Alterations in the Immunogenic Properties of Soluble Trimeric Human Immunodeficiency Virus Type 1 Envelope Proteins Induced by Deletion or Heterologous Substitutions of the V1 Loop

Abstract

HIV-1 gp140 envelope immunogens express conserved epitopes that are targeted by broadly cross-reactive neutralizing antibodies, but they fail to elicit similar antibodies upon immunization. The poor immunogenicity of conserved epitopes on gp140 could be linked to the high immunogenicity of variable Env regions on such constructs. Previous studies have shown that the first hypervariable region (V1 loop) is immunogenic on soluble gp140s but elicits type-specific antibodies. To address issues related to the high immunogenicity of the V1 loop, two conceptually opposite approaches were tested. In the first approach, we eliminated the V1 loop from our gp140 construct and examined how V1 deletion altered the immunogenic properties of other Env regions. In the second approach, we took advantage of the high immunogenicity of the V1 loop and engrafted four diverse V1 loops onto a common gp140 Env "scaffold." These four scaffolds were used as a cocktail of immunogens to elicit diverse anti-V1 antibodies, under the hypothesis that eliciting diverse anti-V1 antibodies would expand the neutralizing breadth of immune sera. Our study indicates that three of four heterologous V1 loops were immunogenic on the common Env backbone "scaffold," but heterologous anti-V1 neutralizing responses were observed in only one case. Both types of V1 modification dampened the immunogenicity of the V3 loop, differentially altered the immunogenicity of the transmembrane gp41 subunit, and altered the relative immunogenicities of unknown Env regions, including potentially the CD4-binding site (CD4-bs) and trimerspecific targets, which elicited cross-reactive neutralizing antibodies but of limited breadth.An effective vaccine against human immunodeficiency virus type 1 (HIV-1) will need to incorporate an envelope-derived immunogen capable of eliciting potent and broadly cross-reactive neutralizing antibody responses against diverse primary HIV-1 isolates. The target of anti-HIV neutralizing antibodies (NAbs), the viral envelope (Env) glycoprotein, is expressed as a single transmembrane polypeptide precursor (gp160) that is glycosylated and cleaved into an extracellular subunit (gp120) and a transmembrane subunit (gp41) during intracellular processing (10,20,21,54). The functional Env form on virion surfaces is a trimer composed of three noncovalently associated gp120-gp41 heterodimers. Soluble forms of the trimeric Env have been generated by introducing stop codons immediately upstream of the transmembrane domain of gp41. These constructs are commonly referred to as gp140 proteins and have been tested extensively as immunogens to elicit anti-HIV-1 NAbs. Soluble gp140s express epitopes that are targets of NAbs, including cross-reactive NAbs such as b12, 4E10, and 2G12 (5,17,34,45,47,49,50,52,57). Immunization with gp140 immunogens nonetheless does not result in a broadly cross-reactive neutralizing antibody response (2,3,17,18,26,56,58).Epitope mapping analyses of the Abs elicited by soluble trimeric gp140 immunogens revealed that a large fraction of...

Engineering, Expression, Purification, and Characterization of Stable Clade A/B Recombinant Soluble Heterotrimeric gp140 Proteins

“…Similarly to what we observed for the clade A Envs, the immunogenicity of the V2 loop of the SF162 gp140 was poor. In accordance with our previous reports (15,20), the V1 loop of SF162 was immunogenic in the context of SF162 gp140 homotrimers. The association of SF162 gp140 with the clade A gp140s into heterotrimeric conformations did not alter the immunogenicity of the SF162 V1 loop.…”

Antigenicity and Immunogenicity of Transmitted/Founder, Consensus, and Chronic Envelope Glycoproteins of Human Immunodeficiency Virus Type 1

“…The findings we present here are based on using gp140 Envs that may have incremental immunological advantages over gp120 (2,34,70), although gp120 is easier to produce and so historically has been used in human trials (62,71,72). In several studies, stable soluble trimeric HIV-1 Envs have elicited more potent neutralizing antibodies compared to gp120s, but still of limited breadth (70,73).…”

“…In several studies, stable soluble trimeric HIV-1 Envs have elicited more potent neutralizing antibodies compared to gp120s, but still of limited breadth (70,73). Stable, rigorously homogeneous trimers that have antigenic properties markedly different from those of monomeric gp120 induced more potent neutralizing antibodies than those elicited by the corresponding gp120 monomers; however, antibodies induced by such stable trimers also have very limited neutralizing potency and breadth (73,74).…”

Longer V1V2 Region with Increased Number of Potential N-Linked Glycosylation Sites in the HIV-1 Envelope Glycoprotein Protects against HIV-Specific Neutralizing Antibodies

“…Results from earlier studies do, however, imply a direct role for the V1V2 loop in the resistance to neutralizing antibodies. Replacement of the V1V2 loop of neutralization-sensitive T cell line-adapted HIV-1 strains or highly neutralization-sensitive tier 1 viruses, such as SF162 (12,13,34,37), with the V1V2 loop of a more neutralization-resistant virus resulted in less neutralization-sensitive chimeric viruses. In our present study, we used primary HIV-1 variants that are representative of the viruses that occur in human infection (16).…”

“…In particular, the length and glycosylation characteristics of the V1V2 loop seem to play a role in resistance against neutralizing antibodies (8,9,10,33,41,42,43,46,49,52), possibly by shielding underlying regions of Env from antibody recognition (18, 37) and, especially, in the protection against anti-V3 and anti-CD4-binding site antibodies (12,30,37,43).…”