# Monoclonal neutralizing antibodies elicited by infection with Kaposi sarcoma-associated herpesvirus reveal critical sites of vulnerability on gH/gL

## TL;DR

Scientists isolated antibodies that neutralize Kaposi sarcoma-associated herpesvirus, identifying key protein regions that could help in vaccine development.

## Contribution

The study identifies five epitope clusters on the gH/gL protein and two potent neutralizing antibodies targeting the EphA2 binding site.

## Key findings

- Twelve monoclonal antibodies bind to five distinct epitope clusters on the gH/gL complex.
- Seven antibodies neutralize Kaposi sarcoma-associated herpesvirus infection in epithelial cells.
- Two potent antibodies block the EphA2 receptor-ligand interaction, revealed through structural analyses.

## Abstract

Kaposi sarcoma-associated herpesvirus (KSHV) is an oncogenic virus that causes Kaposi sarcoma, primary effusion lymphoma and multicentric Castleman disease. A vaccine that prevents KSHV infection or serves in the treatment of KSHV-related diseases represents a critical unmet need, however, the types of immune responses a vaccine should elicit have not been well defined. The gH/gL glycoprotein complex is an important target of KSHV-neutralizing antibodies, but the epitope specificities targeted by these antibodies remain unknown. Here, we isolated 12 gH/gL-specific monoclonal antibodies (mAbs) from KSHV-infected donors and performed structure/function analyses. These mAbs bind recombinant gH/gL with nanomolar affinities and epitope binning analyses revealed that the mAbs bind to 5 epitope clusters on gH/gL. Seven mAbs were able to neutralize KSHV infection of epithelial cell lines. Two potent neutralizing mAbs mapped to the EphA2 binding site as determined by inhibition of the receptor-ligand interaction and negative stain electron microscopy (nsEM) of the mAb/gH/gL complex. The epitopes of other neutralizing mAbs targeting novel sites of vulnerability were determined by a combination of cryogenic electron microscopy and nsEM. Together, these mAbs help to define the relevant epitope targets for KSHV vaccine design, have utility in understanding the role of antibodies in preventing KSHV infection, enable the development of immunotherapy approaches, and provide valuable tools to understand the molecular details of the KSHV entry process.

KSHV is an oncogenic virus that can cause cancer in infected individuals. The virus is most prevalent in sub-Saharan Africa and in men who have sex with men. It is possible this virus could be prevented with an effective vaccine, however, the immune response to this virus has not been well defined. gH/gL, a protein essential for viral fusion, plays an important role in infection and could be a possible vaccine target. To better understand the antibody response to this protein, we sought to isolate and characterize monoclonal antibodies that can bind gH/gL and neutralize viral infection. In this study, we isolate and characterize twelve monoclonal antibodies that could bind to five different regions of the gH/gL protein. Seven of these antibodies can neutralize infection, with two being able to block the gH/gL EphA2 receptor-ligand interaction.