Efficacy of Opsonic and Nonopsonic Serotype 3 Pneumococcal Capsular Polysaccharide-Specific Monoclonal Antibodies against Intranasal Challenge withStreptococcus pneumoniaein Mice

Abstract

Serotype-specific antibodies to pneumococcal capsular polysaccharide (PPS) are a critical component of vaccine-mediated immunity to Streptococcus pneumoniae. In this study, we investigated the in vitro opsonophagocytic activities of three PPS-specific mouse immunoglobulin G1 monoclonal antibodies (MAbs), 1E2, 5F6, and 7A9, and determined their in vivo efficacies against intranasal challenge with WU2, a serotype 3 pneumococcal strain, in normal and immunodeficient mice. The MAbs had different in vitro activities in a pneumococcal killing assay: 7A9 enhanced killing by mouse neutrophils and J774 cells in the presence of a complement source, whereas 5F6 promoted killing in the absence, but not the presence, of complement, and 1E2 did not promote killing under any conditions. Nonetheless, all three MAbs protected normal and complement component 3-deficient mice from a lethal intranasal challenge with WU2 in passive-immunization experiments in which 10 g of the MAbs were administered intraperitoneally before intranasal challenge. In contrast, only 1E2 protected Fc␥ receptor IIB knockout (Fc␥RIIB KO) mice and mice that were depleted of neutrophils with the MAb RB6, whereas 7A9 and 5F6 required neutrophils and Fc␥RIIB to mediate protection. Conversely, 7A9 and 5F6 protected Fc␥R KO mice, but 1E2 did not. Hence, the efficacy of 1E2 required an activating Fc␥R(s), whereas 5F6 and 7A9 required the inhibitory Fc␥R (Fc␥RIIB). Taken together, our data demonstrate that both MAbs that do and do not promote pneumococcal killing in vitro can mediate protection in vivo, although their efficacies depend on different host receptors and/or components.

A Serotype 3 Pneumococcal Capsular Polysaccharide-Specific Monoclonal Antibody Requires Fcγ Receptor III and Macrophages To Mediate Protection against Pneumococcal Pneumonia in Mice

“…Murine Fc␥RI binds IgG2a; Fc␥RIIB binds IgG1, IgG2a, and IgG2b; Fc␥RIII binds IgG1, IgG2a, and IgG2b; and Fc␥RIV binds IgG2a and IgG2b (33). In a previous study, Tian et al reported that PPS3-specific mouse IgG1 MAbs that do (7A9 and 5F6) and do not (1E2) promote phagocyte-mediated opsonophagocytic killing of ST3 in vitro were each able to protect wild-type C57BL/6 (Wt) mice against lethal intranasal infection with ST3 (49). The MAbs that promoted in vitro killing (7A9 and 5F6) required Fc␥RIIB and neutrophils to mediate protection, whereas the one that did not (1E2) required the FcR common gamma chain (Fc␥R) but not Fc␥RIIB or neutrophils (49).…”

“…However, ST-specific antibodies that mediate protection against pneumococcus in mouse models, but do not promote opsonophagocytic killing in vitro (9,10,18,49), have been identified. Such antibodies include PPS3-specific human and mouse monoclonal antibodies (MAbs) that protect mice against lethal pneumonia and sepsis with ST3 (49). Understanding the mechanism(s) by which antibodies to PPS3 mediate protection is important.…”

Characterization of Gene Use and Efficacy of Mouse Monoclonal Antibodies toStreptococcus pneumoniaeSerotype 8

“…Given the discrete gene use of the PPS-and PC-specific MAbs reported herein and the observation that only PPS-specific MAbs were protective, analysis of the gene use of PPS-binding B cells could have the potential to reveal PPS specificity and possibly to predict function. Although certain PPS determinants might elicit antibodies that are less protective than others, the molecular signatures of such antibodies could also be discrete, as described for PPS3-binding MAbs (14,52). Hence, antibody structure-function relationships could hold promise as biomarkers and/or as a component of a new generation of surrogates for pneumococcal vaccine efficacy.…”

“…For infection, mice were given 50, 100, or 1,000 CFU of ST8 (6308) or 100 or 200 CFU of ST3 (WU2). This infection model is based on the historical serum potency assay (8) and has been used previously to study the efficacy of MAbs to PPS in vivo (14,43,52,55).…”

“…MAb nucleic acid sequences were determined as described previously (14,52). Briefly, mRNA was isolated from approximately 10 6 hybridoma cells and reverse transcribed to cDNA by Moloney murine leukemia virus (MMLV) reverse transcriptase (Invitrogen, Carlsbad, CA).…”