Pseudovirions in the Study of Papilloma- and Polyomaviruses

Abstract: The papilloma- and polyomaviruses are small DNA viruses that infect humans. Some members of these virus families can cause cancer in experimental animals and some are also established as carcinogenic to humans. Detection of specific antibodies to these viruses allows tracking past and present infections to elucidate natural history and association of infection with subsequent disease. As there are more than 150 types of Human papillomaviruses (HPV) and at least 10 Human polyomaviruses (HPyV), the study of antibodies to these virus families require high-throughput methods. Although it is difficult to produce infectious virus stocks of these viruses, so-called pseudovirions that morphologically and immunologically resemble native virions but lack the viral genome can be produced in vitro. In the present thesis, we produced such pseudovirions and used them to i) delineate the importance of hypervariable surface loops for the antigenicity and biological function of the HPV particle ii) developed and validate serological assays for measuring specific antibodies to HPV and Merkel cell polyomavirus (MCPyV) and iii) perform prospective seroepidemio-logical studies to evaluate whether infection with MCPyV was associated with an increased risk for Merkel cell carcinoma. Site-directed mutagenesis of the surface loops of the HPV capsid found that these loops were essential for the incorporation of the minor capsid protein L2, the genome encapsidation and proper immunogenicity of the particle. Pseudovirion-based methods were correlated to presence of viral DNA. The pseudovirion neutralization assays and multiplexed assays using pseudovirions bound to heparin-coated fluorescent beads for 21 HPV and 2 HPyV types were correlated with viral DNA for 16 HPV types and MCPyV. MCPyV specific antibody levels in serum were found to be strongly correlated to the MCPyV viral load in skin. Finally, biobank-based seroepidemiological studies found that MCPyV infection was associated with an increased risk for Merkel cell carcinoma (MCC), in particular among females.