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Removal of a Single N-Linked Glycan in Human Immunodeficiency Virus Type 1 gp120 Results in an Enhanced Ability To Induce Neutralizing Antibody Responses

Yun Li,¹ Bradley Cleveland,¹ Igor Klots,^2, Bruce Travis,¹ Barbra A. Richardson,³ David Anderson,² David Montefiori,⁴ Patricia Polacino,² and Shiu-Lok Hu^1,2*

Department of Pharmaceutics,¹ Washington National Primate Research Center,² Department of Biostatistics, University of Washington, Seattle, Washington,³ Duke University Medical Center, Durham, North Carolina⁴

Received 3 August 2007/ Accepted 18 October 2007

Glycans on human immunodeficiency virus (HIV) envelope protein play an important role in infection and evasion from host immune responses. To examine the role of specific glycans, we introduced single or multiple mutations into potential N-linked glycosylation sites in hypervariable regions (V1 to V3) of the env gene of HIV type 1 (HIV-1) 89.6. Three mutants tested showed enhanced sensitivity to soluble CD4. Mutant N7 (N197Q) in the carboxy-terminal stem of the V2 loop showed the most pronounced increase in sensitivity to broadly neutralizing antibodies (NtAbs), including those targeting the CD4-binding site (IgG1b12) and the V3 loop (447-52D). This mutant is also sensitive to CD4-induced NtAb 17b in the absence of CD4. Unlike the wild-type (WT) Env, mutant N7 mediates CD4-independent infection in U87-CXCR4 cells. To study the immunogenicity of mutant Env, we immunized pig-tailed macaques with recombinant vaccinia viruses, one expressing SIVmac239 Gag-Pol and the other expressing HIV-1 89.6 Env gp160 in WT or mutant forms. Animals were boosted 14 to 16 months later with simian immunodeficiency virus gag DNA and the cognate gp140 protein before intrarectal challenge with SHIV89.6P-MN. Day-of-challenge sera from animals immunized with mutant N7 Env had significantly higher and broader neutralizing activities than sera from WT Env-immunized animals. Neutralizing activity was observed against SHIV89.6, SHIV89.6P-MN, HIV-1 SF162, and a panel of subtype B primary isolates. Compared to control animals, immunized animals showed significant reduction of plasma viral load and increased survival after challenge, which correlated with prechallenge NtAb titers. These results indicate the potential advantages for glycan modification in vaccine design, although the role of specific glycans requires further examination.

Published ahead of print on 24 October 2007.

Present address: Institute of Medical Primatology, Russian Academy of Medical Sciences, Veseloye 1, Sochi-Adler 354376, Russia.

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