Development and evaluation of a new Plasmodium falciparum 3D7 blood stage malaria cell bank for use in malaria volunteer infection studies

Abstract

Background: New anti-malarial therapeutics are required to counter the threat of increasing drug resistance. Malaria volunteer infection studies (VIS), particularly the induced blood stage malaria (IBSM) model, play a key role in accelerating anti-malarial drug development. Supply of the reference 3D7-V2 Plasmodium falciparum malaria cell bank (MCB) is limited. This study aimed to develop a new MCB, and compare the safety and infectivity of this MCB with the existing 3D7-V2 MCB, in a VIS. A second bank (3D7-V1) developed in 1995 was also evaluated.

Methods: The 3D7-V2 MCB was expanded in vitro using a bioreactor to produce a new MCB designated 3D7-MBE-008. This bank and 3D7-V1 were then evaluated using the IBSM model, where healthy participants were intravenously inoculated with blood-stage parasites. Participants were treated with artemether-lumefantrine when parasitaemia or clinical thresholds were reached. Safety, infectivity and parasite growth and clearance were evaluated.

Results: The in vitro expansion of 3D7-V2 produced 200 vials of the 3D7-MBE-008 MCB, with a parasitaemia of 4.3%. This compares to 0.1% in the existing 3D7-V2 MCB, and < 0.01% in the 3D7-V1 MCB. All four participants (two per MCB) developed detectable P. falciparum infection after inoculation with approximately 2800 parasites. For the 3D7-MBE-008 MCB, the parasite multiplication rate of 48 h (PMR₄₈) using non-linear mixed effects modelling was 34.6 (95% CI 18.5-64.6), similar to the parental 3D7-V2 line; parasitaemia in both participants exceeded 10,000/mL by day 8. Growth of the 3D7-V1 was slower (PMR₄₈ of 11.5 [95% CI 8.5-15.6]), with parasitaemia exceeding 10,000 parasites/mL on days 10 and 8.5. Rapid parasite clearance followed artemether-lumefantrine treatment in all four participants, with clearance half-lives of 4.01 and 4.06 (weighted mean 4.04 [95% CI 3.61-4.57]) hours for 3D7-MBE-008 and 4.11 and 4.52 (weighted mean 4.31 [95% CI 4.16-4.47]) hours for 3D7-V1. A total of 59 adverse events occurred; most were of mild severity with three being severe in the 3D7-MBE-008 study.

Conclusion: The safety, growth and clearance profiles of the expanded 3D7-MBE-008 MCB closely resemble that of its parent, indicating its suitability for future studies.

Trial registration: Australian New Zealand Clinical Trials registry numbers: P3487 (3D7-V1): ACTRN12619001085167. P3491 (3D7-MBE-008): ACTRN12619001079134.

Keywords: CHMI; Induced blood-stage malaria; Malaria; Plasmodium falciparum; VIS.

Fig. 1

Study Design. In both studies, participants were inoculated with approximately 2800 infected erythrocytes on Day 0, followed by artemether-lumefantrine treatment when threshold parasitaemia was reached (> 10,000 parasites/mL). The participants were confined for 3 days, during which they were treated with artemether-lumefantrine. The last study visit occurred on Day 90 ± 2. For the 3D7-V1 study, the confinement period occurred between Day 10–13 (Panel a). For the 3D7-MBE-008 study, the confinement period commenced on Day 8 (Panel b)

Fig. 2

Parasite growth and clearance after artemether-lumefantrine (AL) treatment Parasitaemia from Day 4 to Day 60 for the 3D7-MBE-008 study (Panel a). Parasitaemia from Day 4 to Day 60 for the 3D7-V1 study (Panel b). The vertical dashed lines represent the administration of artemether-lumefantrine treatment