HIV-1 Envgp140 trimers elicit neutralizing antibodies without efficient induction of conformational antibodies
Introduction
Despite a variety of vaccine approaches that elicit diverse immune responses, currently no HIV/AIDS vaccine is effective at preventing viral infection [1], [2], [3], [4], [5], [6], [7], [8], [9]. A lack of understanding of the immune correlates for protection is a primary reason for the ineffectiveness of past AIDS vaccines [10]. Previous passive immunization studies demonstrated that sterilizing immunity against simian immunodeficiency virus (SIV) and simian-human immunodeficiency virus (SHIV) infection is possible [11], [12], [13], [14]. However, a successful vaccine against HIV-1 should not only have the capacity to induce HIV-1 specific antibodies, but also to potent cellular immunity to clear virally infected cells [15], [16], [17].
Previous HIV-1/AIDS vaccines utilizing live-attenuated virus, viral vectors, and recombinant subunit proteins have been tested with varying degrees of success (for reviews please see [18], [19], [20], [21]). In the past decade, vaccination with DNA plasmids has offered an alternative strategy for the elicitation of both humoral and cellular immune responses without some of the safety issues associated with live virus or viral vectors [22], [23], [24], [25]. However, the efficient elicitation of immune responses by DNA vaccines in small rodents has not translated into the elicitation of high-titer, protective immunity in non-human primates [16], [26], [27]. Priming the immune system with a DNA plasmid(s), followed by one of a variety of booster inoculations (i.e. viral vectors or recombinant proteins), has proven an effective strategy for eliciting high-titer immune responses to HIV-1 antigens [16], [26].
The role of Env appears critical for the induction of protective immunity in recent AIDS vaccine candidates tested in non-human primates [28], [29]. Inclusion of Env in a multi-component AIDS vaccine resulted in lower viral set points and higher CD4 counts following challenge compared to the same vaccines lacking Env. Envelope on the native virion most likely forms a trimer, although one model suggests that both functional and non-functional trimeric spikes are present on virions. Several vaccine strategies have incorporated an oligomeric/trimeric form of Env in order to elicit cross-reactive immunity that neutralizes viral infection [1], [4], [5], [8], [30], [31], [32], [33], [34], [35], [36], [37], [38]. Soluble, stabilized Env trimers are designed to better mimic the trimeric structure of the envelope on the native virion compared to monomeric immunogens. The goal of trimer immunogen design is to present and preferentially induce conformationally dependent antibodies that recognize epitopes present only on the native virion-associated spikes. Several of these trimeric Env immunogens do elicit significantly slightly higher titers of neutralizing antibodies than monomeric Envgp120 [32], [38], [39], [40], however the breadth of neutralization is still somewhat limited. Often, these oligomeric Env proteins are produced by eliminating the natural cleavage site recognized by cellular proteases [37], [41], [42], [43], which might influence the trimeric structure [4], [5]. The lack of elicited high-titer, broadly reactive neutralizing antibodies by these immunogens may be associated with the elicitation of primarily non-neutralizing antibodies [5], [44], [45], which may because these uncleaved envelopes (1) are in non-native forms or (2) are processed through different cellular pathways than cleaved forms of Env [4], [5], [46], [47].
In this study, soluble, stabilized trimeric Envgp140 molecules were constructed and used as immunogens in a DNA prime/trimerized Envgp140 protein boost regimen to examine if the induced immunity potentially correlates with neutralization. Each trimeric Envgp140 molecule contained the Envgp120 exterior of Env and the ectodomain of Envgp41, stabilized with synthetic trimerization motifs from the T4 bacteriophage fibritin (FT) [Envgp140(FT)] [37]. This motif appears as stable in vitro as the previously described eukaryotic GCN4 stabilization motif [Envgp140(GCN4)] [36], [37]. Even though uncleaved Envgp140 trimers are not yet optimally designed, these proteins did elicit marginally higher neutralizing titers than monomers of Envgp120 [32] and therefore, in this study the goal was to determine whether these elicited neutralizing antibodies correlated with the induction of conformationally dependent antibodies.
