VelcroVax: a “Bolt-On” Vaccine Platform for Glycoprotein Display

Abstract

The hepatitis B core protein (HBc) forms noninfectious virus-like particles, which can be modified to present a capturing molecule, allowing suitably tagged antigens to be bound on their surface. This system can be adapted and provides the foundation for a universal “bolt-on” vaccine platform (termed VelcroVax) that can be easily and rapidly modified to generate nanoparticle vaccine candidates.

A VLP vaccine platform comprising the core protein of hepatitis B virus with N-terminal antigen capture

“…Gradient fractions were then analysed by Western blot which confirmed the presence of N-VelcroVax in the middle fractions of the gradient, the expected position for Hbc VLPs (Fig. 2A) [16]. Examination of the peak fraction (fraction 5) by negative stain transmission electron microscopy (TEM) showed VLPs of the expected morphology (Fig.…”

“…We previously generated a tandem HBc system, in which two copies of HBc protein are genetically linked and an anti-SUMO Affimer is inserted into the MIR of one of the HBc monomers (termed VelcroVax). This was able to bind SUMO-tagged target antigens for presentation as a multimeric VLP vaccine candidate [16]. Here, we have modified a monomeric HBc protein containing a 5 amino acid insertion into the MIR, termed wt HBc 190 (Fig.1A), by introducing the anti-SUMO Affimer sequence (Fig.…”

“…Moreover, VLPs are able to elicit both humoral and cellular immune responses initiating the production of specific antibodies and activating cytotoxic T-cells [10–13]. In addition to acting as antigens themselves, VLPs can be modified to display foreign epitopes [14–16]. A key advantage of using VLP-based vaccine platforms is the ability to present antigens in a dense, highly repetitive manner, which leads to cross-linking of B cell receptors (BCRs) and B cell activation.…”

“…The dimeric assembly results in the formation of 4 helix bundles (spikes) which project from the particle surface and a sequence at the tips of the spikes comprises the major immunodominant region (MIR). The MIR has been used as a preferred site for insertion of foreign epitopes because of its immunodominance [16, 23, 24] but this also poses challenges. There is a potential for steric clashes when two closely located copies of the inserted sequence are present at the tips of the spikes [23, 25].…”

“…We previously addressed this problem by fusing two copies of HBc protein to produce tandem HBc VLPs, which allows the insertion of a foreign sequence into one MIR, leaving the other MIR in the tandem partner unmodified, resulting in the presence of only one foreign epitope per spike [23]. This approach allowed us to develop VelcroVax, incorporating an antigen capture sequence, an Affimer (a non-antibody high affinity artificial binding protein), inserted at a single MIR per spike [16]. Although these constructs form VLPs when expressed in eukaryotic systems, such as yeast or plants, they do not assemble efficiently when expressed in E.coli .…”