Codelivery of improved immune complex and virus-like particle vaccines containing Zika virus envelope domain III synergistically enhances immunogenicity

Abstract

a b s t r a c tZika virus (ZIKV) reemergence poses a significant health threat especially due to its risks to fetal development, necessitating safe and effective vaccines that can protect pregnant women. Zika envelope domain III (ZE3) has been identified as a safe and effective vaccine candidate, however it is poorly immunogenic. We previously showed that plant-made recombinant immune complex (RIC) vaccines are a robust platform to improve the immunogenicity of weak antigens. In this study, we altered the antigen fusion site on the RIC platform to accommodate N-terminal fusion to the IgG heavy chain (N-RIC), and thus a wider range of antigens, with a resulting 40% improvement in RIC expression over the normal C-terminal fusion (C-RIC). Both types of RICs containing ZE3 were efficiently assembled in plants and purified to >95% homogeneity with a simple one-step purification. Both ZE3 RICs strongly bound complement receptor C1q and elicited strong ZE3-specific antibody titers that correlated with ZIKV neutralization. When either N-RIC or C-RIC was codelivered with plant-produced hepatitis B core (HBc) virus-like particles (VLP) displaying ZE3, the combination elicited 5-fold greater antibody titers (>1,000,000) and more strongly neutralized ZIKV than either RICs or VLPs alone, after only two doses without adjuvant. These findings demonstrate that antigens that require a free N-terminus for optimal antigen display can now be used with the RIC system, and that plant-made RICs and VLPs are highly effective vaccines targeting ZE3. Thus, the RIC platform can be more generally applied to a wider variety of antigens.

A highly expressing, soluble, and stable plant-made IgG fusion vaccine strategy enhances antigen immunogenicity in mice without adjuvant

“…The construction of a geminiviral replicon plant expression vector for ZE3, as well as its fusion to the 6D8 C-terminus (pBYR11eM-h6D8ZE3, referred to here as construct “HLZe”) or N-terminus with epitope tag (pBYR11eMa-BAZE3-Hgp371) or without epitope tag (pBYR11eMa-BAZE3-H) have been previously described (Diamos et al, 2020b, 2020a) A vector pBYKEMd2-6D8 expressing the full 6D8 mAb without ZE3 fusion (construct “HL”) has been previously described (Diamos et al, 2020b, 2020a). To create a vector expressing only the light chain of 6D8, pBYKEMd2-6D8 was digested with XhoI and the vector was self-ligated to yield pBYKEMd-6D8K.…”

Combating Human Viral Diseases: Will Plant-Based Vaccines Be the Answer?

“…More than 69 countries have reported Zika virus infections [ 214 ] between 2015 and 2017. In 2016, the World Health Organization declared the Zika virus infections as a Public Health Emergency of International Concern.…”

A Highly Expressing, Soluble, and Stable Plant-Made IgG Fusion Vaccine Strategy Enhances Antigen Immunogenicity in Mice Without Adjuvant

“…The construction of a geminiviral replicon plant expression vector for ZE3, as well as its fusion to the 6D8 C-terminus (pBYR11eM-h6D8ZE3, referred to here as construct "HLZe") or N-terminus with epitope tag (pBYR11eMa-BAZE3-Hgp371) or without epitope tag (pBYR11eMa-BAZE3-H) have been previously described (27,31) A vector pBYKEMd2-6D8 expressing the full 6D8 mAb without ZE3 fusion (construct "HL") has been previously described (27,31). To create a vector expressing only the light chain of 6D8, pBYKEMd2-6D8 was digested with XhoI and the vector was self-ligated to yield pBYKEMd-6D8K.…”

“…The resulting molecules self-interact and form highly immunogenic antigen-antibody clusters. Past research has shown the potential for RIC-like molecules to produce promising vaccine candidates for Clostridium tetani (21), Ebola virus (22,23), Mycobacterium tuberculosis (24), dengue virus (25), human papillomavirus (26) and Zika virus (27).…”

“…However, like many subunit vaccines consisting of viral antigens, it is not strongly immunogenic on its own, necessitating high doses with adjuvant and repeated immunizations (30). We have previously shown that RIC carrying ZE3 elicits strong immune responses (27). However, traditional RIC may be undesirable, as the large complex size renders them poorly soluble and limits their viability as a vaccine candidate (26).…”