Red Blood Cells: Leveraging the Body for the Enhanced Delivery of Biotherapeutics

Red blood cells (RBCs) have been extensively studied as a potential biotherapeutic delivery system for several decades. This research has been prompted by these cells' remarkable properties. RBCs are incredibly tenacious and robust, possessing the high mechanical flexibility needed to flow through the human vasculature for 120 days. Their unusual biconcave shape gives them a high surface-area-to-volume ratio, and the expression of a variety of immunomodulatory markers on the RBC membrane allows for excellent biocompatibility and low immunogenicity. Coupling a therapeutic protein to the RBC surface has the potential to enhance its pharmacokinetics as well as modulate its immune response. The goal of this work was to explore a chemistry-oriented approach to synthesizing RBC-based drug delivery systems. Covalent crosslinking to the RBC membrane is ideal for prolonging the circulation of biotherapeutics with intravascular drug targets. Donor or autologous blood can be modified ex vivo with a method that is rapid, tunable, and cell-tolerated. In Chapter 2, we synthesized an RBC platform that could stably display almost any therapeutic antibody. Our system consisted of an RBC covalently coupled to Protein A (SpA) via a polyethylene glycol (PEG) crosslinker. The antibody was then presented on the RBC surface by SpA binding at its Fc region. In Chapter 3, we directly tethered butyrylcholinesterase (BChE) via PEG to the RBC membrane to develop an improved prophylactic treatment against organophosphate nerve agents. After the synthesis of each RBCPEG-protein construct, we confirmed that the therapeutic was still active once displayed on the surface and performed a series of in vitro assays to assess the impact of engineering on cell health. Finally, in Chapter 4, we began preliminary studies exploring the use of atom-transfer radical polymerization (ATRP) for RBC-biotherapeutic coupling. Our results provide early evidence that chemical conjugation can be a viable approach for RBC-based drug delivery systems. In future work, we plan to use an animal model to test the safety, toxicity, and efficacy of our RBC-biotherapeutic platforms.