Neutrophils-mediated accelerated blood clearance phenomenon in beagles and rats based on the cross-injection of non-PEGylated and PEGylated nanoemulsions.

The initial injection of PEGylated nanoparticles can activate antibodies and the complement system, leading to the accelerated blood clearance (ABC) phenomenon, characterized by reduced circulation time and abnormal liver and spleen accumulation upon re-exposure. However, PEGylation is not essential for ABC induction, as non-PEGylated nanoparticles can also trigger the similar ABC phenomenon. In this study, we found non-PEGylated nanoemulsions (CE) could accelerate the blood clearance of subsequent injection of PEGylated nanoemulsions (PE) in beagles and rats, which was independent of antibodies and the complement system, but was associated with an increase in neutrophil numbers and phagocytic activity. We propose classifying this as a "general ABC phenomenon," broadening clinical relevance and highlighting potential immune risks of ABC phenomenon. The intensity of the ABC phenomenon correlated with the initial CE phospholipid dose in both species. Notably, larger CE particles (∼ 300 nm) induced the ABC phenomenon in beagles, while smaller particles (∼ 80 nm) with higher immunogenicity were required in rats. This suggested that beagles are more susceptible to CE-induced ABC phenomenon. The higher neutrophil proportion in beagles likely contributed to species differences in ABC phenomenon. This is the first study to report neutrophil involvement in ABC induction by non-PEGylated nanoparticles, more importantly, underscoring potential immune risks in the cross-injection of non-PEGylated and PEGylated nanoparticles during the developments and clinical applications of nano-drug delivery systems.