Repertoire of Epitopes Recognized by Serum IgG from Humans Vaccinated with Herpes Simplex Virus 2 Glycoprotein D

Abstract

). The vaccine consisted of a soluble form of herpes simplex virus 2 (HSV-2) glycoprotein D (gD2) with adjuvant. The goal of the current study was to examine the composition of the humoral response to gD2 within a selected subset of vaccinated individuals. Serum samples from 30 vaccine recipients were selected based upon relative enzyme-linked immunosorbent assay (ELISA) titers against gD2; 10 samples had high titers, 10 had medium titers, and the remaining 10 had low ELISA titers. We employed a novel, biosensor-based monoclonal antibody (MAb)-blocking assay to determine whether gD2 vaccination elicited IgG responses against epitopes overlapping those of well-characterized MAbs. Importantly, IgGs from the majority of gD2-immunized subjects competed for gD binding with four antigenically distinct virus-neutralizing MAbs (MC2, MC5, MC23, and DL11). Screening of patient IgGs against overlapping peptides spanning the gD2 ectodomain revealed that about half of the samples contained antibodies against linear epitopes within the N and C termini of gD2. We found that the virus-neutralizing abilities of the 10 most potent samples correlated with overall gD-binding activity and to an even greater extent with the combined content of IgGs against the epitopes of MAbs MC2, MC5, MC23, and DL11. This suggests that optimal virus-neutralizing activity is achieved by strong and balanced responses to the four major discontinuous neutralizing epitopes of gD2. IMPORTANCESeveral herpes simplex virus 2 (HSV-2) subunit vaccine studies have been conducted in human subjects using a recombinant form of HSV-2 glycoprotein D (gD2). Although several distinct, well-characterized virus-neutralizing epitopes on gD2 are targeted by murine monoclonal antibodies, it is not known whether the same epitopes are targeted by the humoral response to gD2 in humans. We have developed a novel, biosensor-based competition assay to directly address this important question. Using this approach, we identified epitopes that elicit strong humoral responses in humans, as well as other epitopes that elicit much weaker responses. These data provide new insight into the human response to known neutralizing gD2 epitopes and reveal characteristics of this response that may guide future vaccine development.

Patient-Specific Neutralizing Antibody Responses to Herpes Simplex Virus Are Attributed to Epitopes on gD, gB, or Both and Can Be Type Specific

“…A recent vaccine trial using gD as the sole immunogen failed to protect doubly seronegative women against genital HSV-2 disease but did show some efficacy against HSV-1 (7,32,33). In 10 samples with the most potent neutralizing activity, we found that the strongest correlates of neutralization were the overall gD-specific IgG content, and the combined response to the four major gD epitopes (34). These data suggest that optimal virus neutralization, and possibly protection, would be achieved by strong and balanced responses to the major neutralizing epitopes of gD.…”

“…We also included the non-neutralizing MAb MC14, which significantly enhances neutralization by MAb MC2 (36). In two previous studies of either gD-vaccinated subjects (34) or naturally infected people (35), IgGs from all samples blocked key conformational anti-gD epitopes (MC23, DL11, MC2, and MC5), and yet none blocked binding to linear epitopes (1D3 and MC14). In the present study, all nine sera in the recurrent group blocked the binding of MC23, DL11, and MC5 above a 20% threshold (Fig.…”

“…Experiments were performed at room temperature using either purified sample IgG on a Biacore 3000 biosensor at 25°C as described previously (34,35) or serum samples on an Octet RED96 system (Pall ForteBio) at 30°C (45). For the Octet analysis, we used SA (streptavidin) biosensors and kinetics buffer (phosphate-buffered saline, 0.1% bovine serum albumin, 0.02% Tween) in all experiments.…”

Dissection of the Antibody Response against Herpes Simplex Virus Glycoproteins in Naturally Infected Humans

“…4B). We used an arbitrary cutoff point of 20% in scoring samples positive for blocking (45). Surprisingly, none of the 10 IgGs blocked MAbs 1D3 or MC14 (Fig.…”

“…To characterize the responses to these six gD epitopes in naturally infected individuals, we used a protein-binding competition assay using surface plasmon resonance/biosensor (8,44,45). The goal was to determine whether and to what extent the binding of these MAbs to gD is diminished by preincubation of gD with human IgG.…”