Recognition of core-derived epitopes from a novel HBV-targeted immunotherapeutic by T-cells from patients infected by different viral genotypes

Abstract

Hepatitis B virus (HBV) infects millions of people worldwide and is a leading cause of liver cirrhosis and hepatocellular carcinoma. Current therapies based on nucleos(t)ide analogs or pegylated-interferon-α lead to control of viral replication in most patients but rarely achieve cure. A potential strategy to control chronic hepatitis B is to restore or induce functional anti-HBV T-cell immune responses using HBV-specific immunotherapeutics. However, viral diversity is a challenge to the development of this class of products as HBV genotypes display a sequence diversity of up to 8%. We have developed a novel HBV-targeted immunotherapeutic, TG1050, based on a non-replicative Adenovirus vector encoding a unique and large fusion protein composed of multiple antigenic regions derived from a HBV genotype D sequence. Using peripheral blood mononuclear cells from 23 patients chronically infected by five distinct genotypes (gt A, B, C, D and E) and various sets of peptides encompassing conserved versus divergent regions of HBV core we have measured ability of TG1050 genotype D core-derived peptides to be recognized by T-cells from patients infected by various genotypes. Overall, PBMCs from 78% of genotype B or C- and 100% genotype A or E-infected patients lead to detection of HBV core-specific T-cells recognizing genotype D antigenic domains located both in conserved and variable regions. This proof-of-concept study supports the clinical development of TG1050 in large patient populations independently of infecting genotypes.

Introduction

Infection by hepatitis B virus (HBV) is one of the major public health challenges worldwide. While the availability of a preventive vaccine has reduced the number of new HBV infections, it does not benefit the 370 millions of chronic hepatitis B (CHB) patients already infected by the virus. Approximately one third of these chronically infected individuals will die from serious liver disease, such as cirrhosis, hepatocellular carcinoma and liver failure [1]. Current CHB therapies include nucleos(t)ide analogs and pegylated-IFNα but despite their ability to control HBV replication in the great majority of patients and to improve liver histology, complete HBV cure is achieved in only 3–5% of patients [1].

Immune correlates of control of viral replication have been described in cohort studies of patients resolving infection and involve mainly the development of broad, robust and poly-functional CD8+ and CD4+ T-cell responses targeting multiple HBV antigens among which the critical core antigen [2], [3], [4]. In CHB patients, the breath and the magnitude of these immune responses are reduced and the antigen specificity is narrowed [5]. Because of such strong interplay between T-cell immunity and control of viral replication, efforts at developing HBV-specific immune-based interventions are gaining attention. These have for objective to induce and/or recall immune responses similar to those found in HBV resolvers. The development of this novel class of agents, also referred to as immunotherapeutics or therapeutic vaccines [6] meets with a number of challenges: choice of broad and most appropriate antigens, capacity of the vaccine vector to induce sustained T-cell based immunity in face of virus-specific T-cell exhaustion typically found in the CHB carriers, generation of cytolytic-based mechanisms to eliminate infected cells and associated covalently closed circular DNA without exacerbating liver inflammation, finally accounting for the genetic diversity of HBV viruses (10 different genotypes) [7]. TG1050 is a novel immunotherapeutic product based on a non-replicative Adenovirus 5 vector encoding a unique and large fusion protein composed of modified HBV core and polymerase and selected domains of the Env proteins. TG1050, based on a genotype (gt) D HBV sequence was evaluated in a variety of HBV-naïve mouse lines as well as in HBV-persistent mouse models including the model described by Dion et al. [8], in which TG1050 was shown to display antiviral activities [9]. The core antigen is highly immunogenic and described to contain epitopes associated with resolution of infection [10], it thus represents a key antigen in TG1050. Hence, it is important to assess whether TG1050-encoded core has the capacity to induce broadly reactive T-cells recognizing epitopes present in CHB patients infected by non-genotype D isolates in order to support a broad application of TG1050 in the clinic. We report here a human cohort study designed to analyze the capacity of TG1050 encoded core peptide epitopes to stimulate and recall functional T-cell responses in CHB patients infected by genotype A, B, C, D and E.