Evaluating a Single Domain Antibody Targeting Human PD-L1 as a Nuclear Imaging and Therapeutic Agent.

Broos Broos,Schoonooghe Schoonooghe,Bridoux Bridoux,Lecocq Lecocq,Nguyen Nguyen,Lion Lion,Breckpot Breckpot,Xavier Xavier,Devoogdt Devoogdt,Raes Raes,Corthals Corthals,Keyaerts Keyaerts

doi:10.3390/cancers11060872

Abstract

The PD-1:PD-L1 immune checkpoint axis is central in the escape of cancer cells from anticancer immune responses. Monoclonal antibodies (mAbs) specific for PD-L1 have been approved for treatment of various cancer types. Although PD-L1 blockade has proven its merit, there are still several aspects that require further attention to fully capitalize on its potential. One of these is the development of antigen-binding moieties that enable PD-L1 diagnosis and therapy. We generated human PD-L1 binding single domain antibodies (sdAbs) and selected sdAb K2, a sdAb with a high affinity for PD-L1, as a lead compound. SPECT/CT imaging in mice following intravenous injection of Technetium-99m (99mTc)-labeled sdAb K2 revealed high signal-to-noise ratios, strong ability to specifically detect PD-L1 in melanoma and breast tumors, and relatively low kidney retention, which is a unique property for radiolabeled sdAbs. We further showed using surface plasmon resonance that sdAb K2 binds to the same epitope on PD-L1 as the mAb avelumab, and antagonizes PD-1:PD-L1 interactions. Different human cell-based assays corroborated the PD-1:PD-L1 blocking activity, showing enhanced T-cell receptor signaling and tumor cell killing when PD-1POS T cells interacted with PD-L1POS tumor cells. Taken together, we present sdAb K2, which specifically binds to human PD-L1, as a new diagnostic and therapeutic agent in cancer management.

Highlights

Cancer immunotherapy, which has the purpose to increase the pool of tumor-reactive cytotoxicT lymphocytes (CTLs), has emerged as a promising modality to treat cancer
We previously described the development of single domain antibodies (sdAbs) for nuclear imaging of mouse PD-L1 in syngeneic mouse models [24]
In the current study, we generated a new panel of sdAbs by new alpaca immunizations, biopannings, and screenings on recombinant human PD-L1 protein, and selected among them sdAb K2 as a lead sdAb

Summary

Introduction

Cancer immunotherapy, which has the purpose to increase the pool of tumor-reactive cytotoxicT lymphocytes (CTLs), has emerged as a promising modality to treat cancer. Cancer immunotherapy, which has the purpose to increase the pool of tumor-reactive cytotoxic. Inhibitory immune checkpoint receptors are expressed on CTLs to attenuate their activity. This mechanism avoids overactivation of CTLs, thereby preventing collateral damage and autoimmunity [2]. Cancer cells exploit inhibitory immune checkpoints to dampen antitumor immune responses [3]. Cancer cells of different histology can express programmed death-ligand 1 (PD-L1, CD274, B7-H1), either constitutively or in response to immune-derived signals such as interferon (IFN) [4,5]. The net effect of the interaction between PD-L1 and its receptor, programmed death-1 (PD-1, CD279) on activated CTLs, is that CTLs become paralyzed [8]

Methods

Results

Conclusion