Human Parvovirus B19: from the development of a reverse genetics system to antiviral strategies

Human Parvovirus B19 (B19V) is a human pathogenic virus and responsible for various clinical manifestations, although neither an antiviral therapy nor a vaccine are available. Difficulties for B19V propagation and characterization are caused by its narrow tropism for the erythroid progenitor cells of human bone marrow and the very few cell lines that can support the viral replication. In this research, a reverse genetic approach was first developed to allow the generation of mature and infectious viral particles from a designed viral consensus sequence. Synthetic clones that differ for their terminal regions (ITRs) were constructed, transfected in UT7/EpoS1 cells and the obtained viral particles were used to infect EPCs (erythroid progenitor cells) in serial passages. Mature and functional viral particles were obtained by clones containing the almost full length ITRs and by clones codifying shorter ITRs, extended till the internal symmetry sites but with different sequence isomerisms. Cellular factors and machinery change along the eryhroid differentiation probably influencing and delimiting the cellular susceptibility and permissiveness to the virus. In face of the limited fraction of B19V productively infected cells, the expression of the globoside receptor, the coreceptor, the endocytosis and the EpoR pathway was commonly detected among both EPCs and UT7/EpoS1 cells during this research, suggesting the involvement of other cellular factors. Characterization of both the virus and cells allows investigation of new strategies for the development of specific antiviral compounds. In this research, the retargeted drug Hydroxyurea and especially the broad range analogue Brincidofovir showed a B19V antiviral activity. Small-scale screening of newly synthesized molecules led to identification of few compounds with suboptimal activity. The computational predictions of G-quadruplex structures within the B19V ITRs was not corroborated by chemical and biological studies excluding any their relevant role in the viral lifecyle.