Immunotherapy targeting immune checkpoints (ICPs), such as programmed death‐ligand‐1 (PD‐L1), is used as a treatment option for advanced or metastatic non‐small cell lung cancer (NSCLC). However, overall response rate to anti‐PD‐L1 treatment is limited due to antigen heterogeneity and the immune‐suppressive tumor microenvironment. Human leukocyte antigen‐G (HLA‐G), an ICP as well as a neoexpressed tumor‐associated antigen, is previously demonstrated to be a beneficial target in combination with anti‐PD‐L1. In this study, a nanobody‐based trispecific T cell engager (Nb‐TriTE) is developed, capable of simultaneously binding to T cells, macrophages, and cancer cells while redirecting T cells toward tumor cells expressing PD‐L1‐ and/or HLA‐G. Nb‐TriTE shows broad spectrum anti‐tumor effects in vitro by augmenting cytotoxicity mediated by human peripheral blood mononuclear cells (PBMCs). In a humanized immunodeficient murine NSCLC model, Nb‐TriTE exhibits superior anti‐cancer potency compared to monoclonal antibodies and bispecific T cell engagers. Nb‐TriTE, at the dose with pharmacoactivity, does not induce additional enhancement of circulating cytokines secretion from PMBCs. Nb‐TriTE effectively prolongs the survival of mice without obvious adverse events. In conclusion, this study introduces an innovative therapeutic approach to address the challenges of immunotherapy and the tumor microenvironment in NSCLC through utilizing the dual ICP‐targeting Nb‐TriTE.

Animal coronaviruses (CoVs) have been identified to be the origin of Severe Acute Respiratory Syndrome (SARS)-CoV, Middle East respiratory syndrome (MERS)-CoV, and probably SARS-CoV-2 that cause severe to fatal diseases in humans. Variations of zoonotic coronaviruses pose potential threats to global human beings. To overcome this problem, we focused on the main protease (M^pro), which is an evolutionary conserved viral protein among different coronaviruses. The broad-spectrum anti-coronaviral drug, GC376, was repurposed to target canine coronavirus (CCoV), which causes gastrointestinal infections in dogs. We found that GC376 can efficiently block the protease activity of CCoV M^pro and can thermodynamically stabilize its folding. The structure of CCoV M^pro in complex with GC376 was subsequently determined at 2.75 Å. GC376 reacts with the catalytic residue C144 of CCoV M^pro and forms an (R)- or (S)-configuration of hemithioacetal. A structural comparison of CCoV M^pro and other animal CoV M^pros with SARS-CoV-2 M^pro revealed three important structural determinants in a substrate-binding pocket that dictate entry and release of substrates. As compared with the conserved A141 of the S1 site and P188 of the S4 site in animal coronaviral M^pros, SARS-CoV-2 M^pro contains N142 and Q189 at equivalent positions which are considered to be more catalytically compatible. Furthermore, the conserved loop with residues 46–49 in animal coronaviral M^pros has been replaced by a stable α-helix in SARS-CoV-2 M^pro. In addition, the species-specific dimerization interface also influences the catalytic efficiency of CoV M^pros. Conclusively, the structural information of this study provides mechanistic insights into the ligand binding and dimerization of CoV M^pros among different species.