Human immunodeficiency virus type 1 glycoprotein 120 CD4-induced epitopes (CD4i epitopes)

Human immunodeficiency virus type 1 (HIV-1) glycoprotein 120 (gp120) CD4-induced (CD4i) epitopes are highly conserved regions of the viral envelope protein that become sterically accessible only after the virus binds to the host CD4 receptor (PMID: 12648200). These epitopes, primarily located on the bridging sheet and the base of the V3 loop, constitute the essential binding site for the viral co-receptors CCR5 or CXCR4 (PMID: 9634232). Because they are hidden on the native, unliganded Env trimer, they are often referred to as cryptic epitopes, a feature that allows the virus to evade the host's humoral immune response (PMID: 15105525). In the viral life cycle, these epitopes are critical for the transition from initial receptor attachment to the membrane fusion process. Therapeutic strategies targeting CD4i epitopes include the use of monoclonal antibodies like 17b and 48d, which can neutralize the virus by blocking co-receptor interaction (PMID: 11448988). Additionally, small-molecule CD4 mimetics are being developed to prematurely trigger the exposure of these epitopes, rendering the virus vulnerable to neutralization and antibody-dependent cellular cytotoxicity (ADCC) (PMID: 25505230). Despite their conservation, the therapeutic utility of CD4i antibodies is often limited by their inability to access the epitopes on the pre-fusion, closed conformation of the Env trimer.

Other names

CD4-induced sitesCD4i sitesgp120 bridging sheetCo-receptor binding site epitopesCryptic gp120 epitopes

Neutralization of HIV-1 by blocking the interaction between the gp120 bridging sheet and host co-receptors (CCR5 or CXCR4), and sensitization of infected cells to antibody-dependent cellular cytotoxicity (ADCC) through the exposure of cryptic epitopes.