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Chinese Journal of Hepatology logoLink to Chinese Journal of Hepatology
. 2022 Apr 20;30(4):429–438. [Article in Chinese] doi: 10.3760/cma.j.cn501113-20220327-00143

抗乙型肝炎新药临床试验终点及抗病毒疗效评判指标的选择

Rational selection of virologic and immunological biomarkers and therapeutic endpoints in the clinical trials of new drugs treating chronic hepatitis B

Cooperative Group of Basic Research and Experimental Diagnosis of Liver Diseases, Chinese Society of Hepatology, Chinese Medical Association
Editor: 彭 智
PMCID: PMC12770749  PMID: 35545570

Abstract

Hepatitis B virus (HBV) infection remains to be the major cause of chronic liver diseases in China. Since the nucleos (t) ide analogues and pegylated interferon-alpha do not directly target the covalently closed circular DNA (cccDNA) in the nuclei of HBV-infected hepatocytes, those standard-of-care medications cannot efficiently cure the infected hepatocytes and rarely achieve the functional cure of chronic hepatitis B (CHB). Therefore, new antiviral drugs targeting distinct steps of HBV replication and immunotherapeutics reinvigorating antiviral immune responses are urgently needed for the functional cure of CHB. Based on the extensive discussion of the biological and clinical significance of new virologic biomarkers and distinct mechanism of drug candidates currently in clinical development, we propose that the selection of virologic and immunological biomarkers for evaluation of therapeutic efficacy as well as setting the therapeutic endpoints in the clinical trials should be based on the mode of action of investigational drugs. In addition, due to the complexity of CHB pathogenesis, selection of specific subpopulation of CHB patients for the clinical trials of drugs with a specific mode of action should also be considered.

Keywords: Chronic hepatitis B, Treatment, Antiviral drug, Clinical trial, Serological marker


世界卫生组织(World Health Organization,WHO)的最新数据显示,2019年全球共有2.96亿慢性乙型肝炎病毒(hepatitis B virus,HBV)感染者[1]。我国现有慢性HBV感染者约7 000万,慢性乙型肝炎(chronic hepatitis B,CHB)患者有2 000万到3 000万人[2]。慢性HBV感染是我国肝硬化、肝功能失代偿以及肝细胞癌(hepatocellular carcinoma,HCC)发生的最主要病因[3]。现有的两类抗病毒药物,即核苷(酸)类似物[nucleos(t)ide analogues,NAs]和聚乙二醇干扰素α(pegylated-interferon α,Peg-IFNα),可有效减缓疾病进程,减少终末期肝病的发生,但难以使患者清除血清乙型肝炎表面抗原(hepatitis B surface antigen,HBsAg),实现功能性治愈(functional cure)或临床治愈(clinical cure)[4,5]。因此,亟需研发靶向HBV生命周期不同阶段和有效促进宿主抗HBV免疫的药物,以显著提高CHB的治愈率。

肝细胞内HBV共价闭合环状DNA(covalently closed circular DNA,cccDNA)的长期存在是维持病毒慢性感染及停药后复发的主要原因[6],故cccDNA的定量检测和转录活性判定具有重要的临床意义,但因依赖于有创的肝穿刺活检,极大地限制其临床应用[7]。传统的血清病毒学标志物HBV DNA、HBsAg及乙型肝炎e抗原(hepatitis B e antigen,HBeAg)可在不同程度上反映肝组织内cccDNA的水平和转录活性,被广泛用于HBV感染状态的判断和抗HBV药物的疗效评价[8,9,10]。但随着研究的深入,上述传统血清学标志物作为药物疗效评价指标的局限性越来越凸显。

近年的研究发现,HBV前核心蛋白(precore,preC)除了产生外泌的HBeAg外,还可产生羧基端切除但氨基端19个氨基酸信号肽保留的p22Cr蛋白,并与HBeAg、乙型肝炎核心抗原(hepatitis B core antigen,HBcAg)共同构成乙型肝炎核心相关抗原(hepatitis B core-related antigen,HBcrAg),在CHB患者血液中可检测到[11]。除此之外,CHB患者血液中还存在“HBV RNA病毒样颗粒”,数量约为Dane颗粒的0.1%,其病毒核酸主要为前基因组RNA(pregenomic RNA,pgRNA)及其残存片段[12]。HBcrAg和HBV RNA均来自cccDNA,二者被认为是反映肝内cccDNA水平和转录活性的良好血清学替代标志物[13,14,15]。本文总结了传统及新型HBV血清学标志物的生物学特征和临床意义,并提出在抗HBV新药疗效评价和临床试验终点判定中,应根据药物的不同作用靶点和机制,合理选择适宜的HBV血清学标志物,以期为抗HBV新药研发及相应临床研究提供理论依据。

