B細胞的清除導致B型肝炎的復發──從臨床觀察到動物模式建立

Abstract

B型肝炎是藉由B型肝炎病毒所引起的感染性疾病，現今全球約有兩億五千萬人受到慢性B型肝炎的纏身，最終可能引發肝硬化或甚至肝癌導致死亡。目前已有疫苗，可以有效預防感染B型肝炎病毒，但在藥物治療上卻無法完全根除深植於細胞核中，B型肝炎病毒的去氧核糖核苷酸，使患者需長期服用干擾素或類核苷酸藥物。此外近20年越來越多臨床案例指出，當B型肝炎患者同時帶有B細胞淋巴癌時，並針對淋巴瘤給予抗癌藥物以及免疫抑制劑時，往往會再度活化HBV，提升病患慢性肝衰竭急性發作的發生率。 自2004年起，HBV患者在治療淋巴瘤時，服用抗癌藥物後所引發的高死亡率，尤其當病患血液中B型肝炎表面抗原陽性者，HBV復發率介於33-85%，並漸漸受到美國食品藥物管理局關注，而其中的抗癌藥物便是Rituximab。Rituximab為美國Genentech公司生產的單株抗體，此抗體會與病變或者正常B細胞上特有的生物標記──CD20蛋白進行結合，達到剔除B細胞目的，但並不會對不具有CD20蛋白的漿細胞造成直接影響。根據臨床上的觀察，我們假設B細胞在被清除之前，可能具有抑制HBV的功能，但目前僅限於臨床上，且對於B細胞和B型肝炎病毒之間的了解，相較T細胞更為淺薄，所以本篇論文目的，是想將此臨床現象建立至小鼠模型上，以便未來更進一步回答B細胞在宿主中，抵抗HBV所扮演的免疫角色。 於實驗結果得知，小鼠在接受藥物(clone SA271G2、Prednisone)治療後並沒有導致HBV復發。合併實驗過程B細胞的變化量，發現小鼠可能於第二劑抗體治療時已產生中和性抗體，導致B細胞剔除不完全，因此無法完全模擬臨床現象。未來可考慮使用clone 5D2抗體，代替clone SA271G2，且劑量為100微克給予小鼠，以提升B細胞清除效率、體重維持的效果，可能會得到更貼近假說的結果。

Hepatitis B is an infectious disease caused by the hepatitis B virus (HBV). More than 250 million people worldwide are still suffering from chronic hepatitis B (CHB). Hepatitis B might be linked to liver cirrhosis or hepatocellular carcinoma. According to recent clinical researches, many chronic hepatitis B patients showed high frequency of HBV reactivation after taking immunosuppressive therapy or anti-cancer drugs. Since 2004, the US Food and Drug Administration (FDA) has drawn attention to the fatal risk of hepatitis B reactivation in CHB patients after receiving immunosuppressive therapy (e.g. rituximab). Rituximab is the monoclonal antibody that targets CD20, which is a surface marker of non-malignant B cell and malignant B cell, to deplete B cell but not plasma cell. Thus, it seems that B cell has potential function to suppress HBV before rituximab treatment. Recent researches are all in clinical studies, however, we would like to establish this phenomenon on animal model and to study the role of B cell between HBV and the host. Based on our results, B cell depletion by using clone SA271G2 mAb does not lead to HBV reactivation in CBA mice with HBV persistence. Due to low efficiency of the antibody, we could not fully mimic the clinical observation. Adaptive administration of clone SA271G2 mAb repeatedly may induce neutralizing antibodies in treated mice. However, we evaluated the effect of clone 5D2 anti-mouse CD20 mAb, which showed high efficiency of B cell depletion by i.p. injecting 100μg single dosage. The antibody could more similarly mimic the clinical observation and may lead to HBV reactivation in murine model, which have HBV persistence, after or during the treatment in future.