Down-selection of the VAR2CSA DBL1-2 expressed in E. coli as a lead antigen for placental malaria vaccine development

Abstract

Over 50 million women are exposed to the risk of malaria during pregnancy every year. Malaria during pregnancy is a leading global cause of maternal morbidity and adverse pregnancy outcomes. Adhesion of Plasmodium falciparum-infected erythrocytes to placental chondroitin-4-sulfate (CSA) has been linked to the severe disease outcome of placental malaria. Accumulated evidence strongly supports VAR2CSA as the leading placental malaria vaccine candidate. Recombinant proteins encompassing the VAR2CSA high affinity CSA binding site have been generated, and their activity as immunogens that elicit functional (inhibitory) and cross-reactive antibodies against CSA-binding parasites assessed. The expression of His-tagged proteins was compared in four different expression systems and their capacity to bind specifically to CSA was analyzed. CHO cells and E. coli SHuffle cells were the two expression systems able to express some of the recombinant proteins in reasonable amounts. Larger analytical scale production of DBL1x-2× (3D7) and DBL3x-4ε (FCR3) best expressed in CHO and E. coli SHuffle cells were performed. Purified proteins were administered to rats either alone or adjuvanted with human approved adjuvants. Analysis of the functionality and cross-reactivity of the induced antibodies allowed us to down-select the DBL1x-2(3D7) expressed in E. coli SHuffle cells as the best antigen to be transitioned to further clinical development in order to protect future pregnant women living in malaria endemic areas against the severe clinical outcomes of placental malaria.

Preclinical immunogenicity and safety of the cGMP-grade placental malaria vaccine PRIMVAC

“…The design of the non-clinical toxicology study was performed according to the “Guidelines on the non-clinical evaluation of vaccine adjuvants and adjuvanted vaccines” [27]. Rats were chosen as it is a rodent species in which an immune response to the vaccine antigen VAR2CSA is developed and enhanced by the adjuvants Alhydrogel® and GLA-SE [24] through mechanisms expected to be similar than in humans. Three groups of 15 male and 15 female Sprague-Dawley rats received the vaccine candidate, PRIMVAC, at the dose-level of 110 μg/animal, alone (group 3) or adjuvanted with either Alhydrogel® (Brenntag, Denmark) at 0.85 mg/animal (group 4) or GLA-SE (Infectious Disease Research Institute, USA) at 5 μg/animal (group 5), by intramuscular injection, on Days 1, 15, 29 and 43.…”

“…Var2csa orthologues are conserved among parasite isolates and strains but the relatively high degree of protein sequence polymorphisms represents a challenge for vaccine design [20]. Nevertheless, several studies demonstrated that immunoglobulins from anti-sera raised against VAR2CSA recombinant proteins were able to recognize IEs from placental origins but also to block their adhesion to CSA [[21], [22], [23], [24]]. Taken together these studies suggest that VAR2CSA expressed by placental parasites possesses conserved antigenic determinants that are the target of antibodies.…”

“…Two placental malaria vaccine candidates (PRIMVAC and PAMVAC) are currently under clinical development [26]. The prophylactic vaccine candidate PRIMVAC is based on a CSA-binding DBL1x-2x multidomain of VAR2CSA from the P. falciparum 3D7 strain (DBL1x-2x (3D7) down-selected from a multi-system expression study [24]). The His-tagged DBL1x-2x (3D7) has been successfully expressed in E.coli SHuffle® in sufficient amount and with a degree of purity compatible for transition to cGMP production [24].…”

“…The prophylactic vaccine candidate PRIMVAC is based on a CSA-binding DBL1x-2x multidomain of VAR2CSA from the P. falciparum 3D7 strain (DBL1x-2x (3D7) down-selected from a multi-system expression study [24]). The His-tagged DBL1x-2x (3D7) has been successfully expressed in E.coli SHuffle® in sufficient amount and with a degree of purity compatible for transition to cGMP production [24]. When adjuvanted with Alhydrogel® or Glucopyranosyl Lipid A Adjuvant-Stable Emulsion (GLA-SE), DBL1x-2x (3D7) expressed in E. coli SHuffle® stood up as the best antigen able to generate antibodies that recognize IEs expressing different variants of VAR2CSA and block their adhesion to CSA [24].…”

The Delay in the Licensing of Protozoal Vaccines: A Comparative History

“…While this binding is responsible for the blood supply to the placenta, at the same time it increases the risk of babies with low birth weight. Currently, the research is focused on the development of a vaccine against conserved regions of the PfEMP protein in order to reduce Malaria in Sub Saharan Africa (66).…”