Which immunotherapy uses monoclonal antibodies to block PD-1/PD-L1 or CTLA-4 to enhance anti-tumor immunity?

• A. Cytokine therapy with IL-2
• B. Adoptive transfer of NK cells
• C. CAR-T cell therapy
• D. Immune checkpoint inhibitors

Answer: (D)

Immune checkpoint inhibitors use monoclonal antibodies to block inhibitory signals that restrain T cells, boosting anti-tumor immunity. CTLA-4 and PD-1 are brakes on T-cell activation: CTLA-4 competes with CD28 for B7, so blocking CTLA-4 enhances T cell priming and activation; PD-1 on T cells binds PD-L1 in the tumor environment to dampen activity, and blocking PD-1 or PD-L1 reactivates exhausted T cells to attack cancer cells. This mechanism is distinct from cytokine therapy, NK cell transfer, or CAR-T cell therapy, which rely on different approaches rather than blocking these checkpoints with monoclonal antibodies.