Immune checkpoints are essential for preventing immunopathology but can also obstruct anti-tumor immune responses. Recent medical advances in blocking these mechanisms have therefore opened promising avenues in the treatment of cancer. Various blocking antibodies targeting the immune checkpoints programmed cell death 1 (PD-1) and cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) are now approved for human use. This review summarizes the properties of PD-1 and CTLA-4 in physiological and tumor settings, and examines the treatment efficacy, side effects and biomarkers of their inhibitors. Future avenues in the application and development of immune checkpoint inhibitors for the treatment of cancer are also explored.

CTLA-4; PD-1; cancer; immunotherapy; side effects; biomarkers

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