The Honorine Ward Lab
Cryptosporidium - Host Interactions
The majority of our research is focused on the apicomplexan parasite Cryptosporidium which causes diarrheal disease in humans worldwide. Cryptosporidiosis is asymptomatic or self-limiting in immunocompetent hosts but may be severe, persistent and life threatening in immunocompromised patients, such as those with untreated acquired immunodeficiency syndrome (AIDS) or young children in resource-limited settings. Cryptosporidium has caused several outbreaks of waterborne disease worldwide. Because of the potential for intentional contamination of water supplies, Cryptosporidium is listed as a Category B Priority Pathogen for Biodefense by the Centers for Disease Control.
Nitazoxanide is the only drug approved in the USA by the Food and Drug Administration for use in immunocompetent individuals with cryptosporidiosis. However, this drug is not effective against cryptosporidiosis in immunocompromised hosts. There is currently no vaccine available for cryptosporidiosis. Therefore, the continued search for novel preventive and therapeutic strategies is critical.
The pathogenic mechanisms by which C. parvum causes disease are poorly understood. In addition, little is known about specific parasite and host molecules involved in host-parasite interactions or about protective innate and adaptive immune responses to infection in humans. Our overall goal in the study of cryptosporidiosis is to further our understanding of the molecular basis of Cryptosporidium-host cell interactions and to investigate immune responses to this parasite. Understanding the molecular mechanisms underlying the host-parasite interaction may lead to the development of specific interventions targeted at inhibiting this interaction. Identifying the mechanisms underlying protective immunity could lead to the development of immune-based preventive and therapeutic anti-cryptosporidial strategies.
Most laboratory studies of Cryptosporidium use in vitro models of transformed intestinal epithelial cell lines to study host-parasite interactions. However, these cells do not support growth and development of the parasite for longer than 3-5 days and do not accurately recapitulate human intestinal structure and function. Currently, in collaboration with Dr. Mary Estes at Baylor College of Medicine and Dr. David Kaplan at Tufts School of Engineering we are using novel 2D and 3D in vitro and ex vivo models of novel bioengineered intestinal tissue models employing stem-cell derived human intestinal enteroids (HIE) obtained from surgical or endoscopic human intestinal biopsies. These HIE can be cultured for 8 weeks or more and support robust infection of Cryptosporidium (Fig. 1) We are using these models to investigate host responses to infection, including innate immune responses and to profile host and parasite transcriptomes.
Figure 1. Fig 1: C. parvum infection in 3D bioengineered human stem-cell derived intestinal enteroid-based model a and b: uninfected areas c to l: intracellular stages.
In addition, we are studying the role of parasite mucin-type glycoproteins and glycan binding proteins in mediating attachment to and invasion of host IEC. These include gp40, gp15, gp900, p30 and CpClec. In collaboration with Dr. Boris Striepen at the University of Pennsylvania, we are using CRISPR Cas-9 based technology to generate transgenic parasites in which the genes of interest are deleted or tagged in order to study their function. We are also studying polypeptide-N-acetylgalactosaminyl transferases which catalyze the synthesis of O-glycan residues on mucin-type glycoproteins. The long-term goal is to determine whether these glycoproteins or the enzymes which post-translationally modify them may serve as targets of drug or vaccine development.
Global Health Studies of Infectious Diarrhea and Malnutrition
In collaboration with international investigators we are conducting cross sectional and longitudinal studies of infectious diarrheal diseases, particularly cryptosporidiosis in children in resource-limited settings. We are investigating systemic and mucosal Cryptosporidium-specific humoral and cell-mediated immune responses to specific antigens which are putative vaccine candidates in these children. In other studies, we are investigating the role of the intestinal microbiota in childhood diarrhea, malnutrition and environmental enteric dysfunction. The long-term goal of these studies is the logical development of interventions such as vaccines and therapeutics that are appropriate to the communities in which the burden of these diseases is greatest.