A replication-competent late liver stage–attenuated human malaria parasite
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
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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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 8

Experimental design for testing P. falciparum mei2– liver stage breakthrough to blood stage patency.

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Experimental design for testing P. falciparum mei2– liver stage breakthr...
(A) Schematic represents the experimental setup for results shown in Table 1 and in Supplemental Figure 8A. One million sporozoites from P. falciparum NF54 or P. falciparum mei2– clone F2 were injected into 2 and 4 FRG NOD huHep mice, respectively. Mice were repopulated with human RBCs as depicted, and blood samples were removed for parasite 18S rRNA qRT-PCR on days 7 through 10. Blood samples from days 7 and 10 were transferred to in vitro culture for up to 10 days posttransition. (B) Schematic represents the experimental setup for results shown in Table 2 and in Supplemental Figure 8B. One million sporozoites from P. falciparum NF54 and P. falciparum mei2– clones F2 and F5 were injected into 2, 2, and 4 FRG NOD huHep mice, respectively. Mice were repopulated with human RBCs as depicted, and 50 μL blood was collected from all mice for parasite 18S rRNA qRT-PCR samples on day 7. One mouse infected with P. falciparum NF54, 1 mouse infected with P. falciparum mei2– clone F2, and 3 mice infected with P. falciparum mei2– clone F5 were exsanguinated on day 7, and blood was transferred to in vitro culture. The remaining mice infected with each clone were sacrificed on day 8 and processed for 18S rRNA qRT-PCR and in vitro culture. All in vitro culture samples were maintained for up to 8 weeks.