Design and Engineering of Deimmunized Vaccinia Viral Vectors

Abstract

Vaccinia viral (VV) vectors are increasingly used in oncolytic virus therapy and vaccine development for cancer and infectious diseases. However, their effectiveness is hindered by the strong anti-viral immune response induced by the viral vector. In this review, we discuss the strategies to deimmunize vaccinia viral vector. One approach is to mask the virus from the neutralization antibody responses by mapping and eliminating of B-cell epitopes on the viral membrane proteins. The recombinant VVs contain one or more viral glycoproteins with mutations in the neutralizing antibody epitopes, resulting in viral escape from neutralization. In addition, a regulator of complement activation (e.g., CD55) can be expressed on the surface of the virus particle, leading to increased resistance to complement-mediated neutralization.

Keywords: complement; deimmunization; immunogenicity; neutralizing antibody; oncolytic vaccinia virus.

Figure 1

Schematic diagrams for an experimentally driven B cell epitope deletion strategy. A panel of overlapping synthetic peptide fragments spanning the full sequence of H3L viral protein is synthesized. The peptides are then tested for immune recognition, typically using in vitro ELISA with polyclonal anti-vaccinia viral (VV) antibodies. Identified immunogenic peptides are subjected to alanine scanning mutagenesis and retested for immune recognition. Confirmed deimmunizing mutations are then engineered back into the H3L viral proteins and tested for viral packaging, production, stability, and activity. This figure describes the B cell epitope deletion procedure that is conducted in the author’s group [52].

Figure 2

The mechanisms of antibody- and complement-mediated neutralization of virus. Antibody can block cell entry of virus. In addition, antibody can lead to phagocytosis of the virus via Fc–FcR interaction. The complement system is activated primarily by three pathways, including classical pathway, lectin pathway, and alternative pathway. In the classical pathway, viral antigen is recognized by neutralization antibody. The viral antigen–antibody complex induces activation of complement system. Neutralization of viruses by complement occurs owing to different mechanisms. First, virus can form a membrane attach complex (MAC) on the viral envelopes and produce holes of ~100 A diameter in the virus membrane. In addition, opsonization of viral surface with complement can lead to aggregation of viruses as well as phagocytosis of these viruses via a complement receptor (CR) present on the phagocytic cells.