Protect, Modify, Deprotect (PMD): A strategy for creating vaccines to elicit antibodies targeting a specific epitope
In creating vaccines against infectious agents, there is often a desire to direct an immune response toward a particular conformational epitope on an antigen. We present a method, called Protect, Modify, Deprotect (PMD), to generate immunogenic proteins aimed to direct a vaccine-induced antibody response toward an epitope defined by a specific monoclonal antibody (mAb). The mAb is used to protect the target epitope on the protein. Then, the remaining exposed surfaces of the protein are modified to render them non-immunogenic. Finally, the epitope is deprotected by removal of the mAb. The resultant protein is modified at surfaces other than the target epitope. We validate PMD using the well-characterized antigen, hen egg white lysozyme (HEWL). Then, we demonstrate the utility of PMD using influenza virus hemagglutinin (HA). Specifically, we use a mAb to protect a highly conserved epitope on the stem domain of HA. Exposed surface amines are then modified by introducing short polyethylene glycol (PEG) chains. The resultant antigen shows markedly reduced binding to mAbs that target the variable head region of HA, while maintaining binding to mAbs at the epitope of interest in the stem region. This antigenic preference is also observed with yeast cells displaying antibody fragments. Antisera from guinea pigs immunized with the PMD-modified HA show increased cross-reactivity with HAs from other influenza strains, as compared to antisera obtained with unmodified HA trimers. PMD has the potential to direct an antibody response at high-resolution and could be used in combination with other such strategies. There are many attractive targets for the application of PMD.