Cholesterol-conjugated siRNAs silence gene expression in mucosal dendritic cells in cervicovaginal tissue in mice

RNA interference (RNAi) provides a powerful way to investigate the role of genes in disease pathogenesis and modulate gene expression to treat disease. In 2018, the FDA approved patisiran, the first RNAi-based drug, hence paving the way for a novel class of RNAi therapeutics. Harnessing RNAi to inhibit vaginal HIV transmission requires effective gene silencing in immune cells, which remains difficult. Knockdown in accessible mucosal tissues may be easier than systemic gene silencing. Vaginally applied cholesterol-conjugated small interfering RNAs (chol-siRNAs) blocked herpes simplex virus transmission in mice without tissue damage or immunostimulation.

To investigate using flow cytometry, confocal microscopy, and quantitative imaging if chol-siRNAs silence gene expression in vaginal immune cells in mice.

Although chol-siRNAs and lipoplexed-siRNAs silence gene expression in dendritic cells (DCs) in vitro, most internalized siRNAs concentrate within multivesicular bodies, where they are inaccessible to the cellular RNAi machinery. When applied intravaginally in vivo, chol-siRNAs penetrate the vaginal mucosa, including the lamina propria, and are efficiently internalized by intraepithelial (IE) and lamina propria (LP) DCs, and CD11b⁺ CD45⁺ cells, but not by T cells. Chol-siRNAs induce partial gene silencing in IE and LP DCs throughout the genital mucosa in vivo but are inactive in F4/80⁺ CD11b⁺ macrophages and T cells.

As mucosal DCs play an essential role for mucosal viral entry and dissemination, chol-siRNAs could be harnessed to target various host factors that are critical for viral uptake, DC migration and trans-infection of virions to T cells, hence allowing the development of a preventive vaginal HIV microbicide. Furthermore, chol-siRNAs could help elucidate the pathways of HIV transmission and understand the immunologic function of DCs in the genital tract.