Intestinal organoid/enteroid-based models for Cryptosporidium

Cryptosporidium is a leading cause of diarrhea and death in young children and untreated AIDS patients in resource-poor settings, and of waterborne outbreaks of disease in developed countries. However, there is no consistently effective treatment for vulnerable populations. Progress towards development of therapeutics for cryptosporidiosis has been hampered by lack of optimal culture systems to study it. New advances in organoid/enteroid technology have contributed to improved platforms to culture and propagate Cryptosporidium. Here we discuss recent breakthroughs in the field and highlight different models for functional ex vivo organoid or enteroidderived culture systems. These systems will lead to a better understanding of the mechanisms of host-parasite interactions in vivo.

Two- and Three-Dimensional Bioengineered Human Intestinal Tissue Models for Cryptosporidium

Conventional cell cultures utilizing transformed or immortalized cell lines or primary human epithelial cells have played a fundamental role in furthering our understanding of Cryptosporidium infection. However, they remain inadequate with respect to their inability to emulate in vivo conditions, support long-term growth, and complete the life cycle of the parasite. Previously, we developed a 3D silk scaffold-based model using transformed human intestinal epithelial cells (IECs). This model supported C. parvum infection for up to 2 weeks and resulted in completion of the life cycle of the parasite. However, transformed IECs are not representative of primary human IEC.Human intestinal enteroids (HIEs) are cultures derived from crypts that contain Lgr5+ stem cells isolated from human biopsies or surgical intestinal tissues; these established multicellular cultures can be induced to differentiate into enterocytes, enteroendocrine cells, goblet cells, Paneth cells, and tuft cells. HIEs better represent human intestinal structure and function than immortalized IEC lines. Recently, significant progress has been made in the development of technologies to culture HIEs in vitro. When grown in a 3D matrix, HIEs provide a spatial organization resembling the native human intestinal epithelium. Additionally, they can be dissociated and grown as monolayers in tissue culture plates, permeable supports or silk scaffolds that enable mechanistic studies of pathogen infections. They can also be co-cultured with other human cells such as macrophages and myofibroblasts. The HIEs grown in these novel culture systems recapitulate the physiology, the 3D architecture, and functional diversity of native intestinal epithelium and provide a powerful and promising new tool to study Cryptosporidium-host cell interactions and screen for interventions ex vivo. In this chapter, we describe the 3D silk scaffold-based model using transformed IEC co-cultured with human intestinal myofibroblasts and 2D and 3D HIE-derived models of Cryptosporidium, also co-cultured with human intestinal myofibroblasts.

Cellular Basis for Reduced Resistance in DBA/2 Mice to Babesia microti

The protozoan parasites Babesia bovis, divergens and microti infect humans and other mammals via the tick Ixodus Scapularis. Babesia causes a malaria-like hemolytic disease with the most severe cases seen in those who are immunocompromised or over the age of 50. Mice offer the opportunity to understand genetic and age-related differences in resistance to infection. Previously, we showed that two month old DBA/2 mice are less resistant to Babesia than BALB/cByJ. Further, unlike BALB/cByJ mice, 18 month old DBA/2 mice are not able to clear their infections. Cell transfers established that these differences were at least in part due to CD4 T cell intrinsic differences. We hypothesized that DBA’s relative susceptibility might be due to an inability to produce sufficient cytokines. We harvested the splenocytes of infected young BALB/c and DBA/2 mice at days 7 to 24 post infection and measured the percentage and total number of cytokine-producing T cells. BALB/c mice have more CD4 and CD8 T-cells than infected DBA/2 mice. They also have many more cells with cytoplasmic IFN-y, IL-21 and IL-17A. However, the median fluorescence intensity of cytokine staining and the frequencies of cytokine positive cells did not differ between strains. Thus, the absolute difference in cytokine-positive cell numbers was due to the expansion of the activated T cell populations. In vitro activation revealed that in response to anti CD3 antibody, T cells of DBA/2 mice were less responsive. A similar phenotype might explain why individuals over the age of 50 are more susceptible to severe babesiosis.