Immunization with Recombinant Plasmodium falciparum Erythrocyte Membrane Protein 1 CIDRα1 Domains Induces Domain Subtype Inhibitory Antibodies

Abstract

malaria pathogenesis is tied to the sequestration of parasites in the microvasculature. Parasite sequestration leading to severe malaria is mediated by erythrocyte membrane protein 1 (PfEMP1) binding to endothelial protein C receptor (EPCR) via its CIDRα1 domains. CIDRα1 domains are targets of naturally acquired immunity, and a vaccine eliciting antibodies inhibiting the EPCR binding of CIDRα1 could potentially prevent disease and death from malaria. CIDRα1 domains have diversified in sequence to escape immune recognition but preserved structure to maintain EPCR binding. The EPCR-binding CIDRα1 domains separate into six major sequence types predicted to form a conserved structure in which only the amino acids essential for EPCR binding are highly conserved. Here, we investigated whether antibodies elicited by vaccination with single or multiple recombinant CIDRα1 domains are able to bind and inhibit diverse CIDRα1 domains. We found that EPCR binding-inhibitory antibodies to CIDRα1 variants closely related to those used for vaccination are readily elicited, whereas antibodies binding distant CIDRα1 variants are sporadically generated and are rarely inhibitory. Despite this, sequence similarity correlated poorly with the ability of induced antibodies to inhibit across diverse variants, and no continuous sequence regions of importance for cross-inhibitory antibodies could be identified. This suggested that epitopes of cross-variant inhibitory antibodies were predominantly conformational. Vaccination with immunogens engineered to focus immune responses to specific epitopes or an optimal choice of multiple CIDRα1 variants may improve elicitation of broadly reactive and inhibitory antibody responses.

Modified MHC Class II–Associated Invariant Chain Induces Increased Antibody Responses againstPlasmodium falciparumAntigens after Adenoviral Vaccination

“…Using the Ii-fur adjuvant, we could show that the Ab response was not only increased to the encoded Ags but also to heterologous CIDRa1 proteins. The breadth of reactivity of elicited Abs to inhibit CIDRa1 variants not included in the vaccination was similar to what was observed in a recent study vaccinating with recombinant CIDRa1 proteins (63).…”

Immunization with virus-like particles conjugated to CIDRα1 domain of Plasmodium falciparum erythrocyte membrane protein 1 induces inhibitory antibodies

“…In the present study, CIDRα1.4 immunization readily produced antibodies inhibiting the EPCR-binding of the CIDRα1.4 variant present in the vaccines as well as other CIDRα1 variants typically within the same subgroup as the immunogen. This was also seen in previous studies [27,28], where animals were vaccinated with soluble recombinant CIDRα1 domains or live attenuated adenovirus inducing in vivo CIDRα1 protein secretion. In these studies, induction of cross-reactive antibodies was most clearly demonstrated by vaccination using two CIDRα1.1 domains resulting in antibodies reactive to 11 of 14 group B/A (CIDRα1.1 and CIDRα1.8) antigen variants [27].…”

“…Serum levels of antigen specific IgG were measured as previously described [31]. In brief, plates were coated with 5 µg/mL 30 kDa HIS-tagged HB3var03 CIDRα1.4 protein [28]. The wells were blocked with 1% BSA buffer.…”

“…Experimental immunization of mice and rats with single or multiple soluble CIDRα1 proteins, or adenovirus inducing in vivo secretion of CIDRα1 protein, readily elicit EPCR binding-inhibitory IgG to cognate antigens, as well as to CIDRα1 variants of the same CIDRα1 subtype as the used immunogen [27,28]. The most heterogeneous of CIDRα1 subtypes is the CIDRα1.4 and CIDRα1.7 domains, to which it appears to be particularly difficult to elicit cross-ractive antibodies.…”

Longitudinal analysis of naturally acquired PfEMP1 CIDR domain variant antibodies identifies associations with malaria protection

“…Transcripts encoding CIDRα1.7 domains have been found to predominate among the most severe cases of pediatric cerebral malaria -those that lead to brain swelling and death (19). The immunodominance of CIDRα1.7(c) may be a consequence of epitopes targeted by cross-reactive CIDRα1 antibodies (41,42). Moreover, PfEMP1 with CIDRα1.4 and CIDRα1.7 domains frequently contain ICAM1-binding DBLβ domains (43).…”