一、反映cccDNA转录活性的血清学标志物

肝组织内的cccDNA有从头感染(包括再感染)和新组装的核衣壳进入肝细胞核再补充两个来源[16,17]。以微小染色体形式存在的cccDNA可转录出病毒复制所需的全部RNA[18]。图1可见,3.5 kb超基因组长度的preC mRNA和pgRNA仅可转录自cccDNA。因此,preC mRNA来源的HBeAg和p22Cr[11]、pgRNA来源的HBcAg,以及总HBcrAg的定量检测在一定程度上均可反映cccDNA的转录活性[13,19,20]。血清HBcrAg已成为评价抗病毒治疗应答和预测停药后复发的重要指标[21,22,23,24,25]。血清HBV RNA也可用于评价NAs和Peg-IFNα的抗病毒疗效[14,15,26,27,28],且由于不受NAs治疗的直接影响,停药时HBV RNA低于检测下限、HBV DNA联合HBcrAg[29,30,31,32]或HBsAg消失[33]可进一步降低NAs停药后的病毒学复发率。血清HBV RNA作为HBV新型血清学标志物被写入了多项指南和专家共识[3,21,22,23,24,25,34,35],并被写入美国食品药品监督管理局(Food and Drug Administration,FDA)关于抗HBV新药申报的指导意见中[36]。但需要特别强调的是,对于直接靶向HBV RNA或抑制pgRNA包装/核衣壳装配的抗病毒药物,其血清HBV RNA的降低或消失并不能反映肝内cccDNA的清除和沉默。此外,血清HBV RNA和HBcrAg两个指标尚需更多的临床研究来确证其临床意义。其中,HBV RNA的不足之处是尚缺少国际公认的标准化HBV RNA检测试剂,且需要更多的研究来进一步描述循环HBV RNA的组成,并进一步评估其在抗病毒治疗中的应用[22]。而现有的HBcrAg试剂则存在检测下限过高、灵敏度有限的问题,尤其是对HBeAg阴性患者,未来尚需要进一步改进[37]。

图1. HBV复制周期及相应血清病毒学指标示意图.

图1

注:cccDNA:共价闭合环状DNA;cytoplasma:细胞质;Dane particle:丹氏颗粒;DSL-DNA:双链线性DNA;DSL-DNAparticle:含有双链线性DNA的病毒颗粒;Empty virion:空病毒颗粒;Endoplasmic reticulum:内质网;Filamentous particle:丝状颗粒;Golgi complex:高尔基复合体;HBcAg:乙型肝炎核心抗原;HBeAg:乙型肝炎e抗原;HBsAg:乙型肝炎表面抗原;HBx:乙型肝炎X蛋白;HSPG:硫酸乙酰肝素蛋白多糖;Immature DSL-DNA capsid:未成熟的含双链线性DNA的核衣壳;Immature pgRNA capsid:未成熟的含前基因组RNA的核衣壳;Integration:整合;MVB:多囊泡小体;Naked capsid:裸衣壳;NTCP:钠离子-牛磺胆酸共转运多肽;Nucleus:细胞核;preC:前核心蛋白;preS1:前S1基因;preS2/S:前S2/S基因;pregenomic RNA:前基因组RNA;Polymerase:聚合酶;pgRNA virion-like particle:前基因组RNA病毒样颗粒;rcDNA:松弛环状DNA;Spherical particle:球状颗粒;p22Cr:分子量为22×103的前核心蛋白。图示为完整的HBV复制周期,其中*表示HBV血清学标志物HBcrAg,由preC mRNA编码的前核心蛋白经修饰切割后形成的HBeAg、p22Cr,以及由pgRNA编码的HBcAg共同组成

