Definition: In this task, you're given a paragraph from the research paper and your task is to generate a suitable title for the research paper based on the given paper. Under 100 words is a good title length.
Input: Efforts towards developing a vaccine for Middle East respiratory syndrome coronavirus (MERS-CoV) have yielded promising results. Utilizing a variety of platforms, several vaccine approaches have shown efficacy in animal models and begun to enter clinical trials. In this review, we summarize the current progress towards a MERS-CoV vaccine and highlight potential roadblocks identified from previous attempts to generate coronavirus vaccines. Viruses 2019, 11, 74 2 of 17 Preclinical vaccine development for both SARS-CoV and MERS-CoV has largely aimed to stimulate a robust immune response against the viral envelope-protruding spike (S) glycoprotein [28, 29] , a class I fusion protein, and/or the nucleocapsid (N) protein [30, 31] . MERS-CoV S is proteolytically cleaved by host furin [32] during maturation into an S1 domain responsible for binding to DPP4 as well as an S2 domain containing two heptad-repeat regions that facilitate membrane fusion (Figure 1 ). The S1 domain can be further divided into the N-terminal domain (NTD), or S1 A , associated with binding sialic acid [33] , and the receptor binding domain (RBD), comprising the majority of the C-terminal domain of S1. Cryo-electron microscopy studies have shown that the RBD is flexible and opens upward or away from the viral envelope in order to establish contact with DPP4, which may expose S2' [34], a second protease cleavage site within S2. Cleavage at S2' is necessary for membrane fusion upon viral entry [32] . The centrality of S to viral entry helps explain why antibodies that target it are potently neutralizing [35] . On the other hand, while CoV N proteins are abundantly expressed during infection [36] , immunization with SARS-CoV N did not induce strongly neutralizing antibodies [37], likely because N is not displayed on the viral surface. However, N is more conserved than S within CoV lineage [38] , and vaccination with SARS-CoV N was shown to induce cytotoxic T cell responses in mice [39] . Therefore, N may help induce cell-mediated immunity to CoV infection [40] , as may S [41]. CD4+ and CD8+ T cell responses from recovered MERS-CoV patients were particularly strong towards N peptides [42] . However, vaccination with N-based immunogens may carry risks associated with T h 2-related eosinophilic immune enhancement [43] , as may S-based vaccines [44] . Notwithstanding, because of the protection afforded by the robust immune response it generates, S has been the target of most vaccine candidates for MERS-CoV. In this review, we summarize the current state of MERS-CoV vaccine candidates and also describe potential barriers to MERS-CoV vaccine efficacy that first surfaced during research on developing a SARS-CoV vaccine.

viruses Middle East Respiratory Syndrome Vaccine Candidates: Cautious Optimism