Improving anti–CTLA-4 therapies through peptide masking and fragment crystallizable non‑fucosylation: preclinical characterization of three novel antibodies

Abstract Background: The anti-cytotoxic T-lymphocyte antigen 4 (CTLA-4) monoclonal antibody, ipilimumab, has shown clinical benefit across multiple tumor types, both as monotherapy and in combination with nivolumab or chemotherapy. However, not all tumors respond, and peripheral effects can lead to immune-related adverse events. We characterized three novel anti–CTLA-4 antibodies: peptide-masked (PROBODY® conditionally activatable therapeutic PB), nonfucosylated (NF), and combined NF-PB (BMS-986288). Methods: We evaluated the preclinical characteristics, including the pharmacodynamics, tolerability, antitumor activity and efficacy, and peripheral immune responses, of these novel anti–CTLA-4 antibodies using in vitro systems, animal models, and human data. This includes data in preclinical mouse models of colorectal cancer as well as non-small cell lung cancer. Results: NF demonstrated greater T-cell priming and antitumor activity than both ipilimumab and the unmasked PB antibody in cell-based assays and mouse models. Whereas the intact PB antibody showed minimal CTLA-4 binding and peripheral immune activation, unmasking restored its functional activity to levels comparable with those of ipilimumab. Unmasked anti–CTLA-4 NF-PB retained the effectiveness of anti–CTLA-4 NF, and both molecules demonstrated more profound antitumor activity, increased effector memory T-cell response, and prolonged survival in mouse models compared with ipilimumab. Anti–CTLA-4 NF-PB demonstrated reduced peripheral immune responses than anti–CTLA-4 NF or ipilimumab in non-human primates and patients with solid tumors. Conclusion: Anti–CTLA-4 NF-PB has enhanced antitumor activity, efficacy, and reduced peripheral activity in preclinical models, and has the potential to provide therapeutic benefit in solid tumors.