由于血清HBsAg存在cccDNA和整合HBV DNA片段两个来源,其与cccDNA的相关性在长期抗病毒治疗或HBeAg自然转阴的患者中会有所下降[9,38,39,40]。但临床上无论是血清HBsAg自然消失,还是抗病毒治疗后的阴转,使包括原发性肝癌在内的HBV相关肝病的发生风险均显著降低[41]。因此,以患者血清HBsAg消失(伴或不伴抗-HBs阳转)作为的“临床治愈”血清学标志物更为医生和患者所接受。但是需要注意的是,对于那些直接靶向肝内HBV转录本或抑制HBsAg释放的抗病毒药物,血清HBsAg水平的降低及阴转并不一定代表着cccDNA的转录沉默或清除,即非真正意义上的“临床治愈”。

二、CHB抗病毒治疗临床终点的定义

功能性治愈是指在有限疗程的抗病毒治疗后,在患者血清HBV DNA持续低于检测下限、肝脏生化学指标恢复正常及HBeAg阴转或血清学转换的前提下,再确证HBsAg消失(有或无抗-HBs阳转)。我国学者基于这些患者的肝损伤恢复、肝癌发生风险和总体肝病相关死亡风险显著下降,又将之命名为“临床治愈”。“临床治愈”被认为是CHB患者抗病毒治疗的理想终点。但由于广泛存在的HBV DNA整合片段能够表达HBsAg[38,39],即使是患者肝组织内的cccDNA已被有效清除或转录沉默,其血清HBsAg仍难以阴转。2016年,美国肝病学会和欧洲肝病学会的部分专家提出了“部分治愈”(partial functional cure)的概念,并于2019年做了进一步的修订:即在有限时长的抗病毒治疗后,尽管患者的血清HBsAg仍可检测到,但已发生HBeAg阴转、肝生化学及肝功能指标恢复正常,且血清HBV DNA在治疗及停药后均持续低于检测下限[22],考虑到NAs停药仅适合于少部分患者,为使“部分治愈”在临床实践中有可操作性,有学者提出以血清HBV DNA和HBV RNA检测阴性,并结合低血清HBcrAg定量及HBsAg定量(如HBsAg<100 IU/ml)等进行综合研判[42]。但是,目前HBsAg定量仍是最可信的预测标志物。此外,我国早期临床研究报道,对“部分治愈”中血清HBsAg水平低于1 500 IU/ml的患者进行序贯Peg-IFNα治疗,可提高其“临床治愈”率[43,44]。而随后的研究则进一步提示,血清HBsAg水平更低的NAs经治患者在接受Peg-IFNα后可显著提高其“临床治愈”率[24,45]。2019年欧洲肝病学会和美国肝病学会对“功能性治愈”进行了更多层次的定义[22],在此基础上我们提出了新的CHB“阶段性治愈”定义(表1)。其中,欧美相关专业组织提出的经治后达到的“从未感染”状态,因缺乏理论和临床应用价值,未被列入。

表1. CHB的阶段性“治愈”定义及其相应特征(修改自文献[22,46]).

定义及描述 完全治愈 功能性治愈(临床治愈) 部分治愈
疾病状态 类似急性乙型肝炎康复,无肝炎活动 类似CHB血清HBsAg(自发)消失 类似停药后非活动携带者
HBsAg 低于检测下限 低于检测下限 低值阳性
抗-HBs 阳性/低于检测下限 阳性/低于检测下限 低于检测下限
血清HBV DNA 低于检测下限 低于检测下限 低于检测下限
HBeAg 低于检测下限 低于检测下限 低于检测下限
HBcrAg 低于检测下限 低于检测下限 低于检测下限或低值阳性
肝组织cccDNA 不可检出/或可检出(治愈相关OBIa)[47,48] 可检出(治愈相关OBI) 可检出
cccDNA转录活性 非活跃状态 非活跃状态 低水平选择性转录,不足以完成整个复制周期
血清HBV pgRNA 低于检测下限 低于检测下限 低于检测下限
整合HBV DNA及转录活性 或可检出无 可检出无 可检出有
停药后发生病毒学反弹或再激活b[21] 肝组织存在复制全能型HBV DNA(cccDNA、rcDNA)[49],有再激活风险 部分患者可出现血清HBsAg阳转,甚至病毒学反弹[50,51,52] 发生病毒学反弹风险较未达到部分治愈人群低
肝癌风险 显著降低,接近非感染人群 降低,随治愈时间延长而进一步降低,50岁以前HBsAg消失者发生肝癌风险更低[53] 降低[54]

