Effect of siRNA in PEG-coated siRNA-lipoplex on anti-PEG IgM production

Abstract

For efficient delivery of small interfering RNA (siRNA) in vivo, it is important to control the blood circulation of the delivery vehicle. Surface modification of the siRNA/cationic liposome complex (siRNA-lipoplex) with polyethylene glycol (PEG) is expected to enhance circulation time in blood. However, we have recently reported that anti-PEG IgM production after the first injection of PEG-coated liposome is responsible for a reduction in the blood circulation of the second dose of the liposome, which is known as the accelerated blood clearance (ABC) phenomenon. It is unknown whether a PEG-coated siRNA-lipoplex (PSCL) can cause the ABC phenomenon and anti-PEG IgM production. In this study, an anti-PEG IgM response to PSCL was detected and was inversely related to the PSCL dose. Interestingly, the anti-PEG IgM response was significantly lower for PSCL than it was for PEG-coated naked cationic liposomes (PCL). The studies with splenectomized mice and nude mice indicated that anti-PEG IgM production was closely related to an interaction of PSCL and PCL with the spleen, which is associated with a T cell-independent mechanism. In addition, PSCL induced apoptosis on IgM-expressing splenic cells more strongly than PCL did, which suggests that accumulation in the spleen and the apoptotic effect of PEG-coated substances on splenic B cells could affect the potency of anti-PEG IgM production.