Microorganisms 9, 1394 (2021)

Microorganisms 9, 1394 (2021). whereas the Vi-TT primary followed by the Vi-PS boost induced IgG1 and IgG2 antibody production. B cells from recipients who received both primary and boost showed evidence of convergence, with shared V gene usage and CDR3 characteristics. The detected Vi antibodies showed heterogeneous avidity ranging from 10 M to 500 pM, with no evidence of VX-787 (Pimodivir) affinity maturation after the boost. Vi-specific antibodies mediated Fc effector functions, which correlated with antibody dissociation kinetics but not with association kinetics. We identified antibodies induced by primary and boost vaccines that VX-787 (Pimodivir) acknowledged subdominant epitopes, indicated by binding to the deCTyphi Vi and enriching for antibody Fc functions that protect against typhoid fever will advance the design of high-efficacy Vi vaccines for protection across diverse populations. INTRODUCTION Vaccines are designed to induce a protective immune response against pathogens through the induction of functional antibodies (1). Correlates or surrogates of protection are often based on antibody levels (e.g., type b, hepatitis B vaccines) (2), although in many cases, protective antibody thresholds are difficult to reproduce. Few vaccines have mechanistic correlates, such as those measured in a serum bactericidal assay (e.g., meningococcal vaccines) or opsonophagocytosis assay (e.g., pneumococcal vaccines) (1, 3). Hence, increased attention is needed on not only the quantity but also the quality of the antibody response. Where quantitative antibody features fail, qualitative features such as specificity and affinity play a crucial role in protection against various pathogens including HIV-1, malaria, Zika, as well as others (4C7). In addition, antibody repertoire sequencing and single-cell B cell receptor (BCR) sequencing have provided insight into antibody development and selection upon immunization. Studying antibody responses after immunization and contamination is therefore important to determine the antibody specificities that impart protection or control and, ultimately, for the development and optimization of vaccines. One of the more recently developed vaccines for the prevention of typhoid fever is usually a Vi typhoid conjugate vaccine (Vi-TCV), in which Vi capsular polysaccharide antigen (Vi PS) is usually conjugated to tetanus toxoid (Vi-TT). Vi-TT induces immune responses that target Vi PS of subspecies serovar Typhi (Typhi) (8). This bacterial pathogen infects 10 million to 13 million people annually (9) and is evolving to display extensive antibiotic resistance (10, 11). Immunogenicity of Vi-TT was established in a non-endemic populace VX-787 (Pimodivir) using a controlled human contamination model (CHIM), where the efficacy was found to be comparable to the licensed plain Vi PS vaccine (Vi-PS) (12). After this, a Vi-TT efficacy of 82% was observed in a randomized, controlled trial in typhoid-endemic Nepal (13). Both studies reported an increase in anti-Vi immunoglobulin G (IgG) antibodies after immunization; however, estimates on thresholds of Vi IgG required for protection have been difficult to reproduce for decades (14, 15). Recently, we reported that Vi PSCspecific IgG1 avidity and IgA magnitude and fold change were associated with protection in a CHIM study (16, 17). Although Vi vaccination is usually widely used to protect against typhoid fever, data on repertoire and functionality of antibodies induced after Vi immunization are currently limited. Understanding how to broaden the specificities and functional antibody repertoire will inform further immunogen design to protect against typhoid fever. The Vi PS antigen constitutes one of the major virulence factors of Typhi as it shields the bacterial cell from the innate immune system upon entry VX-787 (Pimodivir) through the gastrointestinal tract (18, 19). The Vi PS antigen is usually a linear homopolymer of ?14-galacturonic acid with variable Typhi) at the C3 position and a fixed = 3) and 7 days after boost with Vi-PS (= 8) were used VX-787 (Pimodivir) for single-cell BCR sequencing (fig. S1). Humoral responses measured after Vi-PS boost represent both memory B cell responses induced by the Vi-TT primary in addition to na?ve B cell responses induced by the Vi-PS boost. Because Ig subclasses are major Rabbit Polyclonal to DDX51 determinants of antibody functionality, we investigated the subclass distribution within identified BCRs. After Vi-TT primary immunization, the predominant subclass was IgG1 (81.9 to 86.5%), with a small percentage of IgG2 (10.2 to 15.9%). In the paired samples after the Vi-PS boost, IgG1 (50.1 to 65.6%) remained the most prevalent, but increased percentages of IgG2 antibodies (28.1 to 46.5%) were observed. IgG2 sequences were also prevalent in the.