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 7

P.falciparum mei2– liver stages display defects in DNA replication and segregation.

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P.falciparum mei2– liver stages display defects in DNA replication and ...
(A) An analysis of nuclear DNA centers based on DAPI staining between NF54 and P. falciparum mei2– liver stages on day 7. Scale bar: 7 μm. (B) The graph shows the total number of nuclear centers per late liver stage schizont. Fewer nuclear centers are observed in P. falciparum mei2– (red) in comparison with P. falciparum NF54 (gray), indicating incomplete DNA segregation. Data represent mean ± SD. n = 7 liver stage schizonts. Statistical analysis was carried out using an unpaired t test. P > 0.05 is taken as ns. (C) The graph shows the volume of each nuclear center. The average volume per nuclear center was calculated for each schizont (day 7). P. falciparum mei2– (red) nuclear centers are smaller in comparison with P. falciparum NF54 (black), indicating less DNA content in P. falciparum mei2–. These results indicate a defect in DNA replication and segregation. Data represent mean ± SD. n = 7 liver stage schizonts. Statistical analysis was carried out using an unpaired 2-tailed t test. P value is mentioned in the graph. P > 0.05 is taken as ns.