注:cccDNA:共价闭合环状DNA;CHB:慢性乙型肝炎;HBcrAg:乙型肝炎核心抗原相关抗原;HBsAg:乙型肝炎表面抗原;HBV:乙型肝炎病毒;HBV pgRNA:HBV前基因组RNA;抗-HBs:乙型肝炎表面抗体;OBI:隐匿性HBV感染;rcDNA:松弛环状DNA;a:治愈相关OBI:排除窗口期感染,按照现有检测技术,血清HBsAg阴性,但肝组织中HBV rcDNA或cccDNA阳性,对应血清HBV DNA低于检测下限或低值阳性(<200 IU/ml);b:HBV再激活:HBsAg阳性/抗-HBc阳性,或HBsAg阴性/抗-HBc阳性患者接受免疫抑制治疗时,HBV DNA较基线升高≥2 log10IU/ml,或基线HBV DNA阴性转为阳性,或HBsAg由阴性转为阳性

三、血清学标志物在抗乙型肝炎新药疗效评价和临床试验终点判定中的应用

目前,处于临床研究阶段的靶向HBV复制不同关键环节的直接抗病毒药物(direct-acting antiviral agent,DAA)包括:新的NAs、核心蛋白变构调节剂(core protein allosteric modulators,CpAMs)、进入抑制剂(entry inhibitor)、以核酸聚合物(nucleic acid polymers,NAPs)为代表的HBsAg释放抑制剂、siRNA或反义寡核苷酸(antisense oligodeoxynucleotides,ASOs),以及靶向cccDNA的基因编辑和靶向HBV的治疗性抗体等。而在研免疫调节剂类药物主要通过激活人体固有免疫或HBV特异性的免疫应答来发挥抗病毒作用,包括天然免疫激动剂、治疗性疫苗、免疫检查点抑制剂等(表2)。在抗HBV新药临床研究的疗效评价和临床试验终点判定中,应根据药物的不同作用靶点和机制,选择最适宜的血清病毒学标志物,以准确反映肝组织内cccDNA的水平和转录活性。

表2. 已进入临床试验阶段的抗HBV在研新药疗效评价及临床试验终点评判的标志物建议.

药物类别 作用机制 疗效评价及临床试验终点的适宜血清标志物 参考文献
1.直接抗病毒药物 靶向病毒复制的各个环节
核苷(酸)类药物 通过竞争性抑制P蛋白逆转录活性阻止rcDNA合成 血清HBV DNA低于检测下限a。巩固治疗后部分患者可实现“部分治愈”,以血清HBV DNA、HBV RNA双阴性及HBsAg、HBcrAg低值阳性作为组合指标,可提高停药安全性 [14,22,58,59]
进入抑制剂 干扰HBV进入肝细胞 血清HBV DNA、HBV RNA和HBsAg显著下降 [61]
核心蛋白变构调节剂b 干扰或破坏HBV衣壳的形成 血清HBV DNA、HBV RNA及HBcrAg显著下降或低于检测下限。血清HBV DNA、HBV RNA双阴性,HBsAg消失或大幅下降至较低值(如<100 IU/ml),可提高停药安全性 [66,68,71,72]
siRNA,ASO 降解HBV RNA HBsAg、HBV DNA及HBV RNA显著下降或低于检测下限 [73,74,75]
核酸聚合物类药物 干扰HBsAg的释放 HBsAg显著下降或低于检测下限。HBsAg消失且血清HBV DNA、HBV RNA均低于检测下限,可提高停药安全性 [78,79]
HBV靶向治疗性抗体 诱导HBsAg免疫清除,或阻断病毒感染新生肝细胞 HBV DNA、HBsAg显著下降或低于检测下限。HBsAg消失及血清HBV DNA、HBV RNA均低于检测下限,可显著提高停药安全性 [82,83,84,85]
2.免疫调节剂 激活免疫功能抑制HBV复制或清除HBV感染细胞
干扰素 抑制cccDNA转录,促进抗病毒免疫功能 HBsAg显著下降或低于检测下限;抗-HBs出现或显著升高,HBV特异性的T和B细胞亚群数量增加,增殖能力增强,表型由耗竭PD-1、TIM3和LAG3高表达转为激活(IFN-γ和IL-2产生) [90,91]
治疗性疫苗c 用疫苗诱导HBV特异性T和B细胞应答,降低循环抗原水平和HBV感染的肝细胞数 [92,93]
天然免疫激动剂d 激活天然免疫系统,并具有激活HBV特异性B细胞或T细胞的能力 [94,95]
免疫检测点抑制剂 PD-L1抑制剂,改善HBV特异性T和B细胞应答 [96]

