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Crooks E.T.,San Diego Biomedical Research Institute | Tong T.,San Diego Biomedical Research Institute | Chakrabarti B.,Scripps Research Institute | Chakrabarti B.,Translational Health Science and Technology Institute | And 26 more authors.
PLoS Pathogens | Year: 2015

Eliciting broad tier 2 neutralizing antibodies (nAbs) is a major goal of HIV-1 vaccine research. Here we investigated the ability of native, membrane-expressed JR-FL Env trimers to elicit nAbs. Unusually potent nAb titers developed in 2 of 8 rabbits immunized with virus-like particles (VLPs) expressing trimers (trimer VLP sera) and in 1 of 20 rabbits immunized with DNA expressing native Env trimer, followed by a protein boost (DNA trimer sera). All 3 sera neutralized via quaternary epitopes and exploited natural gaps in the glycan defenses of the second conserved region of JR-FL gp120. Specifically, trimer VLP sera took advantage of the unusual absence of a glycan at residue 197 (present in 98.7% of Envs). Intriguingly, removing the N197 glycan (with no loss of tier 2 phenotype) rendered 50% or 16.7% (n = 18) of clade B tier 2 isolates sensitive to the two trimer VLP sera, showing broad neutralization via the surface masked by the N197 glycan. Neutralizing sera targeted epitopes that overlap with the CD4 binding site, consistent with the role of the N197 glycan in a putative “glycan fence” that limits access to this region. A bioinformatics analysis suggested shared features of one of the trimer VLP sera and monoclonal antibody PG9, consistent with its trimer-dependency. The neutralizing DNA trimer serum took advantage of the absence of a glycan at residue 230, also proximal to the CD4 binding site and suggesting an epitope similar to that of monoclonal antibody 8ANC195, albeit lacking tier 2 breadth. Taken together, our data show for the first time that strain-specific holes in the glycan fence can allow the development of tier 2 neutralizing antibodies to native spikes. Moreover, cross-neutralization can occur in the absence of protecting glycan. Overall, our observations provide new insights that may inform the future development of a neutralizing antibody vaccine.

Vojnov L.,University of Wisconsin - Madison | Bean A.T.,University of Wisconsin - Madison | Peterson E.J.,Wisconsin National Primate Research Center | Chiuchiolo M.J.,Design and Development Laboratory | And 10 more authors.
Vaccine | Year: 2011

The goals of a T cell-based vaccine for HIV are to reduce viral peak and setpoint and prevent transmission. While it has been relatively straightforward to induce CD8 + T cell responses against immunodominant T cell epitopes, it has been more difficult to broaden the vaccine-induced CD8 + T cell response against subdominant T cell epitopes. Additionally, vaccine regimens to induce CD4 + T cell responses have been studied only in limited settings. In this study, we sought to elicit CD8 + T cells against subdominant epitopes and CD4 + T cells using various novel and well-established vaccine strategies. We vaccinated three Mamu-A*01 + animals with five Mamu-A*01-restricted subdominant SIV-specific CD8 + T cell epitopes. All three vaccinated animals made high frequency responses against the Mamu-A*01-restricted Env TL9 epitope with one animal making a low frequency CD8 + T cell response against the Pol LV10 epitope. We also induced SIV-specific CD4 + T cells against several MHC class II DRBw*606-restricted epitopes. Electroporated DNA with pIL-12 followed by a rAd5 boost was the most immunogenic vaccine strategy. We induced responses against all three Mamu-DRB*w606-restricted CD4 epitopes in the vaccine after the DNA prime. Ad5 vaccination further boosted these responses. Although we successfully elicited several robust epitope-specific CD4 + T cell responses, vaccination with subdominant MHC class I epitopes elicited few detectable CD8 + T cell responses. Broadening the CD8 + T cell response against subdominant MHC class I epitopes was, therefore, more difficult than we initially anticipated. © 2011 Elsevier Ltd.

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