- 學位論文
非B肝相關疾病兒童換肝後新生B型肝炎病毒感染之預後及相關危險因素
Outcome and Risk Factors of de novo HBV Infection in Pediatric Liver Transplant Recipients with Non-HBV Related Liver Diseases
摘要
非B肝相關肝病接受肝移植後才測得B肝病毒表面抗原陽性，定義為新生B型肝炎病毒感染(de novo HBV infection)的病人。對於罹患新生B型肝炎病毒感染的病人其長期追蹤後的臨床表現，我們所知有限。本研究乃探討非B肝相關肝病兒童換肝後罹患新生B型肝炎感染之發生率、危險因素、及臨床預後。 從1996到2006年間，有71位病童於臺大醫院接受B肝表面抗原陰性之活體肝臟或屍肝移植，這些病童在換肝前都不是B肝帶原者。受贈者在肝移植後會規則地檢驗肝功能、血清中免疫抑制劑藥物的濃度、並持續追蹤換肝後B肝與C肝之血清標記。肝移植前，病童的B肝疫苗接種劑數、B肝血清標記、及B肝表面抗體的效價都被紀錄，同時捐贈者的B肝血清標記亦有記載。罹患新生B型肝炎的病童，其在感染初期所保存之血清，會先以即時定量聚合鏈反應來檢測B肝病毒之病毒量與基因型，並進一步以聚合酶連鎖反應來定出B肝病毒的全部核苷酸序列；另外代表肝功能指標的丙氨酸轉氨酶(ALT)超過兩倍正常值時，會進行肝穿刺的檢查。肝臟組織學檢查的結果若排除排斥反應或其他原因造成的肝功能異常，則開始給予干安能(lamivudine)治療。 共71位研究對象中，有59位存活。分析存活病童，追蹤時間在1.2至10.2年間(中位數4.6年)。36位(61.0 %)接受來自B肝核心抗體陽性且表面抗原陰性的肝臟捐贈，有48位(81.4 %)在換肝前至少接種過3劑之B肝疫苗。換肝後得到新生B型肝炎的有9位，在換肝後的0.6到4.1年(中位數2.3年)間診斷。換肝前僅保存到49位存活者之血清，檢測其B肝表面抗體的效價，得知換肝前表面抗體大於200 mIU/ml，是預防換肝後新生B型肝炎感染之保護因子(p = 0.02)。換肝後罹患新生B型肝炎的病人，C肝抗體都是陰性，有3位換肝前為B肝核心抗體陽性，有8位接受核心抗體陽性且表面抗原陰性的肝臟捐贈。追蹤這9位換肝後新生B型肝炎感染病童的臨床表現，都沒有發生猛爆性肝炎，有5位B肝表面抗原消失，是在偵測到感染後的3到87個月之間發生；另外4位則持續帶原。共8位服用過或正服用干安能，而表面抗原消失的5位都曾接受過抗病毒藥物治療，當中的3位隨後產生B肝表面抗體，也就是55.5 %(5/9)的病人能走向B肝表面抗原消失的臨床表現，33.3 %(3/9)的病人能達到B肝表面抗原消失隨後產生表面抗體(HBsAg seroconversion)。在中位數2.3年的追蹤中，有4位持續B肝帶原，當中有2位病童，同時有B肝表面抗原與表面抗體的血清標記。僅8位成功取得B肝病毒核苷酸序列，分析後發現罹患新生B型肝炎的肝移植病童中，有75 %(6/8)的病童感染到B肝病毒a抗原決定點的突變株(“a” determinant mutants)，而沒有感染到a抗原決定點突變株的有2位，後來都從新生B型肝炎中康復(HBsAg seroconversion)。觀察感染換肝後新生B型肝炎初期所測得之病毒量與追蹤後來的臨床表現，發現走向復原(n=3)的病人，感染初期的病毒量介於 104 到 106 copies/ml之間；只有B肝表面抗原消失(n=2)的病人，感染初期的病毒量約108 copies/ml；而持續帶原者(n=4)，感染初期的病毒量介於105到109 copies/ml之間。病毒基因型方面，有7位是B型，有2位是C型。 文獻回顧中都曾探討過有幾個因素會與受贈者罹患新生B型肝炎感染有關，包括接受B肝核心抗體陽性的器官捐贈；受贈者B肝表面抗體的保護效價；移植後免疫抑制劑持續性的使用；以及可能性較低的，受贈者本身在移植前就已經是為潛藏性B型肝炎病毒感染者，卻因移植後發生B型肝炎病毒再活化。根據統計分析的結果，我們定出等待肝移植之病童經由B肝疫苗注射後，若擁有換肝前高效價的B肝表面抗體，即大於200 mIU/ml，可以預防新生B型肝炎的發生。雖然B肝表面抗體，在一定比例接受肝移植的病人身上，因為免疫抑制劑使用下，抗體效價可能會迅速地減低甚至偵測不到，但不論換肝後B肝表面抗體效價會隨著時間增加或減低，持續監測病童肝移植後，B肝血清標記及B肝表面抗體效價的變化是需要的。 無法否認的是，接受核心抗體陽性捐贈者的肝臟移植，是罹患新生B型肝炎感染之主要傳染途徑。換肝前是否具有B肝病毒表面抗體的保護效價，是影響新生B型肝炎感染發生的重要因素之ㄧ。在校正捐贈者核心抗體陽性這個變項後，換肝前B肝病毒表面抗體大於200 mIU/ml，對新生B型肝炎感染的發生仍具保護性(P=0.03)，也就是說，不論是否接受核心抗體陽性捐贈者的肝臟移植，我們都建議等待肝移植之病童在換肝前仍擁有大於200 mIU/ml的B肝表面抗體效價。 從追蹤9位罹患新生B型肝炎病童的臨床表現中，有2個訊息可以提示我們罹患新生B型肝炎的肝移植病童可以走向好的預後，分別是感染初期偵測不到a抗原決定點的突變株，也就是表面抗原突變株(HBsAg mutants)，與感染初期有低濃度的B肝病毒量。罹患新生B型肝炎感染的9位病童，有3位能走向B肝表面抗原消失隨後產生B肝表面抗體，當中的2位有B肝核苷酸序列可供分析，恰巧都無法在a抗原決定點找到胺基酸突變位點；其他6位有的僅走向表面抗原消失或有的持續帶原狀況者，則在a抗原決定點可以找到胺基酸126、127、129、142、143與 145位點上的突變。感染初期，也就是在9位罹患新生B型肝炎在偵測到B肝表面抗原陽性後平均約1.3個月時(範圍0.0~4.3個月間)，以即時定量聚合鏈反應的方法，檢測B肝病毒濃度後發現，病毒濃度低於105 copies/ml似乎只在能走向B肝表面抗原消失隨後產生表面抗體的病童中發生。感染初期低濃度的B肝病毒量與宿主達到更好預後的相關性，仍需要更多的研究來證實。 在沒有周全的預防措施下，兒童換肝後新生B型肝炎的發生率為15.3 %。換肝前B肝表面抗體效價超過200 mIU/ml，可能是足夠預防新生B型肝炎發生的保護因子。B肝表面抗原基因的a抗原決定點突變株發生在新生B型肝炎病童的機率可高達75 %，而沒感染到B肝病毒a抗原決定點的突變株，恰巧都發生在新生B型感染後能康復的病童身上。治療方面，一旦診斷為換肝後新生B型肝炎之病童，會先調降血清中免疫抑制劑的濃度，觀察並注意排斥反應發生的可能，並且在肝功能異常時考慮給予干安能抗病毒藥物的治療，治療目標設定在表面抗原消失且隨後表面抗體產生。從我們的經驗中得知，罹患換肝後新生B型肝炎的病童，有超過一半的比例，能成功地走向B肝表面抗原消失的臨床表現。
