Characterization of Functional Human Monoclonal Antibody to Plasmodium vivax Duffy Binding Protein from Malaria Exposed Individuals from Brazilian Amazon

Background: Plasmodium vivax merozoites recognize specific receptors on the host cell surface to selectively invade reticulocytes. A critical parasite ligand is the domain II of Duffy binding protein (PvDBPII) that binds specifically to an erythrocyte membrane glycoprotein, namely Duffy antigen/receptor for chemokines (DARC). Materials and Methods: We have previously found naturally acquired antibodies that inhibited PvDBPII binding to DARC by >80% in 26.6% of rural Amazonians exposed to low malaria endemicity. These high-level binding-inhibitory antibodies (BIAbs) were predominantly PvDBPII variant-transcending and reduced by >40% the risk of clinical vivax malaria during the follow-up. Here, we sorted single PvDBPII-specific IgG+ memory B cells from two of these individuals with high-level BIAb responses, PCR amplified their IgG heavy and light chain variable regions, and cloned them into a human IgG expression vector to generate a panel of human monoclonal antibodies (MoAbs). Results: One of these MoAbs (#134/135) recognized PvDBPII in ELISA and inhibited PvDBPII binding to FY*AFY*A erythrocytes more efficiently than FY*BFY*Berythrocytes (100% and 92.8%, inhibition, respectively). We next used competition ELISA to test whether naturally acquired antibodies from 170 plasma samples with high levels of BIAbs targeted the same epitope(s) recognized by MoAb. Antibodies in 70% of these samples blocked MoAb binding to PvDBP by >90%, consistent with recognition of the same or similar epitope(s). Conclusions: After conclude that is MoAB recognizes PvDBPII by ELISA and inhibits the interaction between PvDBPII and DARC, we are now focusing in test whether this MoAB is able to block P. vivaxinvasion of reticulocytes in vitro, using a cryopreserved parasites.