The results of the RV144 trial demonstrated that vaccination could prevent HIV transmission in humans and that longevity of anti-Env antibodies may be key to this protection. Efforts to improve upon the prime-boost vaccine regimen used in RV144 have indicated that booster immunizations can increase serum anti-Env antibody titers but only transiently. Poor antibody durability hampers efforts to develop an effective HIV-1 vaccine. This study was designed to identify the specific elements involved in the immunological mechanism necessary to produce robust HIV-1-specific antibodies in rhesus macaques. By clearly defining immune-mediated pathways that improve the magnitude and functionality of the anti-HIV-1 antibody response, we will have the foundation necessary for the rational development of an HIV-1 vaccine.

Integrin-targeted therapies are under investigation for HIV-associated neuroinflammation, yet their effect on CNS antiviral immunity remains undefined. We examined the role of α4 integrin in T cell–mediated neuroimmune surveillance using SIV-infected macaques with α4 blockade and T cell–specific α4-deficient mice. In macaques, α4 blockade preserved CD4 ⁺ Th1 cell access to the brain parenchyma but impaired CD8 effector recruitment, disrupting antiviral control. Despite stable cerebrospinal fluid viral loads, hippocampal SIV RNA increased under blockade. Single-cell analyses revealed α4 enrichment in CD8 effector memory (Tem) cells; blockade reduced inferred CD8 ⁺ Tem-monocyte interactions and heightened innate immune activation in the hippocampus. Microscopy demonstrated persistent SIV-induced microglial simplification despite treatment. Th1 CD4 effectors correlated positively with gray matter viral RNA, whereas α4β7 ⁺ CD8 ⁺ T cells correlated inversely, implicating impaired CD8 ⁺ Tem recruitment in elevated parenchymal viral burden. In mice, α4 proved dispensable for CD4 trafficking to inflamed brain but essential for CD8 effector access across CNS compartments and for both subsets to reach skull marrow. These findings establish that α4 integrin governs CD8-mediated neuroimmune surveillance through coordinated cellular positioning, with blockade enabling viral seeding while disrupting spatially organized antiviral defense.