HPV16-E7-Specific Activated CD8 T Cells in E7 Transgenic Skin and Skin Grafts

Abstract

Human papillomavirus (HPV) 16 E7 (E7) protein expression in skin promotes epithelial hyperproliferation and transformation to malignancy. Grafts of murine skin expressing E7 protein as a transgene in keratinocytes are not rejected from immunocompetent recipients, whereas grafts expressing ovalbumin (OVA), with or without coexpression of E7 protein, are promptly rejected, demonstrating that E7-associated non-antigen-specific local immunosuppression is not a major determinant of lack of rejection of E7 transgenic skin. To determine whether failure of rejection of E7 skin grafts is due to failure to attract E7-specific effector T cells, E7- and OVA-specific effector CD8+ T cells, activated in vitro, were transferred to animals bearing E7 transgenic skin grafts. Three days after T cell transfer, E7-specific T cells were present in significantly greater numbers than OVA-specific T cells in the grafted skin on animals bearing recently placed or healed E7 grafts, without graft rejection, and also in the ear skin of E7 transgenic animals, without obvious pathology. E7 and OVA-specific T cells were present in lesser numbers in healed E7 grafts than in recently placed grafts and in lesser numbers in recently placed E7 transgenic epidermal grafts without E7-associated hyperproliferation, derived from E7 transgenic mice with a mutated retinoblastoma gene. These data demonstrate that effector T cells are to some extent attracted to E7 transgenic skin specifically by E7 expression, but in large measure non-specifically by the epithelial proliferation associated with E7 expression, and by the local inflammation produced by grafting. Failure of E7 graft rejection was observed despite trafficking of E7-specific effector T cells to E7-expressing epithelium, a finding of consequence for immunotherapy of HPV 16 E7-associated human cancers.

Murine HPV16 E7-expressing transgenic skin effectively emulates the cellular and molecular features of human high-grade squamous intraepithelial lesions

“…We hypothesise that these factors, when present in the K14E7 skin environment, co-ordinately induce ineffective CD8 effector T cell responses against K14E7 skin grafts. More recently, the overarching hypothesis has been refined in that E7-induced hyperplasia rather than expression of E7, is responsible for the recruitment, programming and/or retention of these immunosuppressive cells and molecules in the K14E7 hyperplastic epithelium milieu, as mice expressing E7 protein from the Keratin 14 promoter, and with a mutated retinoblastoma protein that is functionally effective but cannot bind E7, have no hyperplasia and no inflammatory infiltrates [20] , [31] , [89] . Hyperplastic murine K14E7 transgenic skin thus models some important aspects of the cellular infiltrate and immunosuppressive cytokine secretion profile in cervical cancer and high-grade CIN lesions in human patients.…”

Recruitment of Antigen Presenting Cells to Skin Draining Lymph Node From HPV16E7-Expressing Skin Requires E7-Rb Interaction

“…Previously, we have demonstrated that activated antigen-specific CD8 T cells can enter both hyperplastic (K14.E7) and normoplastic (K14.E7xRb ΔL/ΔL ) E7-expressing epidermis but only a very low number of antigen-specific T cells are retained in the K14.E7xRb ΔL/ΔL epidermis (20). Graft rejection requires effector T cells to engage antigen expressing keratinocytes.…”

The Role of CXCR3 and Its Chemokine Ligands in Skin Disease and Cancer

“…Intracellular binding of E7 to the retinoblastoma (Rb) protein leads to a dysregulated cell cycle within keratinocytes and the subsequent development of a precancerous, hyperplastic epithelium resembling actinic keratosis, a precursor lesion which can progress to squamous cell carcinoma in human patients ( 143 ). One feature of the E7-driven hyperplasia is a chronic inflammatory/wound healing microenvironment associated with elevated levels of IFN-γ and immune cell infiltration ( 144 , 145 ). Chronic IFN-γ production in the skin, from cells such as infiltrating NKT cells, results in an immunosuppressed microenvironment via mediators such as IDO ( 146 – 148 ).…”