title: Calreticulin as a hydrophilic chimeric molecular adjuvant enhances IgG responses to the spike protein of severe acute respiratory syndrome coronavirus.
abstract: Fragment 450-650 of the spike (S) protein (S450-650) of severe acute respiratory syndrome-associated coronavirus (SARS-CoV) contains epitopes capable of being recognized by convalescent sera of SARS patients. Vaccination of mice with recombinant S450-650 (rS450-650) can induce Abs against SARS-CoV, although the titer is relatively low. In the present study, a fusion protein linking a fragment (residues 39-272) of murine calreticulin (CRT) to S450-650 in a prokaryotic expression system was created. Compared with target antigen alone, the recombinant fusion product (rS450-650-CRT) has much improved hydrophilicity and immunogenicity. The S450-650-specific IgG Abs of BALB/c mice subcutaneously immunized with rS450-650-CRT were in substantially higher titer (approximately fivefold more). Furthermore, the fusion protein, but not rS450-650 alone, was able to elicit S450-650-specific IgG responses in T cell deficient nude mice. Given that rCRT/39-272 can drive the maturation of bone-marrow-derived dendritic cells, directly activate macrophages and B cells, and also elicit helper T cell responses in vivo, we propose that fragment 39-272 of CRT is an effective molecular adjuvant capable of enhancing target Ag-specific humoral responses in both a T cell-dependent and independent manner. Fusion protein rS450-650-CRT is a potential candidate vaccine against SARS-CoV infection.
authors.affiliation: Department of Immunology, Peking University Health Science Center, Beijing, China.
authors.forename: Xiang
authors.initials: X
authors.lastname: Qiu
authors.forename: Chao
authors.initials: C
authors.lastname: Hong
authors.forename: Yue
authors.initials: Y
authors.lastname: Li
authors.forename: Wanrong
authors.initials: W
authors.lastname: Bao
authors.forename: Xiao-Ming
authors.initials: XM
authors.lastname: Gao
mesh_terms: D000276:Adjuvants, Immunologic / Q000008:administration & dosage* / Q000235:genetics; D000818:Animals; D000914:Antibodies, Viral / Q000097:blood*; D037282:Calreticulin / Q000008:administration & dosage* / Q000235:genetics; D005260:Female; D007074:Immunoglobulin G / Q000097:blood*; D007279:Injections, Subcutaneous; D008562:Membrane Glycoproteins / Q000276:immunology*; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000276:immunology; D045473:Severe acute respiratory syndrome-related coronavirus / Q000276:immunology*; D064370:Spike Glycoprotein, Coronavirus; D014614:Vaccines, Synthetic / Q000008:administration & dosage / Q000276:immunology; D014759:Viral Envelope Proteins / Q000276:immunology*; D014765:Viral Vaccines / Q000008:administration & dosage / Q000276:immunology*
chemical_list: D000276:Adjuvants, Immunologic; D000914:Antibodies, Viral; D037282:Calreticulin; D007074:Immunoglobulin G; D008562:Membrane Glycoproteins; D011993:Recombinant Fusion Proteins; D064370:Spike Glycoprotein, Coronavirus; D014614:Vaccines, Synthetic; D014759:Viral Envelope Proteins; D014765:Viral Vaccines; C578557:spike glycoprotein, SARS-CoV; C578553:spike protein, mouse hepatitis virus