Fig. 4

Evidence for stability of artemisinin resistance. a Following cryopreservation of resistant parasites with unchanged IC₅₀: parasitemia trends from mice infected with the ART-R₃₀ strain following cryopreservation and cultivation in vitro are shown. Arrows indicate day of re-challenge with 30 mg/kg AS. b Following cryopreservation of parasites with increased IC₅₀: parasitemia trends from animals infected with ART-R₁₂₀ (orange) and ART-R₂₄₀ (purple, pink) following cryopreservation and cultivation in vitro. Arrows indicate the day of re-challenge with either 120 or 240 mg/kg artesunate (AS). c In vitro response following in vivo replication without drug pressure: In vitro sensitivities for AS and dihydroartemisinin (DHA) measured for ART-R₁₂₀ parasites grown ex vivo, that were sampled before and after 1 month of drug pressure-free in vivo replication (see d), are tabulated. d In vivo following drug free replication: We maintained the ART-R₁₂₀ parasite in vivo for 4 weeks without drug pressure in three mice; parasitemia trends of the two mice that survived are shown (red, blue). Challenges performed before and after treatment with 120 mg/kg AS (arrows) show stability of the resistant phenotype. We employed a lower intensity huRBC grafting protocol for this experiment to increase mouse survival, which caused a drop in parasitemia in the interim