Correlation of Molecular Characteristics, Isotype, and In Vitro Functional Activity of Human Antipneumococcal Monoclonal Antibodies

Abstract

Structure-function correlations of pneumococcal antibodies are important in predicting how changes in the pneumococcus (Pnc)-specific B-cell repertoire will influence humoral immunity against invasive Pnc disease. Using a unique panel of human hybridomas derived from memory B cells after pneumococcal conjugate vaccination, we analyzed the structure-function relationship of nine monoclonal antibodies (MAbs) reactive to Pnc polysaccharides. The avidities of the antibodies correlated with the avidity of donor immune serum (R, 0.7; P < 0.025), and this relationship was particularly strong for immunoglobulin A clones (R, 1; P < 0.0005), suggesting that the MAbs may represent important clones contributing to serological memory. Common heavy-light chain combinations and amino acid replacement mutations were seen for clones with the same serospecificity from different individuals. The two highest-avidity MAbs used Vh3-48, and two MAbs with the same serospecificity, using the same V gene pairings (Vh3-7 and Vk2A17), had similar avidities, suggesting that canonical V gene use makes an important contribution to avidity. Although all clones had mutation levels consistent with their being derived from memory B cells, low levels of replacement mutation were associated with high avidities. This relationship was strongest for Vh genes (R, 0.8; P < 0.01). Opsonophagocytosis was demonstrated for all clones, and there was a trend toward clones using canonical genes with low levels of mutation having high opsonophagocytic activities (R, 0.5). These data suggest that the use of canonical genes in the Pnc antibody response is associated with highly functional antibodies and that most somatic mutations seen in these genes are not antigen selected.Understanding the molecular diversity of the antibody response to polysaccharide antigens has assumed increasing importance with the development of protein-polysaccharide conjugate vaccines that are immunogenic and protect those who are unable to respond to pure polysaccharide vaccines. Many studies have focused on responses to the capsular polysaccharides derived from Haemophilus influenzae type b (Hib), and these studies have demonstrated an oligoclonal antibody (Ab) response with between one and four immunoglobulin (Ig) variable-region (V) genes dominating the Ab repertoire to a specific polysaccharide (2, 25). Similar heavy-chain variable-region genes have been shown to be used by different individuals, and particular V genes appear to be associated with superior functional activity in vitro (24,26). A number of factors have been shown to influence antigen-specific V gene dominance, including the age of the individual (3), the dose of antigen (18), and the vaccine formulation (24). It is now becoming clear that the choice of V-region gene during a primary immune response may be critical, as this Vregion gene use may dominate subsequent memory responses. A murine study by Sanchez et al. demonstrated that the V gene repertoire induced during the initial priming stage of a T-dependent antige...

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

“…The requirement for neutrophils, but not complement, when a higher dose of 7A9 was used and the requirement for complement when a lower dose was used suggest there could be a dichotomy between Fc and complement receptors in 7A9-mediated antipneumococcal activity, depending on the amount of antibody. More work is needed to determine whether 7A9-and/or 5F6-like antibodies are produced in response to PPS3 vaccination in humans, but it is worth noting that 5F6-like antibodies would not be identified by the standard opsonophagocytosis assay, because it includes a complement source (5,68). Nonetheless, 5F6-like antibodies might be useful when complement is scarce, as it can be in the setting of pneumococcal infection and sepsis (73).…”

Fully human monoclonal antibodies from antibody secreting cells after vaccination with Pneumovax®23 are serotype specific and facilitate opsonophagocytosis

“…Although human monoclonal antibodies to S. pneumoniae have been produced in the past (Baxendale and Goldblatt, 2006; Baxendale et al, 2000; Zhou et al, 2002; Zhou et al, 2004), these previous studies have been limited by two factors: one, they employed Fab expression library screens and two, they employed random production of hybridomas. In addition, previous studies have either focused on one serotype (6B and 23F) or have utilized vaccination with the conjugate vaccine Prevnar that consists of only seven capsular serotypes.…”

Somatic Diversity in CDR3 Loops Allows Single V-Genes To Encode Innate Immunological Memories for Multiple Pathogens

“…The human Ab response to PPS is oligoclonal, and anti-PPS Abs repeatedly use a limited range of V-genes (4,5). Abs against the 23F serotype of S. pneumoniae frequently use IGKV2-24 or IGKV3-11 for the L chain and IGHV3-30 for the H chain (6).…”