Controlled Human Malaria Infection reveals that the Dantu blood group variant provides high level protection against uncomplicated malaria

Abstract

AbstractIntroductionThe long co-evolution ofHomo sapiensandPlasmodium falciparumhas resulted in the selection of numerous human genetic variants that confer an advantage against severe malaria and death. One such variant is the Dantu blood group antigen, which is associated with 74% protection against severe and complicatedP. falciparummalaria infections in homozygous individuals, similar to that provided by the sickle haemoglobin allele (HbS). Recentin vitrostudies suggest that Dantu exerts this protection by increasing the surface tension of red blood cells, thereby impeding the ability ofP. falciparummerozoites to invade them and reducing parasite multiplication. However, no studies have yet explored this hypothesisin vivo.MethodsWe investigated the effect of Dantu on early phaseP. falciparum(Pf) infections in a controlled human malaria infection (CHMI) study. 141 sickle negative Kenyan adults were inoculated with 3.2×103aseptic, purified, cryopreserved Pf sporozoites (PfSPZ Challenge) then monitored for blood-stage parasitaemia for 21 days by quantitative polymerase chain reaction (qPCR) analysis of the 18S ribosomal RNAP. falciparumgene. The primary endpoint was blood-stageP. falciparumparasitaemia of ≥500/μl while the secondary endpoint was the receipt of antimalarial treatment in the presence of parasitaemia of any density. On study completion, all participants were genotyped both for Dantu and for four other polymorphisms that are associated with protection against severe falciparum malaria: α+-thalassaemia, blood group O, G6PD deficiency, and the rs4951074 allele in the red cell calcium transporterATP2B4.ResultsThe primary endpoint was reached in 25/111 (22.5%) non-Dantu subjects, in comparison to 0/27 (0%) Dantu heterozygotes and 0/3 (0.0%) Dantu homozygotes (p=0.01). Similarly, 49/111 (44.1%) non-Dantu subjects reached the secondary endpoint in comparison to only 7/27 (25.9%) and none of the 3 (0.0%) Dantu heterozygotes and homozygotes respectively (P=0.021). No significant impacts on either outcome were seen for any of the other variants under study.ConclusionThis study reveals, for the first time, that the Dantu blood group is associated with high level protection against early, non-clinical,P. falciparummalaria infectionsin vivo. Learning more about the mechanisms involved could potentially lead to new approaches to the prevention or treatment of the disease. Our study illustrates the power of CHMI with PfSPZ Challenge for directly testing the protective impact of genotypes previously identified using other methods.