Harnessing bispecific antibodies to target immunologically stealth particles

Although essential for human health, the innate immune system represents a major biological barrier to the medical applications of nano-engineered particles. Opsonisation and phagocytosis sequester particles from the... [ view full abstract ]

Although essential for human health, the innate immune system represents a major biological barrier to the medical applications of nano-engineered particles. Opsonisation and phagocytosis sequester particles from the circulation to the detriment of therapeutic delivery. We have previously developed long-circulating polyethylene glycol (PEG) particles with a unique ability to evade phagocytic cell uptake. However, these ‘stealth’ particles lack cell targeting abilities. Now, in an effort to engineer cell targeting into stealth materials, we developed bispecific antibodies (BsAb) that display dual specificity; one arm binds PEG while the other targets a cell antigen, such as the cancer marker epidermal growth factor receptor (EGFR) or the T cell marker CD3. We used flow cytometry and confocal microscopy to investigate how the addition of BsAb targeting moieties (1) modulates cell targeting, (2) alters particle stealth properties in human blood, and (3) is influenced by the protein corona formed in autologous human plasma. Cancer cell line targeting by EGFR-targeted PEG particles increased as a factor of BsAb density. In the more complex environment of whole human blood, the highest BsAb density examined resulted in a modest 1.48- to 1.52-fold mean increase in association with primary monocytes and granulocytes, respectively. Association with blood phagocytes occurred primarily in the presence of a plasma protein corona, whether PEG particles were targeted or not. Importantly, in fresh human blood, anti-CD3 targeting substantially increased particle delivery to T cells (23.8- and 18.2-fold after 1 and 5 h, respectively), while non-specific uptake by monocytes and granulocytes increased just 1.5-fold at the highest BsAb density examined. In vivo studies will ultimately determine whether the benefits of targeted delivery outweigh the disruption to stealth properties. BsAb-targeted stealth particles have the potential to deliver therapeutics with minimal off-target effects and/or image cells with high specificity.