Engineering Novel Functionality into Red Blood Cells

The red blood cell (erythrocyte) has a well-characterised life cycle and biophysical properties that make them the ideal vehicle for therapeutic use; they are biocompatible, biodegradable, are already designed to traverse the vascular system and lack nuclei. Research to date on the use of erythrocytes as cellular delivery agents has generally focused on loading mature erythrocytes with drugs, encapsulation using isolated erythrocyte membranes or functionalization of the red cell surface, alterations that can be detrimental to the biophysical properties of the erythrocyte.

Our approach is to use an ex vivo erythroid culture system that allows us to culture immature erythrocytes (reticulocytes) from either CD34+ cells isolated from peripheral blood or alternatively by using novel human immortalised erythroid cell lines. We have shown that these erythroid cells can be manipulated by altering their protein expression during erythroid development to engineer erythrocytes with desirable properties.

To utilize the erythrocyte as an effective novel cellular chassis, requires a better understanding of membrane assembly and the rules for the introduction of exogenous membrane proteins.  We have determined when many key membrane proteins in the erythroid membrane assemble, and have overexpressed 9 selected endogenous and exogenous single and multipass membrane proteins. These exhibited a wide variation in the level of membrane expression. We are now engaged in a second phase of design to increase protein retention by reducing loss of proteins due to remodelling during differentiation and enucleation. To achieve this we are altering protein sorting and attachment to the underlying cytoskeleton.  The eventual goal is to develop a “human red blood cell engineering” toolkit to manipulate erythrocytes during their development to obtain novel features and characteristics.