Structure-Function Relationships for Human Antibodies to Pneumococcal Capsular Polysaccharide from Transgenic Mice with Human Immunoglobulin Loci

Abstract

To investigate the influence of antibody structure and specificity on antibody efficacy against Streptococcus pneumoniae, human monospecific antibodies (MAbs) to serotype 3 pneumococcal capsular polysaccharide (PPS-3) were generated from transgenic mice reconstituted with human immunoglobulin loci (XenoMouse mice) vaccinated with a PPS-3-tetanus toxoid conjugate and their molecular genetic structures, epitope specificities, and protective efficacies in normal and complement-deficient mice were determined. Nucleic acid sequence analysis of three MAbs (A7, 1A2, and 7C5) revealed that they use two different V H 3 genes (A7 and 1A2 both use V3-15) and three different V gene segments. The MAbs were found to have similar affinities for PPS-3 but different epitope specificities and CDR3 regions. Both A7 and 7C5 had a lysine at the V H -D junction, whereas 1A2 had a threonine. Challenge experiments with serotype 3 S. pneumoniae in BALB/c mice revealed that both 10-and 1-g doses of A7 and 7C5 were protective, while only a 10-g dose of 1A2 was protective. Both A7 and 7C5 were also protective in mice lacking either an intact alternative (FB ؊/؊ ) or classical (C4 ؊/؊ ) complement pathway, but 1A2 was not protective in either strain. Our data suggest that PPS-3 consists of epitopes that can elicit both highly protective and less protective antibodies and that the superior efficacies of certain antibodies may be a function of their structures and/or specificities. Further investigation of relationships between structure, specificity, and efficacy for defined MAbs to PPS may identify antibody features that might be useful surrogates for antibody (and vaccine) efficacy.

Depletion of Complement Has Distinct Effects on the Primary and Secondary Antibody Responses to a Conjugate of Pneumococcal Serotype 14 Capsular Polysaccharide and a T-Cell-Dependent Protein Carrier

“…Avidity was measured according to previously published methods (37) which have been used to measure avidity of antibodies to both pneumococcal (8) and nonpneumococcal (36) polysaccharides. Polystyrene 96-well plates (Nunc) were coated overnight at 4°C with 1 g of PPS14/ml.…”

“…The first was an ELISA-based assay (37) in which different concentrations of soluble PPS14 inhibited binding of anti-PPS14 IgG to solid-phase PPS14. This assay has previously been used to measure avidity of antibodies to pneumococcal polysaccharides (8). An avidity constant (␣K) was calculated as the inverse molar concentration of soluble PPS14 required to inhibit IgG binding by 50%.…”

A Peptide Mimotope of Type 8 Pneumococcal Capsular Polysaccharide Induces a Protective Immune Response in Mice

“…Unconjugated pneumococcal capsular polysaccharide vaccines elicit antibodies that are largely restricted in their immunoglobulin G (IgG) subclass distribution, with a preponderance of IgG2 in humans (IgG3 in mice), even after absorption of nonspecific antibodies (3,6,25,31,34,42,45,55). Type-specific antibodies to pneumococcal polysaccharide are also restricted in their V-region gene use, being predominantly derived from members of the V H 3 immunoglobulin gene family (1,13,39). Although the importance of antibody restriction for pneumococcal resistance is unknown, it may translate into a poor response to polysaccharide-based vaccines in patients with IgG subclass deficiencies and/or dysregulation of V H 3 gene expression, such as human immunodeficiency virus-infected individuals (1,11,12,47).…”

“…Despite the generation of protective human monoclonal antibodies (MAbs) to several pneumococcal capsular polysaccharides (9,13,43,46), the type-specific determinants that elicit protective antibodies are unknown. Since polysaccharides can elicit antibodies that are nonprotective (13,28), in addition to those that are protective, surrogates for certain polysaccharide antigens might be useful in focusing the immune response on "protective" epitopes, e.g., those that elicit only a protective response and/or overcome the restricted nature of the polysaccharide response (5,39).…”

Transgenèse animale et humanisation des anticorps

“…Ils ont ainsi permis de dériver un certain nombre d'anticorps de forte affinité et d'intérêt commercial important, reconnaissant aussi bien des petites molécules [15], des protéines spécifiques de pathogènes [16,17], des polysaccharides [18], des protéines humaines solubles et des cytokines comme l'interleukine-15 [19][20][21] ou membranaires comme l'antigène spécifique de prostate PSMA, le CD20, le CD30 ou le récepteur à l'EGF (epidermal growth factor) [22][23][24] et des antigènes associés à des tumeurs comme l'antigène carcinoembryonnaire [25]. Les premiers résultats à propos de tous ces Acm semblent très encourageants quant à leur faible immunogé-nicité chez l'homme (➜).…”