Development of recombinant antibodies targeting T cell co-inhibitory molecule VISTA (V-domain Ig Suppressor of T Cell Activation)

Abstract

For T-cell activation to occur two signals are required, the first signal consists of the T cell receptor (TCR) interacting with the peptide complexed with the major histocompatibility complex (pMHC) and the second signal consists of the interaction between co-stimulatory molecules. One mechanism by which tumour microenvironment (TME) can inhibit T-cell activation is by inhibiting the expression of co stimulatory molecules or increasing the expression of co-inhibitory molecules. In immunotherapy, these co-inhibitory molecules are being targeted by monoclonal antibodies (mAbs) known as immune checkpoint inhibitors (ICIs) to inhibit their effect which in turn can stimulate the anti-tumour immune response. Currently, there are two Food and Drug Administration (FDA) approved ICIs that target the Cytotoxic T-lymphocyte-associated Antigen-4 (CTLA-4) and Programmed Death-1 (PD-1) which are effective in controlling tumour progression and increasing the survival rate. However, due to extrinsic and intrinsic mechanisms that are constantly evolving in the TME, these ICIs have a high rate of acquired resistance. For this reason, other co-inhibitory molecules are being investigated to be used alone or in combination with other treatments to increase the effectivity and reduce the rate of acquired resistance. The V-domain immunoglobulin suppressor of T cell activation (VISTA) is one of these molecules that is being currently studied and will be the main focus of this study. In this study, an in vitro Single chain variable fragments (ScFV) phage display library which has been biopanned for 4 rounds and immobilized using magnetic beads and the plate technique was used. After 4 rounds of biopanning Abs were successfully generated to bind specifically with VISTA than with the IgG and TIM-3 negative controls. During biopanning immobilization by magnetic beads was found to be more effective to produce higher affinity antibodies than immobilization with the plate technique.