Global sensing of the antigenic structure of herpes simplex virus gD using high-throughput array-based SPR imaging

Abstract

While HSV-2 typically causes genital lesions, HSV-1 is increasingly the cause of genital herpes. In addition, neonatal HSV infections are associated with a high rate of mortality and HSV-2 may increase the risk for HIV or Zika infections, reinforcing the need to develop an effective vaccine. In the GSK Herpevac trial, doubly sero-negative women were vaccinated with a truncated form of gD2 [gD2(284t)], then examined for anti-gD serum titers and clinical manifestations of disease. Surprisingly, few vaccinees were protected against genital HSV-2 but 86% were protected from genital HSV-1. These observations suggest that subtle differences in gD structure might influence a protective response. To better understand the antigenic structure of gD and how it impacts a protective response, we previously utilized several key anti-gD monoclonal antibodies (mAbs) to dissect epitopes in vaccinee sera. Several correlations were observed but the methodology limited the number of sera and mAbs that could be tested. Here, we used array-based surface plasmon imaging (SPRi) to simultaneously measure a larger number of protein-protein interactions. We carried out cross-competition or “epitope binning” studies with 39 anti-gD mAbs and four soluble forms of gD, including a form [gD2(285t)] that resembles the Herpevac antigen. The results from these experiments allowed us to organize the mAbs into four epitope communities. Notably, relationships within and between communities differed depending on the form of gD, and off-rate analysis suggested differences in mAb-gD avidity depending on the gD serotype and length. Together, these results show that gD1 and gD2 differ in their structural topography. Consistent with the Herpevac results, several mAbs that bind both gD1 and gD2 neutralize only HSV-1. Thus, this technology provides new insights into the antigenic structure of gD and provides a rationale as to how vaccination with a gD2 subunit may lead to protection from HSV-1 infection.

Surface Plasmon Resonance Reveals Direct Binding of Herpes Simplex Virus Glycoproteins gH/gL to gD and Locates a gH/gL Binding Site on gD

“…The green community was also divided into subcommunities (yellow and green) based on epitope mapping and competition data (11,33,38). We detected a gD-gH/gL interaction when gD was captured by any of the members of the green/yellow communities (Fig.…”

“…In our initial experiments, we used the Carterra continuous-flow microspotter (CFM)/IBIS SPR system (33)(34)(35) to print a large panel of previously characterized gD MAbs (33) onto an SPR chip ( Fig. 1A).…”

“…The gD2(285t) community map ( Fig. 1B) (33) illustrates the competitive relationships between the MAbs; those that reside in the same color community have epitopes that are located near one another. Real-time binding of gD2(285t) to a fixed MAb is illustrated in Fig.…”

“…From previous work, we knew that all members of the red community strongly compete with each other for binding to gD, and each MAb has potent neutralizing activity (11,33,36,37). This community is subdivided into red and pink subcommunities based on properties such as receptor blocking (nectin-1 only for red, both nectin-1 and HVEM for pink) (33). Here, we observed that when gD was presented via any one of the six pink subcommunity MAbs, there was a significant increase in RU upon addition of gH/gL, providing the first evidence that gD can directly bind gH/gL (Fig.…”

“…We propose that 4E3E and 4G4D partially block the gH/gL binding site on gD (Table 1). As the yellow-subcommunity MAbs bind to linear epitopes spanning residues 1 to 23 at the N terminus of gD (33,39,40), their ability to bind gH/gL binding suggests that the N terminus of gD is not involved in this interaction. At least one MAb within the green subcommunity (MC2) binds a discontinuous epitope located on the face of the gD structure adjacent to that of yellow MAb epitopes (11,41), identifying another region that is not involved with gH/gL binding.…”