Induced pluripotent stem cell-derived human macrophages as an infection model for Leishmania donovani

The parasite Leishmania donovani is one of the species causing visceral leishmaniasis in humans, a deadly infection claiming up to 40,000 lives each year. The current drugs for leishmaniasis treatment have severe drawbacks and there is an urgent need to find new anti-leishmanial compounds. However, the search for drug candidates is complicated by the intracellular lifestyle of Leishmania. Here, we investigate the use of human induced pluripotent stem cell (iPS)-derived macrophages (iMACs) as host cells for L. donovani. iMACs obtained through embryoid body differentiation were infected with L. donovani promastigotes, and high-content imaging techniques were used to optimise the iMACs seeding density and multiplicity of infection, allowing us to reach infection rates up to 70% five days after infection. IC50 values obtained for miltefosine and amphotericin B using the infected iMACs or mouse peritoneal macrophages as host cells were comparable and in agreement with the literature, showing the potential of iMACs as an infection model for drug screening. Author SummaryYearly, up two million people in poverty-stricken areas contract leishmaniasis, a disease caused by parasites of the genus Leishmania. When an infected sandfly takes a blood meal, Leishmania parasites enter the host where they are taken up by macrophages. Inside the macrophage, Leishmania parasites establish a niche where they can proliferate. Although this infection often leads to disability or death, the drugs currently available are lacking due to toxic side effects, high expenses or difficulties in usage. Drug screening assays that are currently used for compound screening often rely on mouse peritoneal macrophages. We have generated human induced pluripotent stem cell derived macrophages and used these as new host cells for Leishmania donovani in the testing of anti-leishmanial compounds. This model has many advantages. For one, it allows us to work with human cells, mimicking the natural infection more closely than possible with murine cells. Secondly, it allows to obtain bigger batches of uniform cells for screening campaigns. Finally, this approach aligns with the principle of 3R, replacing the use of animals for cultivation of Leishmania and drug screening purposes.