Novel Immunoprotective Proteins of Streptococcus pneumoniae Identified by Opsonophagocytosis Killing Screen

Abstract

The success of polysaccharide conjugate vaccines represents a major advance in the prevention of pneumococcal disease, but the power of these vaccines is limited by partial spectrum of coverage and high cost. Vaccines using immunoprotective proteins are a promising alternative type of pneumococcal vaccines. In this study, we constructed a library of antisera against conserved pneumococcal proteins predicted to be associated with cell surface or virulence using a combination of bioinformatic prediction and immunization of rabbits with recombinant proteins. Screening of the library by an opsonophagocytosis killing (OPK) assay identified the OPK-positive antisera, which represented 15 (OPK-positive) proteins. Further tests showed that virtually all of these OPK-positive antisera conferred passive protection against lethal infection of virulent pneumococci. More importantly, immunization with recombinant forms of three OPK-positive proteins (SP148, PBP2b, and ScpB), alone or in combination, conferred significant protection against lethal challenge of pneumococcal strains representing capsular serotypes 3, 4, and 6A in a mouse sepsis model. To our best knowledge, this work represents the first example in which novel vaccine candidates are successfully identified by the OPK screening. Our data have also provided further confirmation that the OPK activity may serve as a reliable surrogate for evaluating vaccine efficacy of pneumococcal proteins.

The Modified Surface Killing Assay Distinguishes between Protective and Nonprotective Antibodies to PspA

“…Our present results provide encouragement that the modified OPKA that detects protection by antibody to PspA (51) might also be useful as an in vitro functional assay for human antibody to PspA. It should also be noted that, using a different OPKA to study antisera to 17 separate proteins, it was found that of the 17 different OPKA-positive antisera, all but 1 gave passive protection in mice (52).…”

“…It is well established that human and mouse antibodies to PspA can actively and passively protect mice from lethal pneumococcal challenge (9, 15, 52, 55, 56). One hurdle that must be overcome for PspA to move into efficacy trials has been the lack of an accepted in vitro functional assay to screen sera from immunized humans for changes in their protective potential.…”

“…OPKA fails to detect the protection elicited by other antigens probably because an OPKA design that excludes the detection of background protection was settled on. We suspect that this background protection is likely the result of antibodies to other antigens of pneumococci (25, 47, 52). There have been several demonstrations of functional in vitro assays that detect the protection mediated by antibodies to pneumococcal proteins (23, 51–53).…”

“…We suspect that this background protection is likely the result of antibodies to other antigens of pneumococci (25, 47, 52). There have been several demonstrations of functional in vitro assays that detect the protection mediated by antibodies to pneumococcal proteins (23, 51–53). One such assay, the modified surface killing assay (MSKA), detects the in vitro killing of pneumococci mediated by monoclonal antibodies (MAbs) to PspA (23).…”

SERUM ANTIBODY RESPONSES AGAINST CARBAPENEM-RESISTANTKLEBSIELLA PNEUMONIAEIN INFECTED PATIENTS

“…A key attribute commonly associated with efficacy of CPS specific Ab-mediated immunity is opsonophagocytosis (22, 23). To assess the efficacy of different PD poly-IgGs, we performed opsonophagocytosis experiments in J774 macrophages with Poly-IgG #207 , poly-IgG #219 , and poly-IgG #116 purified from patients infected with SBU219 ( wzi154 ), SBU116 ( wzi50 ), and SBU207 ( wz i 29 ).…”