6E and F). Our results show that an adenoviral-based vaccine that expresses full-length or the S1 subunits of the S protein can induce MERS-CoV-specific neutralizing antibody responses in mice. It will be important to demonstrate whether

dromedary camels vaccinated with Rapamycin purchase these candidate vaccines or convalescing from MERS-CoV infection have similar responses and will be protected from MERS-CoV challenge, since this may indicate whether such vaccine-induced responses are indeed protective and future use of the Ad5.MERS-S vaccine as a veterinary vaccine in dromedary camels would be possible. Previous studies have shown that RBDs of SARS-CoV presenting in the S1 subunit strongly react with antisera from SARS patients in the convalescent phase, and depletion of RBD-specific antibodies from SARS patients results in significant elimination of the neutralizing activity [43]. The RBD is the main domain that induces neutralizing antibody and CB-839 clinical trial T-cell immune responses against SARS-CoV infection [44]. A truncated RBD of MERS-CoV S protein was recently reported to potently inhibit viral infection and induce strong neutralizing antibody responses [45] and [46]. SARS-CoV S and S2, but neither S1 nor other structural proteins, can induce apoptosis in Vero E6 cells [47] and [48] and no histopathological

changes were observed in various tissues of rats immunized with a recombinant adenovirus containing a truncated S1 fragment of the SARS-CoV [49]. In contrast, vaccination with recombinant modified MVA expressing SARS-CoV S protein is associated with enhanced hepatitis after challenge with SARS-CoV [50] and [51] and SARS-CoV has been shown to infect hepatocytes and cause hepatitis in some human cases [51], [52] and [53], raising concerns about the safety of a vaccine that contains the full-length SARS-CoV S protein. A causal relationship between the induction of hepatitis and the full-length nature of the S protein could not be conclusively demonstrated; it can be presumed that the S1 gene has less risk for spontaneous recombination with wild type virus following the generation of new virus types. Thus, we believe that an S1-expressing MERS-CoV vaccine would

be a preferable vaccine candidate format. However, an alternative S antigen format such as the entire S-ectodomain or CYTH4 the S RBD domain could be evaluated for comparison. Since the capacity of our immunization strategy to protect from infection will require challenge tests in clinically relevant MERS-CoV disease animal models such as dromedary camels, establishment of such a model will also be important to exclude the potential for vaccine-induced immunopathology, as seen in the feline infectious peritonitis virus model [54] and [55]. To this end, a mouse model for MERS-CoV infection that was generated by prior transduction of the animals with an adenoviral vector expressing the human host-cell receptor dipeptidyl peptidase 4 (hDPP4) was recently reported [56].