Oncogenic high-risk HPV infections can cause transformation of healthy epithelium into pre-cancerous hyperproliferative epithelial lesions with potential to progress to cancer, due to persistent expression of the E6 and E7 viral oncoprotein. Transgenic mice expressing the HPV16-E7 (K14E7) oncoprotein in keratinocytes provide an experimental model for studying the effects of epithelial hyperplasia on the immune compartment. K14E7 skin is tolerated when grafted onto immunocompetent recipients despite the expression of E7 as neoantigen, and this tolerance is associated with mechanisms of immune suppression.
Skin resident antigen-presenting cells (APCs) comprise a heterogeneous population of immune cells indispensable in the coordination of the immune response to infection, inflammation, and cancer, and we developed a high-parameter flow cytometry panel to characterise the myeloid cell landscape in K14E7 epidermis. The panel delineates B cells, T cells, plasmacytoid dendritic cells (pDCs), Langerhans cells (LCs), neutrophils, and multiple cell states of monocytes, macrophages, and conventional dendritic cells (cDCs). Additionally, the panel enables the analysis of functional co-stimulatory and co-inhibitory features across these different cell subsets and states.
We found that K14E7 epithelium contains increased numbers and infiltration of myeloid cells into the epidermis including monocytes, pDCs, macrophages, and DCs. LCs displayed an altered phenotype with reduced MHCII and CD11b expression. Unbiased bioinformatic clustering determined previously unappreciated additional cell state heterogeneity. Many myeloid cells expressed increased levels of CD86, indicating an increased state of maturation, and differential expression of PD-L1.