Norovirus (NV) gastroenteritis is a major contributor to global morbidity and mortality, yet little is known about NV immunity and no effective vaccine exists. The recent discovery of murine noroviruses (MNV) a new genogroup of natural enteric mouse pathogens capable of growth in tissue culture has helped establish a key role for T cells in NV clearance. Despite these advances, a number of important questions remain, including: (1) what are the dynamics of T cell differentiation during norovirus infection~ and, (2) why do certain strains of norovirus persist in immunocompetent hosts? To address these questions we have identified novel immunodominant T cell epitopes and have constructed MHC-peptide tetramers. These new tools have allowed us, for the first time, to track MNV-specific T cell subsets and their functional properties. Based on preliminary results, we hypothesize that, in addition to being essential for initial clearance of infection, epitope- speciic T cell subsets in the intestinal mucosa can provide broad and long-lasting norovirus immunity~ conversely, loss of MNV-specific T cell function (exhaustion) in some settings leads to pathogen persistence. This hypothesis will be pursued by the following interrelated Specific Aims. (1) What are the dynamics of MNV-specific T cell differentiation, and where are T cells primed? Immunity to mucosal infection requires unique T cell differentiation states and priming mechanisms. First, using tetramer reagents, we will directly track and enumerate epitope-specific effector and memory T cells following mucosal vs. systemic infection. Second, we will use adoptive transfer to define the protective capacity of MNV-specific T cell subsets primed by mucosal vs. peripheral route. (2) Can dendritic cell (DC) vaccination induce robust T cell immunity to norovirus? Current norovirus vaccines result in weak T cell responses and this may be caused by failure of VLPs to recruit specific DC subsets necessary for mucosal T cell priming. To address this possibility, DCs from intestinal vs. peripheral sites will be exposed to immunodominant MNV T cell epitopes, and used to vaccinate na?ve mice. First, we will define the properties of MNV-specific T cells from DC- immunized animals before and after rechallenge. Second, we will use therapeutic DC vaccination to treat persistent MNV infection. These experiments will interface with Aims 1 and 3 by defining DC correlates of protective T cell immunity. (3) What are the differentiation states and protective properties of MNV- specific T cells that arise during persistent infection? Certain norovirus strains establish long-term infection. First, we will test whether T cell dysfunction occurs during persistent MNV infection by defining the phenotype, function, and protective capacity of MNV-specific CD4 and CD8 T cells from chronically vs. acutely infected mice. Second, we will define the reversibly of MNV-specific T cell exhaustion by using immunologic and genetic methods to selectively disrupt key inhibitory pathways. These innovative in vivo studies will provide mechanistic insights into the role of T cells in MNV infection, and serve as a platform for therapeutic strategies.

Public Health Relevance

Noroviruses are major contributors to global disease. In preliminary experiments using the murine norovirus model of infectious enteritis we have defined highly conserved immunodominant T cell epitopes and have constructed MHC-peptide tetramer reagents. We propose to use these new molecular tools to (1) define the role of T cell immunity during norovirus infection~ (2) explore novel vaccination approaches~ and (3) define immune mechanisms leading to persistent norovirus infection.

National Institute of Health (NIH)
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Clinical Investigator Award (CIA) (K08)
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Diabetes, Endocrinology and Metabolic Diseases B Subcommittee (DDK)
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Podskalny, Judith M,
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University of Pennsylvania
Internal Medicine/Medicine
Schools of Medicine
United States
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Osborne, Lisa C; Monticelli, Laurel A; Nice, Timothy J et al. (2014) Coinfection. Virus-helminth coinfection reveals a microbiota-independent mechanism of immunomodulation. Science 345:578-82
Tomov, Vesselin T; Osborne, Lisa C; Dolfi, Douglas V et al. (2013) Persistent enteric murine norovirus infection is associated with functionally suboptimal virus-specific CD8 T cell responses. J Virol 87:7015-31