53L10 T-cell engager tribody for immunotherapy of multiple solid tumors.

Cancer immunotherapy with immune checkpoint inhibitors (ICIs), i.e., antibodies targeting inhibitory ICs, such as PD-1, PD-L1, and CTLA-4, have successfully revolutionized cancer treatment. One of the most promising cancer immunotherapies is based on bi-specific T-cell engagers that simultaneously bind with one arm to a tumor-associated antigen on tumor cells and with the other one to the CD3 complex on T cells to form a TCR-MHC-independent immune synapse. We previously generated four novel tribodies, tri-specific antibody derivative constructs, made up of a Fab targeting 5T4, an oncofetal tumor antigen expressed on several types of tumors, an scFv targeting CD3 on T cells, and an additional scFv specific for an immune checkpoint. In particular, the 53L10 tribody, targeting PD-L1, displayed the best binding properties and stronger anti-tumor activity in vitro and in vivo in mouse models. Here, we further investigated the anti-tumor potential of 53L10 by testing its effects on a panel of tumor cell types with a more aggressive profile, including gastric, pancreatic, prostate, ovarian, and epidermoid tumor cells. We found that 53L10 was very effective on these cells by inducing stronger T-cell activation and tumor cell lysis than the parental bi-specific 53P lacking an ICI. To further test its therapeutic potential, we also analyzed its stability and the effects on tumor T-cell infiltration in vivo on a mouse model. 53L10 was found to be stable after incubation in serum at 37 °C for 3 days and induced a more efficient and earlier increase in tumor tissues of both CD4 and CD8 T cells than the parental bi-specific 53P. These findings support further preclinical evaluation of 53L10 as a new tool for multiple solid tumor-targeted therapeutic approaches.