A Plasmodium berghei sporozoite-based vaccination platform against human malaria

Abstract

There is a pressing need for safe and highly effective Plasmodium falciparum (Pf) malaria vaccines. The circumsporozoite protein (CS), expressed on sporozoites and during early hepatic stages, is a leading target vaccine candidate, but clinical efficacy has been modest so far. Conversely, whole-sporozoite (WSp) vaccines have consistently shown high levels of sterilizing immunity and constitute a promising approach to effective immunization against malaria. Here, we describe a novel WSp malaria vaccine that employs transgenic sporozoites of rodent P. berghei (Pb) parasites as cross-species immunizing agents and as platforms for expression and delivery of PfCS (PbVac). We show that both wild-type Pb and PbVac sporozoites unabatedly infect and develop in human hepatocytes while unable to establish an infection in human red blood cells. In a rabbit model, similarly susceptible to Pb hepatic but not blood infection, we show that PbVac elicits cross-species cellular immune responses, as well as PfCS-specific antibodies that efficiently inhibit Pf sporozoite liver invasion in human hepatocytes and in mice with humanized livers. Thus, PbVac is safe and induces functional immune responses in preclinical studies, warranting clinical testing and development.

The PHIST protein GEXP02 targets the host cytoskeleton during sexual development of Plasmodium falciparum

“…Primary human hepatocytes were incubated with either 10,000 sporozoites for traversal (Yang et al, 2017) or 50,000 sporozoites (Mendes et al, 2018) per well as previously described from both the knockout and parental line. The SMFA was prepared using 1-ml gametocyte culture that was added to 600 μl of washed packed RBCs.…”

“…The SMFA was prepared using 1-ml gametocyte culture that was added to 600 μl of washed packed RBCs. For the invasion assay, infected hepatocytes were fixed in and permeabilised and detected with 3SP2-FITC antibodies (Mendes et al, 2018) and counted by flow cytometry. Samples were added to prewarmed glass feeding devices, and 100-150 laboratory raised female mosquitoes were allowed to feed for 10 min.…”

“…NF54 wt and the NF54/GEXP02-KO parasites lines were allowed to passage through mosquitoes (as described above) with slavery gland sporozoites collected on Day 15. Primary human hepatocytes were incubated with either 10,000 sporozoites for traversal (Yang et al, 2017) or 50,000 sporozoites (Mendes et al, 2018) per well as previously described from both the knockout and parental line. Briefly, sporozoites for the traversal assay were incubated in conjunction with fluorescein isothiocyanate (FITC)-dextran and positive (traversed) hepatocytes counted via flow cytometry (Yang et al, 2017).…”

“…Briefly, sporozoites for the traversal assay were incubated in conjunction with fluorescein isothiocyanate (FITC)-dextran and positive (traversed) hepatocytes counted via flow cytometry (Yang et al, 2017). For the invasion assay, infected hepatocytes were fixed in and permeabilised and detected with 3SP2-FITC antibodies (Mendes et al, 2018) and counted by flow cytometry.…”

Strains used in whole organism Plasmodium falciparum vaccine trials differ in genome structure, sequence, and immunogenic potential

“…Of these vaccine candidates, Sanaria® PfSPZ vaccine, based on radiationattenuated sporozoites, has progressed furthest in clinical trial testing [3][4][5][6][7][8][9]. Other whole-organism vaccine candidates, including chemoattenuated (Sanaria® PfSPZ-CVac), transgenic, and genetically attenuated sporozoites, are in earlier stages of development [10][11][12].…”