Topical Application of Houttuynia cordata Thunb Ethanol Extracts Increases Tumor Infiltrating CD8+ /Treg Cells Ratio and Inhibits Cutaneous Squamous Cell Carcinoma in vivo

Houttuynia cordata Thunb (HCT) is a medicinal and edible herb that has beneficial effects on various diseases dueto its diuretic, anti-inflammatory, anti-oxidative, anti-microbial, anti-viral, anti-cancer and anti-diabetic properties. Most reports of its anti-cancer activity were conducted in vitro, and its effects on cutaneous squamous cellcarcinoma (SCC) have not been investigated yet. Using DMBA/TPA induced SCC mice model, we found thattopical treatment by HCT, as well as its bioactive ingredient monomer, efficiently inhibited tumor growth.Mechanistically, tumor infiltrating CD⁴⁺, Foxp³⁺ T regulatory cells (Tregs) were significantly reduced andCD⁸⁺/Treg cells ratio was largely increased in tumors after HCT treatment. In addition, several chemokineswhich function to recruit immune cells were largely reduced in SCC cancer cells treated by HCT in vitro. Ourresults demonstrate the therapeutic effects of HCT on cutaneous SCC and indicate it might inhibit cancer throughregulating tumor infiltrating lymphocytes and the tumor immune microenvironments.