Nanobody-based bispecific antibody engagers targeting CTLA-4 or PD-L1 for cancer immunotherapy

As immune checkpoint blockade induces durable responses in only a subset of patients, more effective immunotherapies are needed. Here we present bispecific antibody engagers, fusion proteins composed of a nanobody that recognizes immunoglobulin kappa light chains (VHH_kappa) and a nanobody that recognizes either CTLA-4 or PD-L1. These fusions show strong antitumour activity in mice through recruitment of polyclonal immunoglobulins independently of specificity or isotype. The anti-CTLA-4 VHH-VHH_kappa conjugate demonstrates superior antitumour activity compared with the conventional monoclonal anti-CTLA-4 antibody and reduces the number of intratumoural regulatory T cells in a mouse model of colorectal carcinoma. The anti-PD-L1 VHH-VHH_kappa conjugate is less effective in the colorectal carcinoma model while still outperforming a conventional antibody of similar specificity. The potency of the anti-PD-L1 VHH-VHH_kappa conjugate was enhanced by installation of the cytotoxic drug maytansine or a STING agonist. The ability of such fusions to engage the Fc-mediated functions of all immunoglobulin isotypes is an appealing strategy to further improve on the efficacy of immune checkpoint blockade, commonly delivered as a monoclonal immunoglobulin of a single defined isotype.