Immunogenic and Antigenic Dominance of a Nonneutralizing Epitope over a Highly Conserved Neutralizing Epitope in the gp41 Envelope Glycoprotein of Human Immunodeficiency Virus Type 1: Its Deletion Leads to a Strong Neutralizing Response

Abstract

The Kennedy peptide, (731)PRGPDRPEGIEEEGGERDRDRS(752), from the cytoplasmic domain of the gp41 transmembrane envelope glycoprotein of HIV-1 contains a conformationally dependent neutralizing epitope (ERDRD) and a linear nonneutralizing epitope (IEEE). No recognized murine T cell epitope is present. The peptide usually stimulates virus-specific antibody, but this is not always neutralizing. Here we show that IEEE (or possibly IEEE plus adjacent sequence) is immunogenically and antigenically dominant over the ERDRD neutralizing epitope. Thus rabbits immunized in a variety of routes, doses, and adjuvants with a chimeric cowpea mosaic virus (CPMV) expressing the Kennedy peptide on its surface (CPMV-HIV/1) synthesized IEEE-specific serum antibody but no ERDRD-specific or HIV-1-neutralizing antibody. To test if this resulted from immunodominance or from a hole in the antibody repertoire, we immunized rabbits with chimera CPMV-HIV/29, which expresses the GERDRDR part of the Kennedy sequence. This chimera readily stimulated ERDRD-specific, neutralizing antibody. In mice the situation was less extreme, but individual animals with low neutralizing titers had a high ratio of IEEE-specific:ERDRD-specific antibody. Data are consistent with immunodominance of IEEE over ERDRD in the Kennedy peptide. IEEE-specific antibody was also antigenically dominant and prevented ERDRD-specific antibody from binding to its epitope and from neutralizing HIV-1. It may be that HIV-1 has evolved a nonneutralizing immunodominant epitope that allows it to possess a neutralizing epitope without suffering the consequences, and this idea is supported by the covariance of both epitope sequences. To our knowledge this is the first example of a defined sequence that controls the activity of an adjacent epitope.

The Membrane-Proximal External Region of the Human Immunodeficiency Virus Type 1 Envelope: Dominant Site of Antibody Neutralization and Target for Vaccine Design

“…CT reactivity. Although it is thought that the CT of gp41 is contained by the viral membrane, there are several MAbs that recognize a hydrophilic region in the so-called "Kennedy epitope" (PRGPDRPEGIEEEGGERDRDRS) at the N terminus of the CT (aa 724 to 745) (29,44). Two possible structures have been proposed for the CT, with each being adopted as part of drastic conformational changes produced by gp41 during viral infection (41,61).…”

“…These have included examples of incorporating membrane into an MPERbased immunogen (134,170,258,264), removing or altering ID epitopes to enhance the Ab response to weakly immunogenic epitopes (44,78,107,210), and various prime-boost strategies to enhance immunogenicity (12,57,90). It is unlikely that a single approach will produce a successful MPER-targeting vaccine; a combination of these approaches may be required.…”

Properties of a neutralizing antibody that recognizes a conformational form of epitope ERDRD in the gp41 C-terminal tail of human immunodeficiency virus type 1

“…Plasmid pCP2-0.51 contains RNA 2, which encodes the two virus coat protein molecules, S and L. The S protein is modified to contain a foreign peptide such that it is expressed on the outer surface of the CPMV chimeric virion. In the present study, chimera CPMV-HIV\1 expresses the peptide ($"PRGPDRPEGIEEEGGERDRDRS(&#, from an external loop of the C-terminal tail of the gp41 transmembrane protein of HIV-1 strain IIIB (Cleveland et al, 2000), and CPMV-HIV\29 expresses (%&GERDRDR(&". Infectious virus was obtained by transfecting leaves of 10-day-old cowpea plants (Vigna unguiculata var. '…”

Evidence against Extracellular Exposure of a Highly Immunogenic Region in the C-Terminal Domain of the Simian Immunodeficiency Virus gp41 Transmembrane Protein

“…The HIR within gp41CTD of SIVmac239 is highly similar in location, if not in sequence, to the immunogenic region of the HIV-1 gp41CTD, the so-called "Kennedy epitope" (13,30,58). It was this high immunogenicity in HIV-1 which led to the proposal of an alternative topology featuring an extracellular loop (14,17,26).…”