Figure 1.

(A) Designs of SARS-CoV-2 spike DNA and protein vaccines. In addition to the wild type S gene insert (wt), two versions of codon optimized (opt) S DNA vaccines were produced: full length S insert (FL) and truncated S insert without transmembrane and intracellular components (dTM). For the expression of recombinant S1 protein, the signal peptide of tissue plasminogen activator (tPA) replaced the nature S protein signal peptide (SP). (B) Western blot analysis to examine the expression of S DNA vaccines and recombinant S1 protein vaccine. 293 T cells were transiently transfected with either S-FL-opt or S-dTM-opt DNA plasmids and either the culture supernatant (Sup) or cell lysate (lysate) was harvested 72 h later. Recombinant S1 protein was produced from Expi293 cells and purified by HisTrap HP. S1 specific rabbit polyclonal serum L295-IV was used as the detecting antibody.