並列摘要
De novo hepatitis B virus (HBV) infection is defined as HBV surface antigen (HBsAg)-negative patients become HBsAg-positive following organ transplantation. The long-term clinical outcome of de novo HBV infection after orthotopic liver transplantation (OLT) is not understood well. We aimed to assess the incidence, risk factors, and clinical outcome and its relating factors of de novo HBV infection in pediatric liver transplant recipients. From 1996 to 2006, 71 Taiwanese children with non-HBV-related liver diseases underwent OLT at the National Taiwan University Hospital. All surviving recipients were tested regularly for liver function, serum levels of immunosuppressant, HBsAg, titers of antibodies to hepatitis B surface antigen (anti-HBs), antibodies to hepatitis B core antigen (anti-HBc), and antibodies to hepatitis C virus (anti-HCV). HBV vaccination histories and the anti-HBs titers before OLT were recorded. Children waiting for OLT received the primary universal HBV immunization during their infancy. However, there was no prophylaxis for de novo HBV infection before OLT. When patients acquired de novo HBV infection, drug levels of immunosuppressant, alanine aminotransferase (ALT), and HBV serum markers, including HBsAg, anti-HBs, anti-HBc, and hepatitis B e antigen (HBeAg) and its antibody (anti-HBe) were closely monitored. Lamivudine was administrated when ALT > 80 U/L was noticed and rejection was excluded by histology examination. Meanwhile, immunosuppressant consisted of tacrolimus or cyclosporine tapered to a minimal level without the influence of the graft survival. HBV viral load and genotype were checked by real-time PCR when HBsAg was detected. Furthermore, sequencing was performed to detect any special mutants accounting for de novo HBV infection. Fifty-nine patients (33 females and 26 males) were followed-up for a median of 4.6 years (range, 1.2-10.2 yr). Of these, 36 (61.0%) received allografts from anti-HBc-positive and HBsAg-negative donors. De novo HBV infection was found in nine (15.3%) subjects after OLT, eight of whom received allografts from HBsAg-negative and anti-HBc-positive donors. Forty-eight (81.4%) subjects received three or more doses of HBV vaccine before OLT. Pre-OLT anti-HBs titers were available for 49 recipients. In the group of de novo HBV-infected recipients (n=9), one patients had an anti-HBs antibody titer >200 mIU/ml. In the group of recipients who did not have de novo HBV infection (n=40), twenty-two patients had anti-HB antibody titers >200 mIU/ml (P=0.02). No graft loss or fulminant hepatitis occurred and all were anti-HCV-negative. Five de novo HBV infection recipients underwent HBsAg clearance and the other four were still HBsAg-positive after 2.3 years (range 2.3~2.9 years) of follow-up. Eight of the nine