Controlled human malaria infection by intramuscular and direct venous inoculation of cryopreserved Plasmodium falciparum sporozoites in malaria-naïve volunteers: effect of injection volume and dose on infectivity rates

Abstract

BackgroundControlled human malaria infection (CHMI) by mosquito bite is a powerful tool for evaluation of vaccines and drugs against Plasmodium falciparum malaria. However, only a small number of research centres have the facilities required to perform such studies. CHMI by needle and syringe could help to accelerate the development of anti-malaria interventions by enabling centres worldwide to employ CHMI.MethodsAn open-label CHMI study was performed with aseptic, purified, cryopreserved P. falciparum sporozoites (PfSPZ Challenge) in 36 malaria naïve volunteers. In part A, the effect of the inoculation volume was assessed: 18 participants were injected intramuscularly (IM) with a dose of 2,500 PfSPZ divided into two injections of 10 µL (n = 6), 50 µL (n = 6) or 250 µL (n = 6), respectively. In part B, the injection volume that resulted in highest infectivity rates in part A (10 µL) was used to formulate IM doses of 25,000 PfSPZ (n = 6) and 75,000 PfSPZ (n = 6) divided into two 10-µL injections. Results from a parallel trial led to the decision to add a positive control group (n = 6), each volunteer receiving 3,200 PfSPZ in a single 500-µL injection by direct venous inoculation (DVI).ResultsFour/six participants in the 10-µL group, 1/6 in the 50-µL group and 2/6 in the 250-µL group developed parasitaemia. Geometric mean (GM) pre-patent periods were 13.9, 14.0 and 15.0 days, respectively. Six/six (100%) participants developed parasitaemia in the 25,000 and 75,000 PfSPZ IM and 3,200 PfSPZ DVI groups. GM pre-patent periods were 12.2, 11.4 and 11.4 days, respectively. Injection of PfSPZ Challenge was well tolerated and safe in all groups.ConclusionsIM injection of 75,000 PfSPZ and DVI injection of 3,200 PfSPZ resulted in infection rates and pre-patent periods comparable to the bite of five PfSPZ-infected mosquitoes. Remarkably, it required 23.4-fold more PfSPZ administered IM than DVI to achieve the same parasite kinetics. These results allow for translation of CHMI from research to routine use, and inoculation of PfSPZ by IM and DVI regimens.Trial registration: ClinicalTrials.gov NCT01771848.Electronic supplementary materialThe online version of this article (doi:10.1186/s12936-015-0817-x) contains supplementary material, which is available to authorized users.

Expression of the Plasmodium falciparum Clonally Variant clag3 Genes in Human Infections

“…Approval for the controlled human malaria infection (CHMI) trial has been previously described [30]. All participants provided written informed consent before enrollment.…”

“…We also analyzed blood samples collected from volunteers participating in a CHMI study [30]. Additional details of sample collection and processing are provided in the Supplementary Methods.…”

“…We analyzed clag3 expression patterns in parasites collected from human volunteers participating in a CHMI trial [30] in which cryopreserved sporozoites of the culture-adapted line NF54 (from which 3D7 was derived) were used for infection ( Figure 4A). In samples collected from 6 different volunteers when parasites were first detected by microscopy (ie, on the day of malaria diagnosis [12-15 days after injection]), we observed higher levels of clag3.2 transcripts, compared with clag3.1, in contrast to the parental NF54 line used to infect the mosquitoes that almost exclusively expresses clag3.1 ( Figure 4B).…”

Current therapies and future possibilities for drug development against liver-stage malaria

“…Other models also exist to support the development of human-infective Plasmodium species, such as P. vivax or P. falciparum, in HepG2 and HC04 hepatoma cell lines, respectively (77,78). However, such studies are more challenging because of the lower infection rates of these parasites (79,80) and the restricted accessibility of these Plasmodium species, requiring access to facilities able to breed mosquitoes infected with these human-infective Plasmodium parasites or cryopreserved Plasmodium species sporozoites (81)(82)(83). Indeed, few research institutes have insectaries that are able to breed human-infective parasites in mosquitoes.…”

Development of whole sporozoite malaria vaccines

“…route gave 100% infectivity using 3,200 PfSPZ in a single 500-μL dose with a prepatent period similar to five-bite CHMI [95]. In other trials, 100% infectivity and prepatent periods comparable to five-bite CHMI were achieved using 3,200 PfSPZ administered i.v., 75,000 PfSPZ administered i.m., or 50,000 PfSPZ administered in eight 10 μL doses [96,97]; therefore the i.m. route required 23.4 times more PfSPZ than the DVI route.…”