Bepirovirsen induces innate immune activation in the liver potentially through TLR8 signaling

Bepirovirsen is an unconjugated antisense oligonucleotide in phase III trials for chronic hepatitis B virus (HBV) infection. Post hoc analyses from a phase IIa study in participants with chronic HBV indicated immediate cytokine production following dosing with bepirovirsen, leading to the hypothesis that bepirovirsen may have innate immune stimulatory activity via pattern recognition receptors (PRRs) in hepatic non-parenchymal cells, alongside its known direct antiviral mechanism in hepatocytes.

Cytokine production was evaluated in phase IIa serum and plasma samples using Myriad RBM, Olink, or MSD panels. Preclinical studies used peripheral blood mononuclear cells (PBMCs) from healthy donors (MSD, flow cytometry) and PRR-overexpressing HEK or THP-1 cells to assess innate immune activation by bepirovirsen. Cytokine protein levels were measured using Luminex or MSD assays in wild-type (WT) and human Toll-like receptor 8 (hTLR8) transgenic mice, while gene expression (reverse-transcription quantitative PCR, RNAscope) was assessed in vivo exclusively in hTLR8 transgenic mice from the Shanghai Model Organisms Center.

Multiple pro-inflammatory cytokines involved in immune cell recruitment and activation were upregulated in bepirovirsen-treated participants. Similar findings were observed preclinically in PBMCs from healthy donors following in vitro exposure to bepirovirsen. Analysis of innate immune activation in PRR-overexpressing cells revealed a weak but statistically significant (p = 0.00085) induction only in the presence of human Toll-like receptor 8 (TLR8). In hTLR8 transgenic mice - but not wild-type mice - bepirovirsen treatment induced pro-inflammatory cytokines, similar to the TLR8 agonist selgantolimod. Kupffer cells and macrophages were identified as the primary responders to bepirovirsen in the livers of hTLR8 mice.

Clinical and preclinical data demonstrate that bepirovirsen elicits an innate immune response, evidenced by induction of inflammatory cytokines. This effect is mediated at least in part by TLR8 activation, complementing its established antiviral mechanism.

The aim of this study was to characterize additional mechanisms of action for bepirovirsen, including immune activation through pattern recognition receptors, based on the hypothesis that bepirovirsen may elicit an innate immune response in addition to its antiviral mechanism. Using phase IIa study samples we show that bepirovirsen induces IFN-γ, TNF, and other cytokines, while in vitro we demonstrate that bepirovirsen harbors innate immune stimulatory activity, potentially through human TLR8. Furthermore, we show that the innate immune activation induced by bepirovirsen is distinct from that of other antisense oligonucleotides. This study demonstrates that bepirovirsen can induce an innate immune response, likely through TLR8 agonism, in addition to its known antiviral mechanism; however, the clinical impact of this immunomodulatory effect remains unclear and requires further investigation.