Agonistic nanobodies and antibodies to human VISTA

Broadly Applicable Bispecific Linker Approach to Noncovalently Target Therapeutic Nanoparticles to Tumor Cells Expressing Carcinoembryonic Antigen

Design strategies that lead to a more focused in vivo delivery of functionalized nanoparticles (NPs) and their cargo can potentially maximize their therapeutic efficiency while reducing systemic effects, broadening their clinical applications. Here, we report the development of a noncovalent labeling approach where immunoglobulin G (IgG)-decorated NPs can be directed to a cancer cell using a simple, linear bispecific protein adaptor, termed MFE23-ZZ. MFE23-ZZ was created by fusing a single-chain fragment variable domain, termed MFE23, recognizing carcinoembryonic antigen (CEA) expressed on tumor cells, to a small protein ZZ module, which binds to the Fc fragment of IgG. As a proof of concept, monoclonal antibodies (mAbs) were generated against a NP coat protein, namely, gas vesicle protein A (GvpA) of Halobacterium salinarum gas vesicles (GVs). The surface of each GV was therapeutically derivatized with the photoreactive agent chlorin e6 (Ce6GVs) and anti-GvpA mAbs were subsequently bound to GvpA on the surface of each Ce6GV. The bispecific ligand MFE23-ZZ was then bound to mAb-decorated Ce6GVs via their Fc domain, resulting in a noncovalent tripartite complex, namely, MFE23.ZZ-2B10-Ce6GV. This complex enhanced the intracellular uptake of Ce6GVs into human CEA-expressing murine MC38 colon carcinoma cells (MC38.CEA) relative to the CEA-negative parental cell line MC38 in vitro, making them more sensitive to light-induced cell killing. These results suggest that the surface of NP can be rapidly and noncovalently functionalized to target tumor-associated antigen-expressing tumor cells using simple bispecific linkers and any IgG-labeled cargo. This noncovalent approach is readily applicable to other types of functionalized NPs.

VISTA and its ligands: the next generation of promising therapeutic targets in immunotherapy

V-domain immunoglobulin suppressor of T cell activation (VISTA) is a novel negative checkpoint receptor (NCR) primarily involved in maintaining immune tolerance. It has a role in the pathogenesis of autoimmune disorders and cancer and has shown promising results as a therapeutic target. However, there is still some ambiguity regarding the ligands of VISTA and their interactions with each other. While V-Set and Immunoglobulin domain containing 3 (VSIG-3) and P-selectin glycoprotein ligand-1(PSGL-1) have been extensively studied as ligands for VISTA, the others have received less attention. It seems that investigating VISTA ligands, reviewing their functions and roles, as well as outcomes related to their interactions, may allow an understanding of their full functionality and effects within the cell or the microenvironment. It could also help discover alternative approaches to target the VISTA pathway without causing related side effects. In this regard, we summarize current evidence about VISTA, its related ligands, their interactions and effects, as well as their preclinical and clinical targeting agents.

The IgV domain of the poliovirus receptor alone is immunosuppressive and binds to its receptors with comparable affinity

PVR (poliovirus receptor) functions as a ligand that signals through TIGIT and CD96 to induce suppression of T-cell and NK-cell responses. Alternatively, PVR binds to CD226, resulting in a co-stimulatory signal. To date, TIGIT antibody antagonists have been developed to restore immune functions and allow PVR to signal though CD226 in the context of cancer immunotherapy. Due to PVR receptor heterogeneity, agonizing either of these pathways with a recombinant form of the PVR extracellular domain represents a therapeutic strategy for either immunosuppression or activation. Here, we developed a minimal murine PVR-Fc fusion construct, consisting of only the IgV domain of PVR (vdPVR-Fc), and assessed its ability to dampen inflammatory responses in a murine model of psoriasis. vdPVR-Fc and PVR-Fc containing the full-length extracellular domain bound to TIGIT, CD96 and CD226 with similar low nanomolar affinities as defined by surface plasmon resonance. vdPVR-Fc was also able to suppress the in-vitro proliferation of murine CD4⁺ and CD8⁺ T-cells in mixed splenocyte cultures. Importantly, vdPVR-Fc delayed the onset, and reduced inflammatory responses (scaling and thickness) in a murine model of psoriasis. Collectively, our results suggest that the minimal IgV domain of PVR is sufficient to dampen immune responses in-vitro and attenuate symptoms of psoriasis in-vivo.

Development of Inhibitors Targeting the V-Domain Ig Suppressor of T Cell Activation Signal Pathway

Blockade of cytotoxic T lymphocyte antigen 4 (CTLA-4) and programmed cell death-1/programmed cell death-ligand 1 (PD-1/PD-L1) has produced considerable therapeutic effect, but only in a fraction of patients, so more targets are being investigated. VISTA (V-domain Ig suppressor of T cell activation) is a novel immune checkpoint that is broadly expressed within hematopoietic cells and multiple cancers (low expressing frequency on solid tumors), particularly those with a poor immunotherapy response rate. As a result, VISTA has been identified as an appealing target for immunotherapy, and several VISTA inhibitors are currently in clinical and preclinical trials. In this review, the structural features and binding partners of VISTA are summarized, and we describe the latest developments of monoclonal antibodies and small molecules targeting VISTA as well as possible future directions for development of therapies targeting VISTA.