Human liver organoids are susceptible to Plasmodium vivax infection.

Background: The eradication of Plasmodium vivax malaria is complicated due to the presence of hypnozoites, the hidden dormant form of the parasite that is present in the liver. Currently available drug regimens are effective at killing hypnozoites but cause side effects and are difficult to administer. Studies testing drugs for liver-stage malaria remain rare and mainly rely on the use of cancerous or immortalized hepatic cells and primary hepatocytes.

Methods: Organoids were used as platform to model liver-stage vivax malaria. Hepatic endoderm cells, endothelial progenitor cells and mesenchymal cells were generated from human induced pluripotent stem cells and self-assembled into liver organoids on top of Matrigel layer. Liver characteristic and maturity were examined through genes and proteins expression of liver markers, and liver functional tests before infected with Plasmodium vivax sporozoites. The infection was then verified by the detection of parasitophorous vacuole membrane proteins, Upregulated in Infectious Sporozoite 4 (UIS4), and blood-stage infection following co-culture with human reticulocytes.

Results: Generated liver organoids showed upregulation of liver specific transcripts including hepatic nuclear factor 4A (HNF4A), alpha-fetoprotein (AFP), and albumin (ALB) which also confirmed by the protein expression. Furthermore, those organoids resembled mature hepatocytes in terms of albumin secretion, fat and glycogen storage and cytochrome activity. Following invasion of P. vivax sporozoites, PvUIS4 was detected and the hepatic merozoites could develop into ring-stage and early trophozoites in human reticulocytes. Moreover, differential expression patterns of genes involved in lipid and cholesterol synthesis were also detected.

Conclusions: Stem cell-derived liver organoids resemble mature liver cells in terms of liver functions and are susceptible to infection with P. vivax sporozoites, paving the way for studies on the mechanism of hypnozoite formation and testing of possible hypnozoitocidal drugs.