An oligosaccharide-based HIV-1 2G12 mimotope vaccine induces carbohydrate-specific antibodies that fail to neutralize HIV-1 virions.

The conserved oligomannose epitope, Man(9)GlcNAc(2), recognized by the broadly neutralizing human mAb 2G12 is an attractive prophylactic vaccine candidate for the prevention of HIV-1 infection. We recently reported total chemical synthesis of a series of glycopeptides incorporating one to three copies of Man(9)GlcNAc(2) coupled to a cyclic peptide scaffold. Surface plasmon resonance studies showed that divalent and trivalent, but not monovalent, compounds were capable of binding 2G12. To test the efficacy of the divalent glycopeptide as an immunogen capable of inducing a 2G12-like neutralizing antibody response, we covalently coupled the molecule to a powerful immune-stimulating protein carrier and evaluated immunogenicity of the conjugate in two animal species. We used a differential immunoassay to demonstrate induction of high levels of carbohydrate-specific antibodies; however, these antibodies showed poor recognition of recombinant gp160 and failed to neutralize a panel of viral isolates in entry-based neutralization assays. To ascertain whether antibodies produced during natural infection could recognize the mimetics, we screened a panel of HIV-1-positive and -negative sera for binding to gp120 and the synthetic antigens. We present evidence from both direct and competitive binding assays that no significant recognition of the glycopeptides was observed, although certain sera did contain antibodies that could compete with 2G12 for binding to recombinant gp120.

HIV type 1 vaccines for worldwide use: predicting in-clade and cross-clade breadth of immune responses.

One of the greatest challenges in HIV vaccine development is accommodating the worldwide sequence diversity of the HIV-1 virus. To understand how viral sequence diversity may affect the potential breadth of HIV-1 vaccines designed to elicit antiviral T cell immunity, we have developed novel approaches to assess sequence conservation at the amino acid level, where vaccine effects are exerted. Taking each sequence from the LANL 2004 amino acid alignments as a potential vaccine or as a challenge virus, all pairwise combinations of sequences were evaluated by two methods: first, a traditional comparison of aligned sequences, and second, by a new walking 9-mer algorithm chosen to emphasize the typical length of an MHC-I epitope. The rules for comparing mismatched 9-mer pairs between vaccine and challenge sequences were empirically deduced from an experiment on Nef-specific CD8 epitopes and the viral sequences from naturally HIV-1-infected patients. Results were weighted such that each clade contributed in proportion to its global prevalence. Cross-clade breadth of response is best maintained for vaccines encoding Pol and Gag, while commonly proposed Env- and Tat-based vaccines would be more clade sensitive. We evaluated the additional breadth that could be expected from multiclade vaccines including consensus and ancestral sequences. For more diverse proteins, adding a second strain can add a significant increase in breadth, although for three or more strains the intrinsic diversity of the protein leads to diminishing improvement.