Abstract: The present disclosure provides customizable enucleated erythroid cells or enucleated cells that can be engineered to include, on their surface, a loadable exogenous antigen-presenting polypeptide, wherein the loadable exogenous antigen-presenting polypeptide comprises one or more amino acid substitutions. In some embodiments, the one or more amino acid substitutions stabilize the loadable exogenous antigen-presenting polypeptide on the cell surface. In some embodiments, the loadable exogenous antigen-presenting polypeptide is stabilized on the cell surface in the absence of a polypeptide bound to the loadable exogenous antigen-presenting polypeptide. In some embodiments, the loadable exogenous antigen-presenting polypeptide comprises an exogenous displaceable polypeptide bound to the loadable exogenous antigen-presenting polypeptide. In some embodiments, the loadable exogenous antigen-presenting polypeptide is stabilized on the cell surface upon release of the displaceable polypeptide.