Ipilimumab differs from nivolumab and pembrolizumab in its checkpoint target. The immune-inhibitory receptor blocked by ipilimumab, and the predominant site of its expression, are:
- A CTLA-4 on activated T lymphocytes ✓
- B PD-L1 on tumour cells
- C LAG-3 on regulatory T cells
- D TIM-3 on dendritic cells
Correct answer: A. CTLA-4 on activated T lymphocytes
Explanation
Ipilimumab is a fully human IgG1 antibody against CTLA-4 (CD152), expressed on activated T cells and regulatory T cells. CTLA-4 competes with CD28 for A7 ligands (CD80/CD86) on antigen-presenting cells during priming in lymph nodes, so blockade enhances T-cell activation at the priming phase. PD-1/PD-L1 agents act later, at the effector phase in peripheral tissues. LAG-3 and TIM-3 are targets of investigational or newer agents, not ipilimumab.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
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