Clinical Activity, Toxicity, Biomarkers, and Future Development of CTLA-4 Checkpoint Antagonists

Evidence that the immune system can recognize, and in some cases control or even eliminate tumors, is increasingly clear. Encouraging T-cell activation by blocking regulatory or “checkpoint” molecules is a potent way to amplify anti-tumor immune responses. Successfully exploiting this concept, a new class of anti-cancer therapies, “checkpoint-blocking” antibodies has emerged. The first checkpoint-blocking antibody to enter the clinic was ipilimumab, an antibody that blocks the co-inhibitory receptor cytotoxic T-lymphocyte-associated antigen-4 (CTLA-4). Herein we review the clinical development of CTLA-4 blocking antibodies, including preclinical studies, clinical activity, toxicities, the search for potential biomarkers, and early clinical experience with combinations.