de novo hepatitis B patients had or have taken lamivudine and five of them underwent HBsAg seroclearance. Three of the five had HBsAg seroconversion. For the four patients with HBsAg persistence, two patients were double positive for HBsAg and anti-HBs. HBV DNA sequence was available in 8/9 patients. Seventy-five percent (6/8) of de novo HBV infection children were inoculated by surface mutants. No mutations within “a” determinant were noticed in patients recovered from de novo hepatitis B. In the median of 1.3 months (0.0~4.3 months) after diagnosis of de novo HBV infection, HBV viral loads were ranged from 104 to 106 copies/ml, 108 copies/ml, and 105 to 109 copies/ml for patients with HBsAg seroconversion (n=3), HBsAg seroclerance only (n=2), and HBsAg persistence (n=4), respectively. Seven of the nine patients were infected by genotype B and the other two patients were infected by genotype C. By statistical analysis, we defined that high titers of anti-HBs (>200 mIU/ml) before OLT prevent de novo hepatitis B infection in HBsAg-negative recipients through HBV vaccination. Anti-HBs titers may decline rapidly and become undetectable in a significant proportion of patients post-transplantation. Regardless of whether the anti-HBs titers wax and wane, regular monitoring of anti-HBs titers and HBV serum markers after OLT is essential. The major route of de novo HBV infection is through the allografts from anti-HBc-positive donors. The protective titers of anti-HBs in recipients before OLT play an important role in determining the transmission of de novo HBV to recipients. After adjustment of the variable of donors with anti-HBc, the protective titer of >200 mIU/ml anti-HBs remained significant (P=0.03). We speculated that two factors signaling a better outcome for de novo HBV infection could be the absence of HBsAg variants and lower viral loads (<105 copies/ml) in the early phases of infection. No mutations within “a” determinant were found in patients who recovered from de novo hepatitis B. In contrast to those who could not undergo HBsAg seroconversion, mutations within “a” determinant did exist at aa 126, 127, 129, 142, 143, and 145. Levels of HBV DNA seemed to be lower in patients who ran a resolving course. In conclusion, the incidence of de novo HBV infection in pediatric OLT recipients is 15.3% in the absence of adequate prophylaxis. An anti-HBs titer of >200 mIU/ml before OLT may be sufficient to prevent de novo HBV infection in HBsAg-negative recipients. The incidence of “a” determinant mutants in de novo HBV infection OLT recipients was up to 75%. Absence of HBsAg mutants might be a good prognosis factor. With the help of lamivudine, and possible decreasing the dose of calcineurin inhibitors, the outcome of de novo HBV infection might run a successful HBsAg seroclearance clinical course.