title: Pre-existing Fas ligand (FasL) in cancer cells elicits tumor-specific protective immunity, but delayed induction of FasL expression after inoculation facilitates tumor formation.
abstract: Overexpression of Fas ligand (FasL) in cancer cells elicits potential antitumor effects via recruitment of neutrophils. Conversely, FasL-expressing tumors may counterattack tumor-infiltrating lymphocytes by delivering apoptotic death signals via Fas/FasL interactions, which may lead to tumor escape. In order to distinguish the role of FasL in antitumor activity and tumor progression, Lewis lung carcinoma cells (LLC-1) were used to establish the cell line LLC-FasL, in which FasL expression was repressed by doxycycline (Dox) treatment and induced in the absence of Dox. LLC-FasL cells promote tumor regression when expressing FasL, whereas tumor outgrowth is observed by depletion of FasL expression. To investigate whether initial expression of FasL during tumor formation is critical for FasL-mediated tumor regression, Dox-treated LLC-FasL cells were inoculated into Dox-treated mice, but Dox treatment was stopped 5 days after inoculation. When low cell numbers were inoculated, we observed 80% survival and no tumor formation, whereas no mice survived inoculation with high cell numbers, despite the delayed induction of FasL by Dox withdrawal. The inoculation of a high density of cells may establish a favorable tumor microenvironment before the expression of FasL. Our findings demonstrate that FasL may elicit antitumor activity when it is initially present on injected cancer cells and thus can act prior to tumor microenvironment formation. Furthermore, a well-established tumor microenvironment abrogates FasL-mediated antitumor activity.
authors.affiliation: Institute of Bioscience and Biotechnology and Center of Excellence for Marine Bioenvironment and Biotechnology (CMBB), National Taiwan Ocean University, Keelung, Taiwan, ROC.
authors.forename: Hsiao-Ying
authors.initials: HY
authors.lastname: Chiu
authors.forename: Guang-Huan
authors.initials: GH
authors.lastname: Sun
authors.forename: Shiow-Yi
authors.initials: SY
authors.lastname: Chen
authors.forename: Hsiao-Hsien
authors.initials: HH
authors.lastname: Wang
authors.forename: Ming-Yi
authors.initials: MY
authors.lastname: Ho
authors.forename: Chia-Yi
authors.initials: CY
authors.lastname: Chu
authors.forename: Wan-Lin
authors.initials: WL
authors.lastname: Wu
authors.forename: Ren-Shiang
authors.initials: RS
authors.lastname: Jhou
authors.forename: Yi-Lin
authors.initials: YL
authors.lastname: Tsai
authors.forename: Rui-Ting
authors.initials: RT
authors.lastname: Huang
authors.forename: Kuang-Hui
authors.initials: KH
authors.lastname: Sun
authors.forename: Shye-Jye
authors.initials: SJ
authors.lastname: Tang
mesh_terms: D000818:Animals; D045744:Cell Line, Tumor; D002471:Cell Transformation, Neoplastic / Q000187:drug effects / Q000235:genetics* / Q000276:immunology* / Q000378:metabolism; D004318:Doxycycline / Q000494:pharmacology; D053222:Fas Ligand Protein / Q000096:biosynthesis / Q000235:genetics* / Q000276:immunology* / Q000378:metabolism; D006801:Humans; D019169:Jurkat Cells; D008297:Male; D008546:Melanoma, Experimental / Q000235:genetics* / Q000276:immunology* / Q000378:metabolism / Q000473:pathology; D051379:Mice; D008810:Mice, Inbred C57BL; D059016:Tumor Microenvironment / Q000187:drug effects / Q000235:genetics* / Q000276:immunology
chemical_list: D053222:Fas Ligand Protein; D004318:Doxycycline