Covalent Linkage to β2-Microglobulin Enhances the MHC Stability and Antigenicity of Suboptimal CTL Epitopes

Many CTL epitopes of clinical importance, particularly those derived from tumor Ags, display relatively poor MHC binding affinity and stability. Because in vivo immunogenicity, and thus the efficacy of peptide-based vaccines, is thought to be determined by MHC/peptide complex stability, there is a need to develop a simple strategy for enhancing the binding of suboptimal epitopes. Toward this goal, the ability to enhance suboptimal peptides through covalent linkage to β 2 -microglobulin (β 2 m) was explored. Two suboptimal variants of a high-affinity D b -restricted influenza nucleoprotein peptide were covalently linked, via a polypeptide spacer, to the amino terminus of human β 2 m and the recombinant fusion proteins expressed in Escherichia coli . When compared with their uncoupled counterparts, the β 2 m-linked epitopes display enhanced MHC stabilization and antigenicity. Thus, tethering epitopes to β 2 m provides a simple method for augmenting the biological activity of suboptimal peptides and could be useful in the design of peptide-based vaccines or immunotherapeutics.