Human papillomavirus (HPV) type 16 E7 protein bodies cause tumour regression in mice

Abstract

BackgroundHuman papillomaviruses (HPV) are the causative agents of cervical cancer in women, which results in over 250 000 deaths per year. Presently there are two prophylactic vaccines on the market, protecting against the two most common high-risk HPV types 16 and 18. These vaccines remain very expensive and are not generally affordable in developing countries where they are needed most. Additionally, there remains a need to treat women that are already infected with HPV, and who have high-grade lesions or cervical cancer.MethodsIn this paper, we characterize the immunogenicity of a therapeutic vaccine that targets the E7 protein of the most prevalent high-risk HPV - type 16 – the gene which has previously been shown to be effective in DNA vaccine trials in mice. The synthetic shuffled HPV-16 E7 (16E7SH) has lost its transforming properties but retains all naturally-occurring CTL epitopes. This was genetically fused to Zera®, a self-assembly domain of the maize γ-zein able to induce the accumulation of recombinant proteins into protein bodies (PBs), within the endoplasmic reticulum in a number of expression systems.ResultsHigh-level expression of the HPV 16E7SH protein fused to Zera® in plants was achieved, and the protein bodies could be easily and cost-effectively purified. Immune responses comparable to the 16E7SH DNA vaccine were demonstrated in the murine model, with the protein vaccine successfully inducing a specific humoral as well as cell mediated immune response, and mediating tumour regression.ConclusionsThe fusion of 16E7SH to the Zera® peptide was found to enhance the immune responses, presumably by means of a more efficient antigen presentation via the protein bodies. Interestingly, simply mixing the free PBs and 16E7SH also enhanced immune responses, indicating an adjuvant activity for the Zera® PBs.

The increasing value of plant-made proteins

“…Fusion proteins may also function as integrated adjuvants to increase vaccine efficacy at lower costs, e.g. the CTB and zein domains can both act as adjuvants [8,40]. …”

Plant-based vaccines against viruses

“…Our group has recently explored the potential of a novel HPV-16 E7-derived gene construct -a synthetic shuffled HPV-16 E7 (16E7SH) that has lost its transforming properties, but retains all naturally-occurring CTL epitopes -for expression in plants as a candidate therapeutic vaccine [102]. The E7SH gene has previously successfully been used as a DNA vaccine in a mouse tumour model, eliciting potent cellular and humoral immune responses, including tumour protection and regression [103].…”

Plant‐derived protein bodies as delivery vehicles for recombinant proteins into mammalian cells

“…Furthermore, it was discovered that the N‐terminal 93 amino acids of 27 kDa γ‐zein (abbreviated gz93 from here on) are sufficient to produce PBs in other plants, and even in heterologous expression systems such as fungal, insect, and mammalian cells (Llop‐Tous et al, 2010; Torrent et al, 2009). Various proteins with different properties in terms of molecular mass and function, including growth factors (Torrent et al, 2009), viral vaccine candidate proteins (Hofbauer et al, 2016; Mbewana, Mortimer, Pêra, Hitzeroth, & Rybicki, 2015; Whitehead et al, 2014), and enzymes (Llop‐Tous, Ortiz, Torrent, & Ludevid, 2011), have been successfully incorporated into newly induced PBs in plants like Nicotiana benthamiana when fused to gz93. N. benthamiana is frequently used for the production of biopharmaceuticals because it is well suited for the transient expression of recombinant proteins, and this method offers advantages over other expression systems in terms of speed, safety, scalability, and reduced upstream production costs.…”