A replication-competent late liver stage–attenuated human malaria parasite
Debashree Goswami, … , Ashley M. Vaughan, Stefan H.I. Kappe
Debashree Goswami, … , Ashley M. Vaughan, Stefan H.I. Kappe
Published June 2, 2020
Citation Information: JCI Insight. 2020;5(13):e135589. https://doi.org/10.1172/jci.insight.135589.
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Research Article Infectious disease Vaccines

A replication-competent late liver stage–attenuated human malaria parasite

Abstract

Whole-sporozoite vaccines engender sterilizing immunity against malaria in animal models and importantly, in humans. Gene editing allows for the removal of specific parasite genes, enabling generation of genetically attenuated parasite (GAP) strains for vaccination. Using rodent malaria parasites, we have previously shown that late liver stage–arresting replication-competent (LARC) GAPs confer superior protection when compared with early liver stage–arresting replication-deficient GAPs and radiation-attenuated sporozoites. However, generating a LARC GAP in the human malaria parasite Plasmodium falciparum (P. falciparum) has been challenging. Here, we report the generation and characterization of a likely unprecedented P. falciparum LARC GAP generated by targeted gene deletion of the Mei2 gene: P. falciparum mei2–. Robust exoerythrocytic schizogony with extensive cell growth and DNA replication was observed for P. falciparum mei2– liver stages in human liver-chimeric mice. However, P. falciparum mei2– liver stages failed to complete development and did not form infectious exoerythrocytic merozoites, thereby preventing their transition to asexual blood stage infection. Therefore, P. falciparum mei2– is a replication-competent, attenuated human malaria parasite strain with potentially increased potency, useful for vaccination to protect against P. falciparum malaria infection.

Authors

Debashree Goswami, William Betz, Navin K. Locham, Chaitra Parthiban, Carolyn Brager, Carola Schäfer, Nelly Camargo, Thao Nguyen, Spencer Y. Kennedy, Sean C. Murphy, Ashley M. Vaughan, Stefan H.I. Kappe

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Figure 4

P. falciparum mei2– liver stages display late defects in exoerythrocytic schizogony.

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P. falciparum mei2– liver stages display late defects in exoerythrocyti...
P. falciparum NF54 and P. falciparum mei2– sporozoites were injected intravenously into FRG NOD huHep mice, and infected liver tissue sections were used for measuring parasite size by IFA and parasite rRNA load by 18S rRNA quantitative real-time PCR (qRT-PCR). (A) Comparison of the size of late liver stage parasites (based on area at the parasite’s largest circumference) between P. falciparum NF54 (gray) and P. falciparum mei2– (red) on days 6 and 7 postinfection. P. falciparum NF54 liver stages are significantly larger than P. falciparum mei2– on day 7. Data represent mean ± SD. n = at least 12 schizonts per time point. Statistical analysis was carried out using 2-way ANOVA using Tukey’s multiple comparison test. P values are indicated in the graph. P > 0.05 is taken as ns. (B) Analysis of parasite liver load by 18S rRNA qRT-PCR was carried out on extracted RNA from P. falciparum NF54–infected (gray) and P. falciparum mei2––infected (red) livers on day 6 and 7 postinfection, depicted as log10 copies of P. falciparum 18S rRNA/μg of extracted liver RNA. Data represent mean ± SD. n = 3 mice per time point. Statistical analysis was carried out using 2-way ANOVA using Holm-Šídák multiple comparison test. P values are indicated in the graph. P > 0.05 is taken as ns.