in vitro modelling of BPV1 infection

Papillomaviruses (PVs) are small DNA viruses that can induce benign lesions or cancer disease in vertebrates. For example, several human PVs are the causative agents of head-and-neck and anogenital squamous cell carcinomas as well as cervical cancer in humans. PVs are usually species-specific and have a pronounced tropism for epithelial keratinocytes. The small subgroup of Delta-PVs are an exception to this rule. The can also infect dermal fibroblasts and, perhaps for this reason, have a broader host range. This is best demonstrated for the bovine Delta-PV type 1, which infects cattle but also horses and other equid species, where it causes locally aggressive skin tumours termed sarcoids. Sarcoids develop in up to 12% of equids worldwide, are highly therapy-resistant and significantly reduce or annul the sales value of affected animals. Hence, the disease is of high veterinary and economic relevance. Although BPV1 is the best-studied animal PV, the mechanisms underllying (i) initial infection, and (ii) the spread of infection wthin the equid host are completely unknown. Based on our preliminary data, we postulate that, unlike other PVs, BPV1 does not necessarily require the environment of basal keratinocytes for initial infection of horse skin, but can directly infect equine fibroblasts. We further hypothesize that extracellular vesicles have a major role in the propagation of BPV1 within the infected equid host. We propose to test these hypotheses in innovative near-natural in vitro models that we have recently established. One model consists of equine primary fibroblasts stably infected with wild-type BPV1 particles (2D-model). The other consists of equine skin spheroids, that is a matrix of BPV1-infected or non-infected fibroblasts surrounded by equine primary keratinocytes (3D-model) mimicking the dermal and the epidermal layers of skin.