注:ASO:反义寡核苷酸;cccDNA:共价闭合环状DNA;HBV:乙型肝炎病毒;HBsAg:乙型肝炎表面抗原;HBcrAg:乙型肝炎核心抗原相关抗原;IFN-γ:干扰素γ;IL-2:白细胞介素-2;LAG3:淋巴细胞活化基因3;抗-HBs:乙型肝炎表面抗体;PD-1:程序性细胞死亡受体1;PD-L1:程序性细胞死亡受体配体1;rcDNA:松弛环状DNA;siRNA:干扰RNA;TIM3:T淋巴细胞免疫球蛋白黏蛋白3;a:HBeAg阳性患者可将其阴转或血清学转换用于疗效的阶段性评价;b:I型和II型变构剂因作用机制存在差异,其评价指标可能不同;c:抗原特异性的抗体水平升高;d:血清中促进病毒清除的细胞因子IFN-α、TNF-α、IL-6、IL-8 和 IL-12水平升高[55]

1.直接抗病毒药物:(1)NAs:由于现有一线NAs类药物对HBV DNA复制的强效抑制作用[56],NAs仍是许多在研新药联合治疗时的基础用药。但近20%的低病毒血症发生率提示我们,仍有必要研发更强效的新型NAs[57]。接受NAs治疗的患者HBV DNA阴转后,随着cccDNA池的不断耗竭,患者血清HBV RNA、HBcrAg也会随之减少,故其血清HBV RNA和HBcrAg水平可以反映肝组织内cccDNA状态[58,59]。患者按HBV RNA、HBcrAg顺序依次发生阴转(或低于检测下限)[59]。

(2)进入抑制剂:进入抑制剂布列韦肽(bulevirtide,BLV)为肉豆蔻酰化多肽,带有L-HBsAg的PreS1区序列,能够结合NTCP以阻止HBV和丁型肝炎病毒(hepatitis D virus,HDV)进入细胞。在HBV和HDV共感染患者中开展的临床试验结果显示,BLV单药或联合Peg-IFNα治疗对于降低HDV RNA均有较好的疗效,但HBsAg下降幅度很小[60]。目前BLV与ETV联用治疗CHB的临床研究正在进行中,其疗效尚不确定[61]。

(3)核心蛋白变构调节剂:CpAMs按其作用机制可分为导致衣壳结构形态异常的Ⅰ型CpAMs和促进形态“正常”但具有空衣壳结构(无pgRNA包裹)的Ⅱ型CpAMs[62,63]。1998年,Prevelige[62]建议通过CpAMs来治疗CHB。Ⅰ型和Ⅱ型CpAMs皆可特异性结合于衣壳蛋白二聚体间的疏水性口袋,干扰pgRNA的包装并抑制其逆转录形成HBV DNA[64,65],此时血清HBV DNA和HBV RNA水平均不能真实反映肝组织内cccDNA的转录活性。但对于Ⅱ型CpAMs,由于其诱导形成的空衣壳仍可释放入血[66],血清HBcrAg水平或许能较好反映cccDNA的转录活性。而Ⅰ类CpAMs可引起非衣壳样的多聚体形成并最终在胞内被降解[67],血清HBcrAg是否还能准确反映Ⅰ类CpAMs治疗下肝内cccDNA的转录活性尚存疑问。另外,也有报道CpAMs可诱导成熟核衣壳变构或错误解聚[68],导致rcDNA无法被精准递送至肝细胞核内合成cccDNA,或直接降低HBeAg分泌[69,70]。所以,我们建议以血清HBV DNA、HBV RNA降低作为药效评价标志物[66,68],联合HBcrAg和HBsAg定量检测或可提高停药后病毒学应答的维持[71,72],但这需要高质量临床研究进一步验证。

