Creation and preclinical evaluation of genetically attenuated malaria parasites arresting growth late in the liver

Abstract

Whole-sporozoite (WSp) malaria vaccines induce protective immune responses in animal malaria models and in humans. A recent clinical trial with a WSp vaccine comprising genetically attenuated parasites (GAP) which arrest growth early in the liver (PfSPZ-GA1), showed that GAPs can be safely administered to humans and immunogenicity is comparable to radiation-attenuated PfSPZ Vaccine. GAPs that arrest late in the liver stage (LA-GAP) have potential for increased potency as shown in rodent malaria models. Here we describe the generation of four putative P. falciparum LA-GAPs, generated by CRISPR/Cas9-mediated gene deletion. One out of four gene-deletion mutants produced sporozoites in sufficient numbers for further preclinical evaluation. This mutant, PfΔmei2, lacking the mei2-like RNA gene, showed late liver growth arrest in human liver-chimeric mice with human erythrocytes, absence of unwanted genetic alterations and sensitivity to antimalarial drugs. These features of PfΔmei2 make it a promising vaccine candidate, supporting further clinical evaluation. PfΔmei2 (GA2) has passed regulatory approval for safety and efficacy testing in humans based on the findings reported in this study.

Comparative analyses of functional antibody-mediated inhibition with anti-circumsporozoite monoclonal antibodies against transgenic Plasmodium berghei

“…Thus, it is necessary to elucidate how antibody-mediated inhibition in vitro translates into inhibition in vivo. To accomplish this, the study utilized two well-characterized transgenic lines ( Pb mCh-luc [ 53 ] and Pb-Pf CSP(r) [ 52 , 62 ]) and inhibitory anti-CSP monoclonal antibodies. The inhibition potential and concentration of mAbs 2A10 and 3D11 were validated by comparative analysis in a live sporozoite gliding assay (Fig.…”

Same, same but different: Exploring Plasmodium cell division during liver stage development

“…falciparum parasites [ 49 ] highlighting a crucial and conserved role of PlasMei2 for Plasmodium LS schizogony. Pf PlasMei2-deficient parasites are therefore considered as potential genetically attenuated parasites (GAPs) for human vaccination trials [ 49 , 74 ].…”

Malaria Vaccines: Progress to Date

“…Genetically attenuated parasites that arrest growth late in the liver have been shown in animal models to induce stronger protective immune responses than those that arrest earlier and this may be explained by exposure to a broader repertoire of parasite antigens [ 61 ]. Late liver stage-arresting replication-competent (LARC) P. falciparum GAPs have been developed by two different research groups through the targeted deletion of the Mei2 gene [ 62 , 63 ]. In both instances, the parasite does not produce exoerythrocytic merozoites, and this prevents initiation of the blood-stage infection.…”