Uncovering the parasite and host determinants of Plasmodium vivax hypnozoite formation and development using single cell sequencing and human liver-chimeric mice

The human malaria-causing parasite Plasmodium vivax is geographically the most widespread of all the Plasmodium species. P. vivax is a major cause of morbidity in endemic regions of Asia, Oceania, Central and South America, as well as the horn of Africa. In these regions, P. vivax infections in pregnant women significantly contribute to early pregnancy loss, reduced birth weight and infant mortality. Notably, P. vivax is a major concern in an arena of malaria eradication due to its unique biology. Specifically, P. vivax sporozoite infectivity of hepatocytes does not always lead to the onset of schizogony and transition to blood stage disease, as is the case for P. falciparum. Rather, a sporozoite can enter a host hepatocyte, dedifferentiate and then lie dormant within the host hepatocyte for weeks, months or even years, before reactivating. This dormant or latent liver stage form is known as the hypnozoite and in continued efforts towards malaria elimination and eradication, the hypnozoite is a formidable foe. Indeed, the endemicity of P. vivax throughout tropical as well as temperate climate zones is attributed to the parasite’s ability to form hypnozoites, which after reactivating, case relapses of blood stage infection and concomitant transmission. Antimalarial drugs almost exclusively target the symptomatic blood stage of the life cycle and do not target the hypnozoite and thus treatment of P. vivax blood stage infections with standard drug regimens allows for further relapses and will not aid in disease eradication. Historically, the only approved drug active against P. vivax hypnozoites was primaquine although an improved 8-aminoquinoline drug, tafenoquine, has recently received approval for the treatment of relapsing malaria. Unfortunately, primaquine’s short half-life, long dosage regimen and incompatibility with glucose-6- phosphate dehydrogenase deficiency, prevent its use for mass elimination campaigns. Thus, there is a need for novel interventions that will negatively affect hypnozoite formation, survival and relapse. Thus, the research in this proposal aims to shed biological insight on the hypnozoite. This application aims to address three critical biological questions pertaining to P. vivax hypnozoite biology and answering these questions should aid in the discovery of novel interventions to prevent hypnozoite relapse and the continued spread of P. vivax disease. Specifically, are there intrinsic factors that are pre-programmed in the P. vivax sporozoite that determine its fate once it reaches the liver to become either a replicating schizont or a dormant hypnozoite? How does the dormant hypnozoite manipulate its host cell in order to maintain its long-term residency? Can we develop a model of hypnozoite relapse in order to gain insight into the triggers that promote hypnozoite reactivation? Using a human-liver chimeric mouse model alongside innovative methods of single cell isolation and transcriptional profiling, we hope to being to address these challenges.