Development of a bispecific antibody targeting PD-L1 and TIGIT with optimal cytotoxicity

Programmed death-ligand 1 (PD-L1) and T cell immunoreceptor with Ig and ITIM domains (TIGIT) are two potential targets for cancer immunotherapy, early clinical studies showed the combination therapy of anti-PD-L1 and anti-TIGIT had synergistic efficacy both in the terms of overall response rate (ORR) and overall survival (OS). It is rational to construct bispecific antibodies targeting PD-L1 and TIGIT, besides retaining the efficacy of the combination therapy, bispecific antibodies (BsAbs) can provide a new mechanism of action, such as bridging between tumor cells and T/NK cells. Here, we developed an IgG1-type bispecific antibody with optimal cytotoxicity. In this study, we thoroughly investigated 16 IgG-VHH formats with variable orientations and linker lengths, the results demonstrated that (G4S)2 linker not only properly separated two binding domains but also had the highest protein yield. Moreover, VHH-HC orientation perfectly maintained the binding and cytotoxicity activity of the variable domain of the heavy chain of heavy-chain-only antibody (VHH) and immunoglobulin G (IgG). Following treatment with BiPT-23, tumor growth was significantly suppressed in vivo, with more cytotoxic T lymphocytes (CTLs) and natural killer (NK) cells infiltration, and selective depletion of Regulatory T cells (Tregs). BiPT-23 represents novel immunotherapy engineered to prevent hyperprogression of cancer with PD-1 blockade, and preferentially killed PD-L1(+) tumor cells, and TIGIT(+) Tregs but maintained CD11b(+)F4/80(+) immune cells within the tumor microenvironment (TME).