Section snippets
Plasmid DNA
The pTR600 eukaryotic expression vector, the monomeric, soluble Envgp120 or the FT stabilized Envgp140 from the isolate, YU-2 (accession # M93258), have been previously described [32]. Briefly, the plasmids expressing Envgp120 contain a gene segment expressing the entire ectodomain of gp120 (nt 1–1500). The Envgp140 plasmid expresses a protein representing the entire ectodomains from gp120 and gp41, which was stabilized by the addition of the synthetic trimerization domain derived from the T4
Elicitation of anti-Env antibodies in vaccinated mice
Mice (BALB/c) were vaccinated via gene gun on Day 1 and week 4 with either high dose DNA (2.0 μg) or low dose DNA (0.2 μg) plasmids. Regardless if the mice were primed with monomeric Envgp120 or trimeric Envgp140 or if the envelopes were conjugated to mC3d3, each mouse had anti-Env IgG titers after the second DNA plasmid inoculation (week 6), which rose following a boost of recombinant Envgp140 (Fig. 2). Mice vaccinated with a high dose of DNA expressing any of the Env immunogens had anti-Env
Discussion
In this study, several vaccine strategies were combined to elicit anti-Env immune responses. Mice were vaccinated with two doses of DNA plasmid expressing soluble forms of Env followed by a booster inoculation of a purified, recombinant, trimerized Envgp140 protein. Mice were primed with either a high dose of DNA (2.0 μg) or a low dose of DNA (0.2 μg), expressing one of two forms of envelope (monomeric gp120 or trimeric gp140). Additional groups of mice were vaccinated with DNA expressing
References (80)
- et al.
Selective recognition of oligomeric HIV-1 primary isolate envelope glycoproteins by potently neutralizing ligands requires efficient precursor cleavage
Virology
(2005) - et al.
DNA vaccines for viral infections: basic studies and applications
Adv Virus Res
(2000) - et al.
A new generation of HIV vaccines
Trends Mol Med
(2002) Expression, purification, and characterization of recombinant HIV gp140. The gp41 ectodomain of HIV or simian immunodeficiency virus is sufficient to maintain the retroviral envelope glycoprotein as a trimer
J Biol Chem
(2001)- et al.
Expanded breadth of virus neutralization after immunization with a multiclade envelope HIV vaccine candidate
Vaccine
(2005) - et al.
Endoproteolytic cleavage of gp160 is required for the activation of human immunodeficiency virus
Cell
(1988) - et al.
C3d enhancement of neutralizing antibodies to measles hemagglutinin
Vaccine
(2001) - et al.
Particle-mediated nucleic acid immunization
J Biotechnol
(1996) - et al.
Gene gun based nucleic acid immunization eliciting of humoral and cytotoxic T lymphocyte response following epidermal delivery of nanogram quantitation of DNA
Vaccine
(1995) - et al.
Studies on antibody responses following neonatal immunization with influenza hemagglutinin DNA or protein
Virology
(1999)
Analysis of the neutralizing antibody response elicited in rabbits by repeated inoculation with trimeric HIV-1 envelope glycoproteins
Virology
Allocation of helper T-cell epitope immunodominance according to three-dimensional structure in the human immunodeficiency virus type I envelope glycoprotein gp120
J Biol Chem
Comparative analysis of immune responses and cytokine profiles elicited in rabbits by the combined use of recombinant fowlpox viruses, plasmids and virus-like particles in prime-boost vaccination protocols against SHIV
Vaccine
Independent but not synergistic enhancement to the immunogenicity of DNA vaccine expressing HIV-1 gp120 glycoprotein by codon optimization and C3d fusion
Vaccine
Induction of heterosubtypic immunity to influenza A virus using a DNA vaccine expressing hemagglutinin-C3d fusion proteins
Vaccine
Evaluating the immunogenicity of a disulfide-stabilized, cleaved, trimeric form of the envelope glycoprotein complex of human immunodeficiency virus type 1
J Virol
DNA vaccines, combining form of antigen and method of delivery to raise a spectrum of IFN-gamma and IL-4-producing CD4+ and CD8+ T cells
J Immunol
DNA vaccines: influenza virus challenge of a Th2/Tc2 immune response results in a Th2/Tc1 response in the lung
J Virol
Soluble mimetics of human immunodeficiency virus type 1 viral spikes produced by replacement of the native trimerization domain with a heterologous trimerization motif: characterization and ligand binding analysis
J Virol
Contribution of virus-like particles to the immunogenicity of human immunodeficiency virus type 1 Gag-derived vaccines in mice
