Antigenicity and Immunogenicity of a Synthetic Human Immunodeficiency Virus Type 1 Group M Consensus Envelope Glycoprotein

Abstract

Genetic variation of human immunodeficiency virus (HIV-1) represents a major obstacle for AIDS vaccine development. To decrease the genetic distances between candidate immunogens and field virus strains, we have designed and synthesized an artificial group M consensus env gene (CON6 gene) to be equidistant from contemporary HIV-1 subtypes and recombinants. This novel envelope gene expresses a glycoprotein that binds soluble CD4, utilizes CCR5 but not CXCR4 as a coreceptor, and mediates HIV-1 entry. Key linear, conformational, and glycan-dependent monoclonal antibody epitopes are preserved in CON6, and the glycoprotein is recognized equally well by sera from individuals infected with different HIV-1 subtypes. When used as a DNA vaccine followed by a recombinant vaccinia virus boost in BALB/c mice, CON6 env gp120 and gp140CF elicited gamma interferon-producing T-cell responses that recognized epitopes within overlapping peptide pools from three HIV-1 Env proteins, CON6, MN (subtype B), and Chn19 (subtype C). Sera from guinea pigs immunized with recombinant CON6 Env gp120 and gp140CF glycoproteins weakly neutralized selected HIV-1 primary isolates. Thus, the computer-generated "consensus" env genes are capable of expressing envelope glycoproteins that retain the structural, functional, and immunogenic properties of wild-type HIV-1 envelopes.The high level of genetic variability of HIV-1 poses a major hurdle for AIDS vaccine development. Genetic differences among HIV-1 groups M, N, and O are extensive, ranging from 30 to 50% in the gag and env genes, respectively (14,20,33,35). HIV-1 also frequently recombines among different subtypes to create circulating recombinant forms (CRFs) and novel recombinants (5, 27, 28). To overcome the challenge of HIV-1 diversity, "centralized" HIV-1 genes have been proposed to use in HIV-1 immunogen design. These strategies include using consensus sequences, the most frequent base found in a given position, or ancestral or center-of-the-tree sequences, both modeled from phylogenetic trees (9,10,12,18,23,24). A sequence that is central to all HIV-1 epidemic strains within group M would increase amino acid similarities with contemporary field HIV-1 isolates relative to intersubtype distances and therefore might be useful in a setting where diverse subtypes and recombinants are cocirculating (12). However, because centralized genes are artificially made, it has been of great concern that these genes may not be able to fold into native conformations, perform biological functions of native Env, preserve Env antigenic epitopes, or induce salutary immune responses when used as immunogens. To address these concerns, we synthesized an artificial group M consensus env gene (CON6 gene) and studied its biological, antigenic, and immunological properties. Our studies demonstrated that CON6 proteins are biologically functional and are immunogenic for eliciting immune responses to wild-type HIV-1 strains. MATERIALS AND METHODSExpression of CON6 gp120 and gp140CF proteins by using rVVs. To generate s...

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