Which antiretroviral class blocks viral entry by targeting the CCR5 receptor?

• A. Reverse transcriptase inhibitors
• B. CCR5 receptor antagonists (entry inhibitors)
• C. Protease inhibitors
• D. Integrase inhibitors

Answer: (B)

Blocking viral entry by targeting the CCR5 receptor relies on HIV’s use of CCR5 as a co-receptor to get into CD4+ T cells. The drug binds to CCR5 on the cell surface, preventing HIV gp120 from engaging this co-receptor. Without this interaction, the fusion process can’t complete, so the virus cannot enter the cell. This approach specifically blocks viruses that use CCR5 (R5-tropic); strains that use CXCR4 (X4-tropic) or can use both are not inhibited by CCR5 antagonists. A common example is maraviroc.

This mechanism is distinct from other antiretroviral classes that act after entry: reverse transcriptase inhibitors stop the viral RNA from being reverse-transcribed into DNA; protease inhibitors prevent maturation of viral proteins; integrase inhibitors block the integration of viral DNA into the host genome. Because only certain viral strains rely on CCR5, tropism testing is usually performed before using this drug, and there can be a shift to CXCR4 use that reduces effectiveness.