探討PD-L1對腫瘤進展之影響

Study of The Functional Roles of PD-L1 in Tumor Progression

洪精樺(Jing-Hua Hung)

指導教授 ： 吳漢忠

國立臺灣大學/醫學院/病理學研究所/碩士(2017年)

https://doi.org/10.6342/NTU201701756

摘要

免疫檢查點（immune checkpoint）所造成的免疫抑制（immunosuppression）以迴避免疫系統的攻擊是癌症的特徵之一。癌細胞能夠表現許多種免疫抑制的訊號造成免疫細胞失去功能甚至凋亡。這些傳遞抑制訊號的分子之中，PD-L1能夠與T細胞、B細胞、樹突狀細胞以及自然殺手細胞等免疫細胞所表現的PD-1結合，進而削弱免疫系統對抗癌症的功能。然而，PD-L1對癌細胞所造成的生物性功能之影響仍有待進一步釐清。在本研究中，我們透過西方點墨法以及即時聚合酶連鎖反應挑選出高度及低度表達PD-L1的人類肺癌細胞株（H441）和胰臟癌細胞株（BxPC3），建立PD-L1靜默或過度表達之細胞株，進而觀察細胞功能性。我們發現隨著PD-L1含量增加，細胞的增生、遷移、侵襲以及集落形成的能力將會顯著地提升。同時，在人類肺癌細胞異種移植的免疫缺陷型小鼠中也觀察到腫瘤生長能力符合活體外的實驗結果。基於人類PD-L1與老鼠PD-1能跨物種結合，我們以慢病毒感染小鼠腸癌細胞株（CT26），建立過度表達人類PD-L1的小鼠癌細胞，並且在免疫健全小鼠中建立同種移植以及肺轉移模型，得知PD-L1可促使癌細胞轉移，並發現PD-L1與腫瘤血管新生（angiogenesis）具有關聯性。綜合以上結果，PD-L1對於癌症本身即具有促進腫瘤進展之能力，而這些特性將有希望成為重要的癌症治療對策。

關鍵字

免疫檢查點 ； PD-L1 ； 血管新生 ； 轉移

並列摘要

Immunosuppression is one of the hallmarks of cancer, which allows cancer cells to escape immune checkpoint-initiated attacks. Cancer cells can express many molecules that inhibit immune signaling, causing loss of function or even apoptosis in immune cells. One of these inhibitory molecules, programmed cell death ligand-1 (PD-L1), suppresses the anti-cancer function of several immune cell types by binding to programmed cell death protein-1 (PD-1), which is present on the surface of T cells, B cells, dendritic cells, and natural killer cells. Whether PD-L1 plays additional roles in the biological functioning of cancer cells is still unknown. In this study, we measured PD-L1 expression in cancer cell lines derived from human lung cancer (H441) or pancreatic cancer (BxPC3) by Western blotting and qPCR. Then, we established stable cell lines, in which PD-L1 was knocked down or overexpressed, and investigated the tumorigenic function. We found that proliferation, migration, invasion, and colony formation ability were elevated in cells that had high PD-L1 expression. Consistent with these in vitro results, tumor growth in a lung cancer xenograft immunodeficient mouse model was also increased by high PD-L1 expression. Because human PD-L1 has high binding affinity for mouse PD-1, we used lentivirus to overexpress human PD-L1 in a mouse colon cancer cell line (CT26). These cells were then used in a syngeneic tumor model and lung metastasis model in immunocompetent mice. We found that PD-L1 can enhance cancer cell metastasis, and is also associated with tumor angiogenesis. Taken together, the data show that PD-L1 exhibits innate oncogenic functions in tumor cells, and blocking these effects could prove to be an important therapeutic strategy in multiple cancer types.

並列關鍵字

immune checkpoint ； PD-L1 ； angiogenesis ； metastasis

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