Molecular mechanisms of α4β7 engagement by HIV-1 and implications for vaccine design

HIV-1 transmission is initiated at mucosal surfaces, where the virus engages the gut-homing integrin α4β7 to enhance infectivity and promote early pathogenesis. This review synthesizes molecular, structural, and immunological evidence to describe the context-dependent interaction between the HIV-1 envelope gp120 and α4β7, a receptor expressed on CD4⁺ T cells. The engagement is more than adhesive; it functions as a "molecular handshake" that triggers costimulatory signals, lowers T-cell activation thresholds, promotes virological synapse formation, and drives local differentiation of highly susceptible CCR5⁺ T cells. Virions can also incorporate host α4β7, forming "Trojan horse" particles that home to intestinal tissues. Translational insights highlight the V2 region as a promising vaccine target, with rational immunogen design showing potential to elicit α4β7-blocking antibodies. However, therapeutic α4β7 blockade has yielded mixed results, underscoring the complexity of modulating integrin signaling and the limitations of monotherapy. Moving forward, effective prevention will likely require combination strategies that integrate α4β7-focused immunogens with mucosal immune modulators, guided by physiologically relevant functional assays such as the Mucosal Blocking Score.