title: Searching for an ideal vaccine candidate among different MERS coronavirus receptor-binding fragments--the importance of immunofocusing in subunit vaccine design.
abstract: The newly emerged Middle East respiratory syndrome coronavirus (MERS-CoV) is currently spreading among humans, making development of effective MERS vaccines a high priority. A defined receptor-binding domain (RBD) in MERS-CoV spike protein can potentially serve as a subunit vaccine candidate against MERS-CoV infections. To identify an ideal vaccine candidate, we have constructed five different versions of RBD fragments, S350-588-Fc, S358-588-Fc, S367-588-Fc, S367-606-Fc, and S377-588-Fc (their names indicate their residue range in the spike protein and their C-terminal Fc tag), and further investigated their receptor binding affinity, antigenicity, immunogenicity, and neutralizing potential. The results showed that S377-588-Fc is among the RBD fragments that demonstrated the highest DPP4-binding affinity and induced the highest-titer IgG antibodies in mice. In addition, S377-588-Fc elicited higher-titer neutralizing antibodies than all the other RBD fragments in mice, and also induced high-titer neutralizing antibodies in immunized rabbits. Structural analysis suggests that S377-588-Fc contains the stably folded RBD structure, the full receptor-binding site, and major neutralizing epitopes, such that additional structures to this fragment introduce non-neutralizing epitopes and may also alter the tertiary structure of the RBD. Taken together, our data suggest that the RBD fragment encompassing spike residues 377-588 is a critical neutralizing receptor-binding fragment and an ideal candidate for development of effective MERS vaccines, and that adding non-neutralizing structures to this RBD fragment diminishes its neutralizing potential. Therefore, in viral vaccine design, it is important to identify the most stable and neutralizing viral RBD fragment, while eliminating unnecessary and non-neutralizing structures, as a means of "immunofocusing".
authors.affiliation: Lindsley F. Kimball Research Institute, New York Blood Center, New York, NY, USA.
authors.forename: Cuiqing
authors.initials: C
authors.lastname: Ma
authors.affiliation: Lindsley F. Kimball Research Institute, New York Blood Center, New York, NY, USA.
authors.forename: Lili
authors.initials: L
authors.lastname: Wang
authors.affiliation: Department of Microbiology and Immunology and Center for Biodefense and Emerging Disease, University of Texas Medical Branch, Galveston, TX, USA.
authors.forename: Xinrong
authors.initials: X
authors.lastname: Tao
authors.affiliation: Lindsley F. Kimball Research Institute, New York Blood Center, New York, NY, USA.
authors.forename: Naru
authors.initials: N
authors.lastname: Zhang
authors.affiliation: Department of Pharmacology, University of Minnesota Medical School, Minneapolis, MN, USA.
authors.forename: Yang
authors.initials: Y
authors.lastname: Yang
authors.affiliation: Department of Microbiology and Immunology and Center for Biodefense and Emerging Disease, University of Texas Medical Branch, Galveston, TX, USA.
authors.forename: Chien-Te K
authors.initials: CK
authors.lastname: Tseng
authors.affiliation: Department of Pharmacology, University of Minnesota Medical School, Minneapolis, MN, USA.
authors.forename: Fang
authors.initials: F
authors.lastname: Li
authors.affiliation: State Key Laboratory of Pathogen and Biosecurity, Beijing Institute of Microbiology and Epidemiology, Beijing, China.
authors.forename: Yusen
authors.initials: Y
authors.lastname: Zhou
authors.affiliation: Lindsley F. Kimball Research Institute, New York Blood Center, New York, NY, USA.|Key Laboratory of Medical Molecular Virology of Ministries of Education and Health, Shanghai Medical College and Institute of Medical Microbiology, Fudan University, Shanghai, China.
authors.forename: Shibo
authors.initials: S
authors.lastname: Jiang
authors.affiliation: Lindsley F. Kimball Research Institute, New York Blood Center, New York, NY, USA.
authors.forename: Lanying
authors.initials: L
authors.lastname: Du
mesh_terms: D000818:Animals; D057134:Antibodies, Neutralizing / Q000097:blood; D000914:Antibodies, Viral / Q000097:blood; D000956:Antigens, Viral / Q000276:immunology; D018352:Coronavirus Infections / Q000517:prevention & control; D005260:Female; D006801:Humans; D007141:Immunoglobulin Fc Fragments / Q000276:immunology; D007074:Immunoglobulin G / Q000097:blood; D008807:Mice, Inbred BALB C; D065207:Middle East Respiratory Syndrome Coronavirus; D009500:Neutralization Tests; D011817:Rabbits; D000085064:Receptors, Coronavirus; D011991:Receptors, Virus / Q000378:metabolism*; D064370:Spike Glycoprotein, Coronavirus / Q000276:immunology*; D022223:Vaccines, Subunit / Q000276:immunology; D014765:Viral Vaccines / Q000276:immunology*
chemical_list: D057134:Antibodies, Neutralizing; D000914:Antibodies, Viral; D000956:Antigens, Viral; D007141:Immunoglobulin Fc Fragments; D007074:Immunoglobulin G; D000085064:Receptors, Coronavirus; D011991:Receptors, Virus; D064370:Spike Glycoprotein, Coronavirus; D022223:Vaccines, Subunit; D014765:Viral Vaccines
keywords: Critical neutralizing domain; Immunofocusing; MERS; MERS-CoV; Receptor-binding domain; Spike protein