Ipilimumab differs mechanistically from nivolumab in that it acts predominantly at which stage of the anti-tumor immune response?

• A Effector phase in peripheral tissue, blocking ligand engagement on tumor cells
• B Priming and activation phase in lymph nodes, by blocking CTLA-4 mediated inhibition of T cell costimulation ✓
• C Direct complement-mediated lysis of tumor cells in the bloodstream
• D Antibody-dependent cellular cytotoxicity against regulatory T cells only

Explanation

CTLA-4 competes with CD28 for B7 ligands early in T cell activation within lymph nodes, setting the threshold for priming. Ipilimumab blocks CTLA-4, lowering that threshold and expanding the activated T cell repertoire. PD-1 blockade by nivolumab acts later, at the effector phase in peripheral tissues where PD-L1 on tumor cells dampens engaged T cells. This priming versus effector distinction is the classic contrast asked in exams.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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