A versatile platform for the tumor-targeted delivery of immune checkpoint-blocking immunoglobin G

Immunotherapies based on immune checkpoint-blocking antibodies have been considered the most attractive cancer treatments in recent years. However, the systemic administration of immune checkpoint-blocking antibodies is limited by low response rates and high risk of inducing immune-related adverse events (irAEs), which might be overcome by the tumor-targeted delivery of these antibodies. To achieve tumor-targeted delivery, immune checkpoint-blocking antibodies are usually modified with tumor-homing ligands through difficult genetic fusion or chemical conjugation. As most immune checkpoint-blocking antibodies are immunoglobin G (IgG) antibodies, we hypothesize that these IgG antibodies might be noncovalently modified with a tumor-homing ligand fused to an IgG-binding domain (IgBD). To test this hypothesis, the tumor-homing Z_PDGFRβ affibody, which targets platelet-derived growth factor receptor β (PDGFRβ), was fused to the Fab-selective IgBD in a trimeric format. After mixing Z_PDGFRβ fused to the IgBD with immune checkpoint-blocking IgG against programmed death-ligand 1 (αPD-L1), a novel homogenous complex was formed, indicating that αPD-L1 had been successfully modified with Z_PDGFRβ fused to the IgBD. Z_PDGFRβ-modified αPD-L1 bound to both PDGFRβ and PD-L1, thus leading to greater tumor uptake and antitumor effects in mice bearing PDGFRβ⁺PD-L1⁺ tumor grafts. In addition, due to the broad spectrum of IgBD for IgG, immune checkpoint-blocking IgG antibodies against cytotoxic T-lymphocyte-associated protein 4 (αCTLA-4) and signal regulatory protein alpha (αSIRPα) were also modified with Z_PDGFRβ fused to the IgBD. These results demonstrated that a tumor-homing ligand fused to the IgBD might be developed as a versatile platform for the modification of immune checkpoint-blocking IgG antibodies to achieve tumor-targeted delivery.