Gene replacement is a popular application for mRNA. Many proteins cannot be replaced by exogenous protein delivery, for example, if they are intracellular, membrane bound, or post translationally modified or processed. Intracellular expression from mRNA dramatically expands the number of indications that could potentially be treated by protein replacement. Human erythropoietin (EPO) protein is a secreted protein that is easily measured in serum by enzyme-linked immunosorbent assay. EPO stimulates red blood cell creation, which can be measured using a hematocrit assay. EPO mRNA is available to model your secreted protein.