Delivery with polycations extends the immunostimulant Ribomunyl into a potent antiviral Toll-like receptor 7/8 agonist.

Background: Upper respiratory tract infection is a frequent cause of morbidity worldwide. Although the course of infection is usually mild, it is responsible for enormous social and economic costs. Immunostimulation with bacterial extracts consisting of ribosomal RNA and proteoglycans, such as Ribomunyl, was introduced into the clinic in the 1980s as a new treatment concept, but did not achieve widespread application. Ribomunyl has been proposed to activate innate immunity, but the contribution of its RNA content as well as its antiviral potential has not been studied.

Methods: Peripheral blood mononuclear cells from healthy donors and immune cells from adenoids were incubated with Ribomunyl either by itself or formulated in a complex with cationic polypeptides such as poly-l-arginine or protamine, and induction of cytokines was quantified by ELISA.

Results: Ribomunyl in complex with either poly-l-arginine or protamine, but not on its own, was able to strongly induce interferon-α (P<0.01) and interleukin-12 (P<0.01) in peripheral blood mononuclear cells, whereas induced tumour necrosis factor-α and interleukin-6 levels were independent of the formulation. Comparable results were obtained in immune cells from adenoids, suggesting efficacy also in virus-affected tissue. Cell sorting, RNase digests and selective receptor expression show that the RNA in Ribomunyl acts as an agonist of Toll-like receptor (TLR)7 and TLR8.

Conclusions: Ribomunyl is, in principle, able to potently induce antiviral interferon-α and interleukin-12 via TLR7 and TLR8, respectively, but only when formulated in a complex with cationic polypeptides.