Plasma antimalarial antibody can mediate anti-parasite immunity but has not previously been characterized at the molecular level. Here, we develop an innovative strategy to characterize humoral responses by integrating profiles of plasma immunoglobulins (IG) or antibodies with those expressed on B cells as part of BcR. We applied this strategy to define plasma IG and determine variable V gene usage after vaccination with the Plasmodium falciparum zygote antigen Pfs25. First, using proteomic tools coupled with bulk immunosequencing data, we determined human F(ab’)2 peptide sequences from plasma IG of adults who received four doses of Pfs25-EPA/Alhydrogel. Specifically, Pfs25 antigen-specific F(ab’)2 peptides (Pfs25-IG) were aligned to cDNA sequences of IGH complementarity determining region 3 (CDR3) from a dataset generated by total peripheral B cell immunosequencing of the entire vaccinated population. IGHV4 was the most commonly identified IGHV subgroup of Pfs25-IG, a pattern that was corroborated by VH/VL sequencing of Pfs25-specific single B cells from five vaccinees and by matching plasma Pfs25-IG peptides and V-(D)-J sequences of Pfs25-specific single B cells from the same donor. Among 13 recombinant human mAbs generated from IG sequences of Pfs25-specific single B cells, a single IGHV4 mAb displayed strong neutralizing activity, reducing the number of P. falciparum oocysts in infected mosquitoes by more than 80% at 100 μg/mL. Our approach characterizes the human plasma antibody repertoire in response to the Pfs25-EPA/Alhydrogel vaccine and will be useful to study circulating antibodies in response to other vaccines as well as those induced during infections or autoimmune disorders.

References

PubMed