title: Correlation between in vitro complement deposition and passive mouse protection of anti-pneumococcal surface protein A monoclonal antibodies.
abstract: The shortcomings of the licensed polysaccharide-based pneumococcal vaccine are driving efforts toward development of a protein-based vaccine that is serotype independent and effective in all age groups. An opsonophagocytic killing assay (OPKA) is used to evaluate the antibody response against polysaccharide-based pneumococcal vaccines. However, the OPKA is not reliable for noncapsular antigens. Thus, there is a need to develop an in vitro surrogate for protection for protein vaccine candidates like pneumococcal surface antigen A (PspA). PspA is a serologically variable cell surface virulence factor. Based on its sequence, PspA has been classified into families 1 (clade 1 and 2), 2 (clades 3, 4 and 5), and 3 (clade 6). Here, we report the characterization of 18 IgG anti-PspA monoclonal antibodies (anti-PspA(hkR36A) MAbs) generated from mice immunized with heat-killed strain R36A (clade 2). An enzyme-linked immunosorbent assay (ELISA)-based analysis of the reactivity of the MAbs with recombinant PspAs from the 6 clades indicated that they were family 1 specific. This was confirmed by flow cytometry using a hyperimmune serum generated against PspA from R36A. Eight MAbs that bind at least one clade 1- and clade 2-expressing strain were evaluated for complement deposition, bactericidal activity, and passive protection. The anti-PspA(hkR36A) MAb-dependent deposition of complement on pneumococci showed a positive correlation with passive protection against strain WU2 (r = 0.8783, P = 0.0041). All of our protective MAbs showed bactericidal activity; however, not all MAbs that exhibited bactericidal activity conferred protection in vivo. The protective MAbs described here can be used to identify conserved protection eliciting B cell epitopes for engineering a superior PspA-based vaccine.
authors.affiliation: Molecular Immunology Laboratory, National Institute of Immunology, New Delhi, India Department of Biotechnology, University of Kashmir, Srinagar, India.
authors.forename: Naeem
authors.initials: N
authors.lastname: Khan
authors.affiliation: Department of Biotechnology, University of Kashmir, Srinagar, India.
authors.forename: Raies Ahmad
authors.initials: RA
authors.lastname: Qadri
authors.affiliation: Molecular Immunology Laboratory, National Institute of Immunology, New Delhi, India devinder@nii.ac.in.
authors.forename: Devinder
authors.initials: D
authors.lastname: Sehgal
mesh_terms: D000818:Animals; D000907:Antibodies, Bacterial / Q000008:administration & dosage / Q000276:immunology*; D000911:Antibodies, Monoclonal / Q000008:administration & dosage / Q000276:immunology*; D001426:Bacterial Proteins / Q000276:immunology*; D003165:Complement System Proteins / Q000276:immunology* / Q000378:metabolism; D005260:Female; D007116:Immunization, Passive / Q000379:methods*; D008297:Male; D008807:Mice, Inbred BALB C; D008808:Mice, Inbred CBA; D011008:Pneumococcal Infections / Q000517:prevention & control*; D016896:Treatment Outcome
chemical_list: D000907:Antibodies, Bacterial; D000911:Antibodies, Monoclonal; D001426:Bacterial Proteins; C051592:pneumococcal surface protein A; D003165:Complement System Proteins