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128 Immunogenicity of Conjugated HIV Gp120 and Env 2-3 in Mice
L. C. Paoletti*1 and R. C. Kennedy2
1Brigham & Women’s Hosp., Harvard Med. Sch, Boston, MA, USA and 2Texas Tech Univ. Hlth. Sci. Ctr., Lubbock, TX, USA
Background: HIV gp120 has been tested in human clinical trials as a stand-alone vaccine or as a secondary immunogen in a prime-boost strategy. Compared with other viral subunits, monomeric gp120 preparations are weak immunogens as multiple, high concentration doses are necessary to elicit neutralizing antibody. We hypothesized that covalent coupling technology successful in generating efficacious bacterial polysaccharide-protein vaccines would improve the immunogenicity of HIV gp120 and functional activity of elicited murine serum.
Methods: We created conjugate vaccines by coupling tetanus toxoid (TT), gp120, and/or env2-3 to oxidized group B streptococcal type III polysaccharide (III) by reductive amination. Another construct linked TT directly to periodate-oxidized gp120 (gp120ox-TT). Size-exclusion chromatography revealed the formation of polymers larger than those of the uncoupled proteins after conjugation. CD4+ binding capacity and immunogenicity of 4 conjugated and 4 unconjugated vaccines were evaluated in mice. Neutralizing activity of elicited antibody against clade B isolates was measured.
Results: None of the conjugate preparations containing gp120 or env2-3 bound CD4+ T cells. Vaccines (3- to 5-mug gp120/env2-3/doses with Quil A adjuvant) were administered I.P. to Balb/c mice, a strain known to respond weakly to HIV gp120/gp160. Geometric mean titer (GMT) of gp120-specific IgG in serum from mice that received env2-3-TT-III or env2-3-gp120-TT-III conjugates rose from 50 before to 3,031 and 4,756, respectively, after vaccination. Peak GMT of gp120-specific IgG in serum from mice given 3 doses of a gp120-TT-III was 173; 668 for those given gp120ox-TT. The gp120-specific GMTs in serum from mice given a mixture of gp120, TT, and III, III-TT, uncoupled gp120, or env2-3 were 50, 50, 79, and 794, respectively. Pooled immune serum diluted 1:20 from mice given env-gp120-TT-III vaccine inhibited HIV-1MN infection of SupT1 cells and, with human PBMC as target cells, demonstrated neutralizing activity against a primary isolate of HIV-1 (B/B) infection but none against primary HIV-1 isolates from clades A, C, D, and E. In contrast, serum from mice given uncoupled gp120 or env2-3 did not exhibit neutralizing activity.
Conclusions: Gp120-specific IgG with neutralizing activity against laboratory and primary clade B HIV is achievable with conjugate vaccines containing gp120/env2-3, III, and TT. Such conjugates could reduce the amount of HIV antigen required to elicit neutralizing antibody and act as combination vaccines in the prime-boost strategy.
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