Nucleic acid vaccine candidates encapsulated with mesoporous silica nanoparticles against MERS-CoV

Abstract

Middle East respiratory coronavirus (MERS-CoV) is a newly emergent, highly pathogenic coronavirus that is associated with 34% mortality rate. MERS-CoV remains listed as priority pathogen by the WHO. Since its discovery in 2012 and despite the efforts to develop coronaviruses vaccines to fight against SARS-CoV-2, there are currently no MERS-CoV vaccine that has been approved. Therefore, there is high demand to continue on the development of prophylactic vaccines against MERS-CoV. Current advancements in vaccine developments can be adapted for the development of improved MERS-CoV vaccines candidates. Nucleic acid-based vaccines, including pDNA and mRNA, are relatively new class of vaccine platforms. In this work, we developed pDNA and mRNA vaccine candidates expressing S.FL gene of MERS-CoV. Further, we synthesized a silane functionalized hierarchical aluminosilicate to encapsulate each vaccine candidates. We tested the nucleic acid vaccine candidates in mice and evaluated humoral antibodies response. Interestingly, we determined that the non-encapsulated, codon optimized S.FL pDNA vaccine candidate elicited the highest level of antibody responses against S.FL and S1 of MERS-CoV. Encapsulation of mRNA with nanoporous aluminosilicate increased the humoral antibody responses, whereas encapsulation of pDNA did not. These findings suggests that MERS-CoV S.FL pDNA vaccine candidate induced the highest level of humoral responses. This study will enhance further optimization of nanosilica as potential carrier for mRNA vaccines. In conclusion, this study suggests MERS-CoV pDNA vaccine candidate as a suitable vaccine platform for further pivotal preclinical testings.

Keywords: APTMOS; DPP-4; HAS; IM; MERS-CoV; RBD; SC; coronavirus; mRNA; pDNA; silica; spike; vaccine.

Figure 1.

Codon quality of MERS-CoV S gene by obtained GeneOptimizer. (a,b) Histograms showing the percentage of sequence codons that fall within selected optimization parameters. The quality value of the most frequently used codons for given amino acids in the homo sapiens is set to 100. The plots show the quality of codons at the indicated codon position. (c) Average GC contents in 40 bp window centered at the indicated nucleotide position with an average GC content equal to 56%.

Figure 2.

Agarose gel electrophoresis for the synthesized of pDNA and mRNA vaccines encoding S gene of MERS-CoV. (a). Two clones of pDNA expressing S gene. Correct band size of S gene 4000 bp and pVAX1 (3000) is showing in the gel double cut (DC) restriction analysis of BamHI and NheI. (b). In-vitro (IVT) synthesized RNA of. The correct band size of 4000 bp is showing in parallel with RNA marker.

Figure 3.

X-ray diffraction of (a) HAS and (b) APTMOS-HAS, (c and d) Thermogravimetric analysis of APTMOS-HAS, nitrogen adsorption isotherm of (E) ZSM-5, (f) HAS, and (g) APTMOS-HAS and pore size distribution of (h) ZSM-5, (i) HAS, and (j) APTMOS-HAS.

Figure 4.

(a–d) Transmission electron microscope images depicting morphology of (a) HAS and (b–d) APTMOS-HAS.

Figure 5.

0.8% agarose gel analysis for the MERS-CoV vaccine candidates. Samples in the left lane were subjected to heat inactivation at 95°C for 1 hour and samples are shown as follow: pDNA (Untreated), pDNA (Heat Inactivated), pDNA+HAS (Heat Inactivated). Samples in the right lane were subjected to TURBO DNase digestion and samples are shown as follow: pDNA (Untreated), pDNA (Turbo DNase), pDNA+HAS (TURBO DNase).

Figure 6.

Humoral immune response in vaccinated mice groups against MERS-CoV S.FL. Binding antibody responses was measured by indirect ELISA measured at week 0 (a), week 2 (b), week 4 (c), week 6 (d). Statistical analysis was performed using one way ANOVA.

Figure 7.

Binding antibodies responses in vaccinated groups elicited against MERS-CoV S1 and S.FL. Binding antibody responses was measured by indirect ELISA measured at week 6. Statistical analysis was performed using two-way ANOVA.