J Virol
Modifications that stabilize human immunodeficiency virus envelope glycoprotein trimers in solution
J Virol
The antigenic structure of the HIV gp120 envelope glycoprotein
Nature
Correlates of immune protection in HIV-1 infection: what we know, what we don’t know, what we should know
Nat Med
Protection of macaques against vaginal transmission of pathogenic HIV-1/SIV chimeric virus by passive infusion of neutralizing antibodies
Nat Med
Neutralizing antibody directed against the HIV-1 envelope glycoprotein can completely block HIV-1/SIV chimeric virus infections of macaque monkeys
Nat Med
Pre- and postexposure protection against human immunodeficiency virus type 1 infection mediated by a monoclonal antibody
J Infect Dis
Prevention of HIV-1 infection in chimpanzees by gp120 V3 domain-specific monoclonal antibody
Nature
Control of a mucosal challenge and prevention of AIDS by a multiprotein DNA/MVA vaccine
Science
New hope for an AIDS vaccine
Nat Rev Immunol
Identifying epitopes of HIV-1 that induce protective antibodies
Nat Rev Immunol
Current prospects for the development of a therapeutic vaccine for the treatment of HIV type 1 infection
AIDS Res Hum Retroviruses
Application of the polyvalent approach to HIV-1 vaccine development
Curr Drug Targets Infect Disord
HIV vaccine rationale, design and testing
Curr HIV Res
Predictive value of primate models for AIDS
AIDS Rev
DNA vaccines for immunodeficiency viruses
Aids
DNA vaccines: basic mechanism and immune responses (Review)
Int J Mol Med
DNA vaccines. Mechanisms for generation of immune responses
Adv Exp Med Biol
HIV vaccine design and the neutralizing antibody problem
Nat Immunol
Heterologous envelope immunogens contribute to AIDS vaccine protection in rhesus macaques
J Virol
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2016, Veterinary Immunology and ImmunopathologyCitation Excerpt :Unfortunately, there was a lack of correlation between nAb titer and antibody avidity. This phenomenon has already been observed in studies on measles and HIV vaccines (Bower et al., 2006; Kemp et al., 2012), indicating that the relationship between nAb titer and antibody avidity may be independent of their protective ability. For numerous human pathogenic viruses, including measles virus, infected individuals or vaccine failures could be distinguished from vaccinated individuals and accurate estimations of vaccination time could be performed based on levels of antibody avidity (Paunio et al., 2000; Kontio et al., 2012).
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2010, VaccineCitation Excerpt :There have been reports of a broad neutralizing response following vaccination of oligomeric forms of gp140. Unfortunately, the reported breadth of activity consisted of mostly low serum titers, often with titers of <1:100, and not all gp140 trimeric Env preparations induce significant titers of neutralizing Abs able to recognize conformational epitopes [21]. Additionally, virus-like particles (VLPs) bearing disulfide-stabilized functional trimers (SOS-VLPs) and cleavage-site mutated Env VLPs predominantly induced Ab responses against non-functional forms of Env and not against the trimeric Env [22].
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2009, VirologyCitation Excerpt :Immunization of rabbits with the gp140(-)GCN fusion protein elicited neutralizing antibodies of greater potency and breath than did either gp120 or solid-phase proteoliposomes containing a cleavage-defective Env (Grundner et al., 2005). A separate immunization study using mice showed that the gp140(-)T4F fusion was only marginally more effective than gp120 at eliciting neutralizing antibodies (Bower et al., 2006). Another trimerization domain that has been fused to gp140 is the catalytic chain of aspartate transcarbamoylase (ATCase).
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2007, VaccineCitation Excerpt :Thus, gp140 was thought to be a better vaccine immunogen, as it contains the entire ectodomain of HIV-1 Env and can be secreted from expressing cells. Several vaccine strategies attempted to elicit cross-reactive antibodies by incorporating an oligomeric/trimeric form of gp140 [35–40]. Immunogenicity comparison between gp120 and gp140 showed that sera raised by gp140 exhibited improved cross-reactivity to heterologous Env proteins and greater neutralizing activities compared to what to be raised by gp120 [41].
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