α4 integrin blockade impairs CD8 T cell neuroimmune surveillance following SIV infection

Integrin-targeted therapies are under investigation for HIV associated neuroinflammation, yet their impact on CNS anti-viral 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.