Delayed booster dosing improves human antigen-specific Ig and B cell responses to the RH5.1/AS01_B malaria vaccine

Abstract

BackgroundAntibodies are crucial for vaccine-mediated protection against many pathogens. Modifications to vaccine delivery that increase antibody magnitude, longevity, and/or quality are therefore of great interest for maximising efficacy. We have previously shown that a delayed fractional (DFx) dosing schedule (0-1-6mo) – using AS01B-adjuvanted RH5.1 malaria antigen – substantially improves serum IgG durability as compared to monthly dosing (0-1-2mo; NCT02927145). However, the underlying mechanism and whether there are wider immunological changes with DFx dosing was unclear.MethodsImmunokinetics of PfRH5-specific Ig across multiple isotypes were compared between DFx and monthly regimen vaccinees. Peak responses were characterised in-depth with a systems serology platform including biophysical and functional profiling. Computational modelling was used to define the humoral feature set associated with DFx dosing. PfRH5-specific B cells were quantified by flow cytometry and sorted for single cell RNA sequencing (scRNA-seq). Differential gene expression between DFx and monthly dosing regimens was explored with Seurat, DESeq2 and gene set enrichment analysis.ResultsDFx dosing increases the frequency of circulating PfRH5-specific B cells and longevity of PfRH5-specific IgG1, as well as other isotypes and subclasses. At the peak antibody response, DFx dosing was distinguished by a systems serology feature set comprising increased FcRn-binding, IgG avidity, and proportion of G2B and G2S2F IgG Fc glycans, alongside decreased IgG3, antibody-dependent complement deposition, and proportion of G1S1F IgG Fc glycan. At the same time point, scRNA-seq of PfRH5-specific B cells revealed enriched plasma cell and Ig / protein export signals in the monthly dosing group as compared to DFx vaccinees.ConclusionsDFx dosing of the RH5.1/AS01B vaccine had a profound impact on the humoral response. Our data suggest plausible mechanisms relating to improved FcRn-binding (known to improve Ig longevity) and a potential shift from short-lived to long-lived plasma cells. Recent reports of the positive impact of delayed boosting on SARS-CoV-2 vaccine immunogenicity highlight the broad relevance of these data.

Analyses of vaccine-specific circulating and bone marrow-resident B cell populations reveal benefit of delayed vaccine booster dosing with blood-stage malaria antigens

“…Next, B cells were stained with anti-human CD19-BV786 (563325, BD Biosciences), anti-human CD20-BUV395 (563782, BD Biosciences), anti-human IgG-BB515 (564581, BD Biosciences), anti-human IgM-BV605 (562977, BD Biosciences), anti-human CD27-PE-Cy7 (560609, BD Biosciences), anti-human CD21-BV711 (563163, BD Biosciences), anti-human CD38-BV480 (566137, BD Biosciences), anti-human CD138-APC-R700 (566050, BD Biosciences), anti-human IgA-PerCP-Vio700 (130-113-478, Miltenyi) as well as two fluorophore-conjugated DBPRII probes. Preparation of the DBPRII probes was based on our previously published protocols with the P. falciparum blood-stage malaria antigen RH5 [12; 20]. In brief, monobiotinylated DBPRII was produced by transient co-transfection of HEK293F cells with a plasmid encoding BirA biotin ligase and a plasmid encoding a monoFC-fused, biotin acceptor peptide-and c-tagged full-length DBPRII.…”

“…The B cell assay with cryopreserved samples from the RH5 clinical trial was performed as above with two modifications to the protocol. First, RH5 probes rather than DBPRII probes were used as previously described [12; 20]. Second, probe staining was repeated during the intracellular cytokine staining step at a 1/10 dilution as compared to concentrations used for surface staining.…”