Summary Mounting evidence supports the concept that Merkel cell polyomavirus (MCV) is a causal factor underlying most cases of a highly lethal form of skin cancer known as Merkel cell carcinoma. To explore the possibility that polyomaviruses commonly infect healthy human skin, we developed an improved rolling circle amplification (RCA) technique to isolate circular DNA viral genomes from skin swab specimens. Complete MCV genomes were recovered from 14/35 (40%) healthy adults, providing the first full-length, apparently wild-type cloned genomes for this polyomavirus species. RCA analysis also revealed the existence of two previously unknown polyomavirus species that we name human polyomavirus-6 (HPyV6) and HPyV7. Biochemical experiments show that polyomavirus DNA is shed from the skin in the form of assembled virions. A pilot serological study indicates that infection or co-infection with the three skin-tropic polyomaviruses is very common. Thus, at least three polyomavirus species are constituents of the human skin microbiome.

Merkel cell polyomavirus (MCV) has been implicated as a causative agent in Merkel cell carcinoma. Robust polyclonal antibody responses against MCV have been documented in human subjects, but monoclonal antibodies (mAbs) specific for the VP1 capsid protein have not yet been characterized. We generated 12 mAbs capable of binding recombinant MCV virus-like particles. The use of a short immunogenic priming schedule was important for production of the mAbs. Ten of the 12 mAbs were highly effective for immunofluorescent staining of cells expressing capsid proteins. An overlapping set of 10 mAbs were able to neutralize the infectivity of MCV-based reporter vectors, with 50% effective doses in the low picomolar range. Three mAbs interfered with the binding of MCV virus-like particles to cells. This panel of anti-capsid antibodies should provide a useful set of tools for the study of MCV.