenesis and metastasis, mainly dependent on the activity of receptor tyrosine kinase. However, for unknown reasons, all HGF-MET kinase activity-targeted drugs have failed or have been suspended in clinical trials thus far. Macroautophagy/autophagy is a protective 'self-eating' process for resisting metabolic stress by recycling obsolete components, whereas the impact of autophagy-mediated reprogrammed metabolism on therapeutic resistance is largely unclear, especially in liver cancer. In the present study, we first observed that HGF stimulus facilitated the Warburg effect and glutaminolysis to promote biogenesis in multiple liver cancer cells. We then identified the pyruvate dehydrogenase complex (PDHC) and GLS/GLS1 as crucial substrates of HGF-activated MET kinase; MET-mediated phosphorylation inhibits PDHC activity but activates GLS to promote cancer cell metabolism and biogenesis. We further found that the key residues of kinase activity in MET (Y1234/1235) also constitute a conserved LC3-interacting region motif (Y1234-Y1235-x-V1237). Therefore, on inhibiting HGF-mediated MET kinase activation, Y1234/1235-dephosphorylated MET induced autophagy to maintain biogenesis for cancer cell survival. Moreover, we verified that Y1234/1235-dephosphorylated MET correlated with autophagy in clinical liver cancer. Finally, a combination of MET inhibitor and autophagy suppressor significantly improved the therapeutic efficiency of liver cancer in vitro and in mice. Together, our findings reveal an HGF-MET axis-coordinated functional interaction between tyrosine kinase signaling and autophagy, and establish a MET-autophagy double-targeted strategy to overcome chemotherapeutic resistance in liver cancer.

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