Cellular immune correlates conferring protection against respiratory syncytial virus (RSV) but preventing vaccine-enhanced respiratory disease largely remain unclear. We investigated cellular immune correlates that contribute to preventing disease against human respiratory syncytial virus (RSV) by nanoparticle vaccine delivery. Formalin-inactivated RSV (FI-RSV) vaccines and virus-like nanoparticles carrying RSV fusion proteins (F VLP) were investigated in mice. The FI-RSV vaccination caused severe weight loss and histopathology by inducing interleukin (IL)-4+, interferon (IFN)-γ+, IL-4+IFN-γ+ CD4+ T cells, eosinophils, and lung plasmacytoid dendritic cells (DCs), CD103+ DCs, and CD11b+ DCs. In contrast, the F VLP-immune mice induced protection against RSV without disease by inducing natural killer cells, activated IFN-γ+, and IFN-γ+ tumor necrosis factor (TNF)-α+ CD8+ T cells in the lung and bronchiolar airways during RSV infection but not disease-inducing DCs and effector T cells. Clodronate-mediated depletion studies provided evidence that alveolar macrophages that were present at high levels in the F VLP-immune mice play a role in modulating protective cellular immune phenotypes. There was an intrinsic difference between the F VLP and FI-RSV treatments in stimulating proinflammatory cytokines. The F VLP nanoparticle vaccination induced distinct innate and adaptive cellular subsets that potentially prevented lung disease after RSV infection.
Keywords: Alveolar Macrophages; Clodronate Liposome; Formalin-Inactivated RSV; Fusion Protein Nanoparticles; Respiratory Syncytial Virus (RSV).