Inhibition of phagocytic recognition of anti‐D opsonized Rh D+ RBC by polymer‐mediated immunocamouflage

The Rh D antigen posed both a significant clinical risk and inventory supply issue in transfusion medicine. The successful development of the immunocamouflaged RBC has the potential to address both the risk of acute anti‐D transfusion reactions and to improve D− blood inventory in geographic locations where D− blood is rare (e.g., China). The immunocamouflage of RBC was mediated by the covalent grafting of methoxy(polyethylene glycol) to the cell membrane thereby obscuring the D protein from the immune system. To determine the potential efficacy of mPEG‐D+ RBC in D− recipients, anti‐D alloantibodies from previously alloimmunized individuals were utilized. The effects of polymer chain size (2–30 kDa) and grafting concentration (0–4 mM) on antibody binding and erythrophagocytosis were determined using the clinically validated monocyte monolayer assay (MMA) and flow cytometry. The immunocamouflage of D was polymer size and grafting concentration dependent as determined using human anti‐D alloantibodies (both pooled [RhoGAM] and single donors). Importantly, the 20 kDa polymer provided excellent immunocamouflage of D and reached a clinically significant level of protection, as measured by the MMA, at grafting concentrations of ≥1.5 mM. These findings further support the potential use of immunocamouflaged RBC to reduce the risk of acute transfusion reactions following administration of D+ blood to D− recipients in situations where D− units are unavailable or supply is geographically constrained. Am. J. Hematol. 90:1165–1170, 2015. © 2015 Wiley Periodicals, Inc.