Exogenous CD55 Expression on Membrane-Wrapped Nanoparticles Unexpectedly Increases Spleen Tropism and Immune Cell Uptake <i>In Vivo</i>

Intravenously delivered nanoparticle (NP) therapies have the potential to cure a variety of diseases; however, their clinical use has been stunted by undesirable levels of immune cell clearance. This clearance is attributed to protein adsorption onto the outside of the NPs, leading to recognition by immune cells and subsequent accumulation in the liver and spleen. Membrane-wrapped nanoparticles (MWNPs) offer a potential solution to reducing immune clearance by incorporating immune evasion/marker-of-self-proteins, although they too exhibit protein corona-mediated clearance. While various opsonin proteins can bind to MWNPs, complement proteins are particularly problematic as they play a crucial role in innate immunity, triggering immune cell recognition and clearance and causing inflammation. We hypothesized that introducing a complement regulatory protein into the membranes of MWNPs could minimize complement-mediated clearance, but the opposite effect was observed experimentally. In this study, before membrane collection, source cells were genetically modified to express the complement regulatory protein, CD55, which inhibits C3 convertases, key enzymes in the complement cascade. We confirmed that the active protein was transferred onto MWNPs and determined that CD55-modified MWNPs incubated in mouse serum significantly reduced C3 convertase concentration by 33% compared to unmodified MWNPs. Unexpectedly, <i>in vivo</i> analysis of biodistribution and immune cell uptake showed that CD55-modified MWNPs exhibited 2.1× higher spleen accumulation and elevated immune cell uptake in blood and spleen, specifically in monocyte/macrophage populations, as compared to unmodified MWNPs. This may be due to nonprotein corona-mediated mechanisms, such as the secondary role of CD55 as a ligand for CD97 (expressed in monocytes, macrophages, and other immune cells). Supporting this theory, studies examining <i>ex vivo</i> MWNP binding to spleen cells pretreated with IgG or CD97 antibodies showed that CD55-modified MWNPs had 18% lower binding after CD97 blockade, whereas unmodified MWNP binding was not reduced by CD97 blockade. These findings highlight the importance of considering both serum protein interactions and ligand/receptor interactions when designing genetically engineered MWNPs that overexpress a protein of interest, as well as the importance of testing modified MWNPs in both <i>ex vivo</i> and <i>in vivo</i> settings. In the future, the CD55 modification described here could be utilized to promote spleen tropism of MWNPs when desired. More broadly, this work demonstrates the ability to tune MWNP cellular interactions and biodistribution through genetic engineering of source cellsa technique that can be adapted for a plethora of uses in precision medicine.