A comparative immunogenicity study of HIV-1 virus-like particles bearing various forms of envelope proteins, particles bearing no envelope and soluble monomeric gp120

Abstract

To assess the potential of native Envelope glycoprotein (Env) trimers as neutralizing antibody vaccines, we immunized guinea pigs with three types of VLPs and soluble gp120. Particles included "SOS-VLPs" (bearing disulfide-shackled functional trimers), "UNC-VLPs" (bearing uncleaved nonfunctional Env) and "naked VLPs" (bearing no Env). The SOS-VLPs were found to have a density of about 27 native trimers per particle, approximately twice that of live inactivated HIV-1 preparations. As immunogens, UNC- and SOS-VLP rapidly elicited anti-gp120 antibodies focused on the V3 loop and the gp120 coreceptor binding site. Reactivity to the gp41 immunodominant domain was absent in SOS-VLP sera, presumably because gp120-gp41 association is stabilized, effectively covering this epitope. Gp120-immune sera reacted with the receptor binding sites of gp120 and were less focused on the V3 loop. Some Env-VLP sera neutralized primary isolates at modest titers. The measurement of neutralization was found to be affected by the cell lines used. Depending on the assay particulars, non-Env specific antibodies in VLP sera could enhance infection, or nonspecifically neutralize. However, a neutralization assay using TZM-BL cells was essentially clear of these effects. We also describe a native trimer binding assay to confirm neutralization activity in a manner that completely eliminates nonspecific effects. Overall, our data suggests that Env-VLP sera were primarily focused on nonfunctional forms of Env on VLP surfaces, possibly gp120/gp41 monomers and not the trimers. Therefore, to make progress toward a more effective VLP-based vaccine, we will need to find ways to refocus the attention of B cells on native trimers.

Intraprotomer masking of third variable loop (V3) epitopes by the first and second variable loops (V1V2) within the native HIV-1 envelope glycoprotein trimer

“…An alternative approach of measuring mAb binding to Env-expressing cells could potentially be complicated not only by the presence of inactive homotrimers of each mutant construct, but also by other nonfunctional forms of Env that are likely expressed on the transfected cells. These include trimers of uncleaved gp160 as well as gp120/gp41 monomers, which have been reported on virus-like particles and infectious virions (31)(32)(33) and found to display different patterns of epitope exposure compared with the correctly processed functional trimers (34)(35)(36).…”

Antibodies Targeting the Envelope of HIV-1

“…V3 Abs are present in essentially all infected individuals (91), and V3 Abs have been elicited by several types of vaccines (4,92,93). Moreover, the first demonstration of the successful use of "reverse vaccinology," i.e., the design of vaccines based on epitopes recognized by biologically active mAbs, was achieved using V3-scaffold immunogens which targeted the immune response to this single epitope of the HIV envelope.…”

DNA prime-protein boost using subtype consensus Env was effective in eliciting neutralizing antibody responses against subtype BC HIV-1 viruses circulating in China

“…We also chose to use a pseudotyped virus-based competitive binding assay to examine the specificity of antibodies capable of binding to the important gp120 epitopes on the HIV-1 viral envelope spike as previously reported, 9,19,20 with the hope of determining the specificity differences between antibodies elicited by protein alone or DNA prime-protein boost immunization approaches. Previously, we reported that DNA prime-protein boost could induce improved antibody responses targeting the CD4bs, as such sera could compete well against the broad neutralizing mAb, b12 (Vaine, Wang et al, 2008;Vaine, Wang et al, 2010).…”

“…Competitive binding assays were performed as previously described 20,28 with minor modifications. Pseudovirions bearing the JR-FL Envelope and Vesicular Stomatitis Virus (VSV) glycoprotein were produced with the pSG3…”