Binding of TCR Multimers and a TCR-Like Antibody with Distinct Fine-Specificities Is Dependent on the Surface Density of HLA Complexes

Jianrong L Low,Gladys Yeo,Susana G Shochat,Gijsbert M Grotenbreg,Antonio Bertoletti,Adam J Gehring,David M Kranz,Anneta Naidoo,Zi Zong Ho,Yin Hoe Yau

doi:10.1371/journal.pone.0051397

Abstract

Class I Major Histocompatibility Complex (MHC) molecules evolved to sample degraded protein fragments from the interior of the cell, and to display them at the surface for immune surveillance by CD8+ T cells. The ability of these lymphocytes to identify immunogenic peptide-MHC (pMHC) products on, for example, infected hepatocytes, and to subsequently eliminate those cells, is crucial for the control of hepatitis B virus (HBV). Various protein scaffolds have been designed to recapitulate the specific recognition of presented antigens with the aim to be exploited both diagnostically (e.g. to visualize cells exposed to infectious agents or cellular transformation) and therapeutically (e.g. for the delivery of drugs to compromised cells). In line with this, we report the construction of a soluble tetrameric form of an αβ T cell receptor (TCR) specific for the HBV epitope Env183–191 restricted by HLA-A*02:01, and compare its avidity and fine-specificity with a TCR-like monoclonal antibody generated against the same HLA target. A flow cytometry-based assay with streptavidin-coated beads loaded with Env183–191/HLA-A*02:01 complexes at high surface density, enabled us to probe the specific interaction of these molecules with their cognate pMHC. We demonstrate that the TCR tetramer has similar avidity for the pMHC as the antibody, but they differ in their fine-specificity, with only the TCR tetramer being capable of binding both natural variants of the Env183–191 epitope found in HBV genotypes A/C/D (187Arg) and genotype B (187Lys). Collectively, the results highlight the promiscuity of our soluble TCR, which could be an advantageous feature when targeting cells infected with a mutation-prone virus, but that binding of the soluble oligomeric TCR relies considerably on the surface density of the presented antigen.

Highlights

Antibodies and T cell receptors (TCRs) represent two distinct classes of immune molecules that the adaptive immune system in mammals has evolved to recognize foreign pathogens
We show that the soluble TCR is both functional and highly peptide-specific using a multivalent, bead-based assay that we developed as a novel platform for probing TCR:pMHC interactions
The genes encoding the extracellular regions of the a and b chains of the Env183/A2 TCR [34], with an additional cysteine introduced in each C region [23] (Fig. 1A), were cloned into pET28a vectors and the proteins were expressed in E. coli as inclusion bodies

Summary

Introduction

Antibodies and T cell receptors (TCRs) represent two distinct classes of immune molecules that the adaptive immune system in mammals has evolved to recognize foreign pathogens. Peptide-MHC (pMHC) complexes are formed in virus-infected cells when processed viral proteins are loaded onto class I MHCs and delivered to the cell surface [3]. This enables infected cells to be recognized, typically by a CD8+ T cell, resulting, ideally, in activation of the T cell, destruction of the target cell, and clearance of the virus [4]. In hepatitis B virus (HBV) infection, which still poses a global health problem despite the availability of an effective prophylactic vaccine, CD8+ cytotoxic T lymphocytes (CTLs) play a crucial role in the antiviral response [5]. Effective control of HBV relies on robust CTL responses, and CD8+ T cell dysfunction is associated with chronic infection, which in turn carries the risk of complications such as hepatocellular carcinoma

Methods

Results

Conclusion