Immunogenicity of HIV-1 Vaccines Expressing Chimeric Envelope Glycoproteins on the Surface of Pr55 Gag Virus-Like Particles

Abstract

The HIV-1 envelope glycoprotein (Env) is present on the surface of the virion at a very low density compared to most other enveloped viruses. Substitution of various parts of the stalk domain of Env (gp41) with the corresponding elements from other viral glycoproteins has been shown to increase Env spike density on the cell membrane and surface of virus-like particles (VLPs). In this study, chimeric Env antigens were generated by replacing the transmembrane and cytoplasmic domains of HIV-1 Env with the corresponding regions from the influenza H5 hemagglutinin (HA) (gp140HA2tr) and by replacing the entire gp41 region of Env with the HA2 subunit of HA (gp120HA2). Recombinant DNA and modified vaccinia Ankara (MVA) vaccines expressing HIV-1 subtype C mosaic Gag and gp150 Env or either of the chimeras were generated. Surprisingly, no significant differences were found in the levels of expression of gp150 Env or either of the chimeras on the surface of cells or on Gag VLPs. Differences were, however, observed in the binding of different monoclonal antibodies to the HIV-1 Env. Monoclonal antibodies, which recognized a V1 / V2 quaternary epitope at the tip of the native Env trimer, bound gp150 and gp140HA2tr chimera but failed to bind to the gp120HA2 chimera. Autologous Tier 2 neutralizing antibodies (NAbs) were produced by rabbits inoculated with DNA and MVA vaccines expressing the gp140HA2tr chimera or gp150 Env, but not those immunized with the gp120HA2 Env. These results showed that the addition of an HA2 stalk to HIV-1 gp120 did not improve immunogenicity, but rather that the full-length gp150 was required for optimal presentation of epitopes for the elicitation of a neutralizing antibody response to HIV-1.

Immunogenicity of HIV-1-Based Virus-Like Particles with Increased Incorporation and Stability of Membrane-Bound Env

“…The enhanced incorporation of MMTV-TMCT- and HA-TMCT-modified Env were broadly consistent with the improved incorporation reported when the same substitutions were used with insect-cell-produced HIV-1 VLPs [ 33 ], although the HA-TMCT enhanced incorporation more efficiently in this study. These results also contrasted with a study incorporating similar Env/HA-TMCT constructs into Gag-only VLPs that showed no improvement over wild-type Env [ 105 ]. These differences are probably reflective of the different cell lines and VLP expression vectors used.…”

Assessment of an LSDV-Vectored Vaccine for Heterologous Prime-Boost Immunizations against HIV

“…The expression of the Env and Gag proteins in cells infected with the LSDV vaccine was confirmed by Western blotting and immunofluorescent staining (Figure 2). In vitro expression of Env and Gag has previously been confirmed for the DNA and MVA vaccines [34,36].…”

“…All four human monoclonal antibodies (CAP256 VRC26.08, PGT128, VRC01, and PG9) tested, bound, to some extent, to the Env expressed by LSDVGC5 (Figure 3). The live cell staining of the cells transfected with the DNA vaccine or infected with the MVA vaccine was carried out previously with a larger panel of monoclonal antibodies [34,36]. A summary of the live cell staining results for the Env expressed by all three vaccines (DNA, MVA, and LSDV) is given in Figure 3b.…”

“…With advances in HIV-1 vaccine research, vast improvements have been made in vaccine design to improve the induction of neutralizing antibodies [31,32]; our group has incorporated many of these features into making improved candidate vaccines against HIV-1 [33][34][35][36][37]. The CAP256 superinfecting viral envelope (CAP256.SU) was selected for use in this study as the patient from which the virus was isolated developed broadly neutralizing antibodies (bNAbs) [38].…”

Infection of Chinese Rhesus Monkeys with a Subtype C SHIV Resulted in Attenuated In Vivo Viral Replication Despite Successful Animal-to-Animal Serial Passages

“…Research efforts in South Africa have resulted in the development of a number of candidate HIV-1 vaccines [ 32 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 ] including SAAVI DNA-C2 and SAAVI MVA-C, the only two African-produced candidates ever to have successfully moved from basic research to Phase 1 clinical trials [ 54 , 55 ]. These efforts have also led to the establishment of the Chacma baboon and ChRM as nonhuman primate models for the immunogenicity evaluation of these vaccine candidates [ 32 , 39 , 40 , 43 , 44 , 45 , 56 ].…”