Analysis of the human immunodeficiency virus type 1 gp41 membrane proximal external region arrayed on hepatitis B surface antigen particles

Abstract

Vaccine immunogens derived from the envelope glycoproteins of the human immunodeficiency virus type 1 (HIV-1) that elicit broad neutralizing antibodies remain an elusive goal. The highly conserved 30 amino-acid membrane proximal external region (MPER) of HIV gp41 contains the hydrophobic epitopes for two rare HIV-1 broad cross-reactive neutralizing antibodies, 2F5 and 4E10. Both these antibodies possess relatively hydrophobic HCDR3 loops and demonstrate enhanced binding to their epitopes in the context of the native gp160 precursor envelope glycoprotein by the intimate juxtaposition of a lipid membrane. The hepatitis B surface antigen (HBsAg) S1 protein forms nanoparticles that can be utilized both as an immunogenic array of the MPER and to provide the lipid environment needed for enhanced 2F5 and 4E10 binding. We show that recombinant HBsAg particles with MPER (HBsAg-MPER) appended at the C-terminus of the S1 protein are recognized by 2F5 and 4E10 with high affinity compared to positioning the MPER at the N-terminus or the extracellular loop (ECL) of S1. Addition of C-terminal hydrophobic residues derived from the HIV-1 Env transmembrane region further enhances recognition of the MPER by both 2F5 and 4E10. Delipidation of the HBsAg-MPER particles decreases 2F5 and 4E10 binding and subsequent reconstitution with synthetic lipids restores optimal binding. Inoculation of the particles into small animals raised cross-reactive antibodies that recognize both the MPER and HIV-1 gp160 envelope glycoproteins expressed on the cell surface; however, no neutralizing activity could be detected. Prime:Boost immunization of the HBsAg-MPER particles in sequence with HIV envelope glycoprotein proteoliposomes (Env-PLs) did not raise neutralizing antibodies that could be mapped to the MPER region. However, the Env-PLs did raise anti-Env antibodies that had the ability to neutralize selected HIV-1 isolates. The first generation HBsAg-MPER particles represent a unique means to present HIV-1 envelope glycoprotein neutralizing determinants to the immune system.

Hepatitis B Virus Surface Antigen Assembly Function Persists when Entire Transmembrane Domains 1 and 3 Are Replaced by a Heterologous Transmembrane Sequence

“…Although an MPER immunogen is highly desirable, it presents a number of challenges. First, MPER is weakly immunogenic (34). Many successful vaccines depend on particle formation to enhance vaccine potency.…”

“…This method allowed us to express membrane proteins and transmembrane proteins like gp41 on a lipid surface (34). The membraneproximal exposed region of gp41 (MPER) is an important target of broadly reactive neutralizing antibodies against HIV (27).…”

Prolonged exposure of the HIV-1 gp41 membrane proximal region with L669S substitution

“…MPER-specific broadly neutralizing antibodies are rarely made in HIV-1 infection (2-4), but recent studies from our group and others have shown that 2F5-like antibodies responsible for neutralization breadth can be found in ≈0.3% of HIV-1 infected subjects (5), whereas 4E10-like antibodies can be found in ∼3% of HIV-1 positive subjects (6). Vaccination with antigenic envelope constructs expressing 2F5 and 4E10 epitopes has not induced high-titered neutralizing antibodies (7)(8)(9)(10). One hypothesis for the failure of such vaccines to elicit broadly neutralizing antibodies is that the Env epitopes presented to host B cells are not in the correct envelope conformation; for the MPER, this conformation may be the transient, prehairpin gp41 intermediate (11,12).…”

Profiling the Specificity of Neutralizing Antibodies in a Large Panel of Plasmas from Patients Chronically Infected with Human Immunodeficiency Virus Type 1 Subtypes B and C

“…In the few studies reported so far, little or no MPER activity was observed with most HIVpositive (HIV ϩ ) plasmas (3,14,18,35,69). MPER epitopes, including that of 4E10, have been reported to mimic cardiolipin, and as a result, B-cell responses against this region may be regulated by immune tolerance (25), which might also explain the difficulties in formulating vaccine candidates to induce anti-MPER NAbs (26,47,48). However, there have been exceptional cases where relatively high MPER titers were detected in HIV-1 infections (23).…”