(4)靶向病毒RNA的药物:靶向HBV RNA特定位置的小干扰RNA(short interfering RNAs,siRNAs)和ASOs可以减少包括pgRNA在内的、转录自cccDNA或整合HBV DNA片段的所有HBV病毒转录本,抑制病毒蛋白的翻译,发挥抗HBV作用。目前已有靶向HBV基因组相对保守的X区与S区的siRNA药物(ALH-HBV02、JNJ3989、DCR-HBVS、VIR-2218、BRⅡ-835及AB-729)和ASOs药物(Bepirovirsen,也称ISIS 505358或GSK 3228836)进入临床研究。由于并不作用于cccDNA,尽管该类药物可以降低包括血清HBsAg在内的所有病毒学指标,但这些指标的降低并不一定代表cccDNA的清除或转录沉默[73,74,75]。

(5)核酸聚合物(NAPs)类药物:有研究显示,以HBsAg为主构成的HBV亚病毒颗粒(subviral particle,SVP)的组装起始于内质网(endocytoplasmic reticulum,ER)膜,ER膜上的HBsAg可通过囊泡萌芽进入内质网高尔基体中间隔室(ER/ERGIC)的管腔,并由此释放到胞外[76,77]。NAPs的化学本质为硫代寡核苷酸,能够抑制SVP的组装和分泌,阻断HBsAg释放[78]。目前该类药物已进入III期临床研究的有REP 2139和REP 2165两种。由于NAPs的作用只是干扰HBsAg释放,对HBV复制的其他环节无明显抑制作用[78,79],故NAPs单药治疗引起的血清HBsAg消失并不是真正意义上的“临床治愈”,应综合监测血清HBV DNA、HBV RNA、HBeAg以及HBcrAg水平的动态变化以评价其抗病毒疗效。

(6)靶向cccDNA的CRISPR/Cas9基因编辑:理论上,CRISPR/Cas9基因编辑系统可以直接靶向并清除cccDNA,特别是双gRNA介导的CRISPR/Cas9系统可造成cccDNA的大片段缺失,显著降低HBsAg及HBeAg水平[80]。基于该系统的碱基编辑工具还可以在不造成宿主双链断裂的前提下,在HBV基因组中引入无义突变,抑制HBV复制[81]。目前,美国Excision Biotherapeutics公司的EBT-107正处于临床前研究阶段。鉴于基因编辑药物的作用靶点为cccDNA,理论上,血清HBV DNA、HBV RNA水平以及血清病毒抗原HBsAg、HBeAg和HBcrAg水平均会降低,都可以作为评价抗病毒疗效的标志物[9,13,14,20]。

(7)HBV靶向治疗性抗体:此类抗体是近年来发展最为迅速的靶向药物类型之一,其可特异性结合体内HBsAg并通过抗体Fc片段介导的调理作用实现HBsAg的高效清除,有望通过多剂次给药或联合其他类型的抗HBV药物实现对HBsAg的持久抑制,进而促进机体建立针对HBV的特异性应答,以提高临床治愈率。目前已有数个候选单克隆抗体在临床前研究和早期临床试验中表现出一定的临床应用潜力[82,83,84,85]。其中Lenvervimab是重组人IgG1,在CHB患者中开展的Ⅰ期临床试验中发现,单针次给药组所有患者的HBsAg水平均在给药24 h后降至最低(0.03~2.86 IU/ml),但随即反弹,因此仍需探索更合适的给药程序和治疗方案[86]。VIR-3434是全人源单克隆抗体,健康受试者对高达3 000 mg的单剂量VIR-3434表现出良好的耐受性;对6例乙型肝炎患者的检测结果显示,给予6 mg的VIR-3434治疗,可使患者的HBsAg滴度平均降低1.3 log10IU/ml,提示该抗体具备较好的开发潜力[85]。综合抗体类药物的临床前研究和临床试验初步结果,建议考虑HBsAg、HBV DNA显著下降或低于检测下限作为评价抗体疗效的标志物[82,83,84,85]。

2.免疫调节剂及其他药物:目前已进入临床研究的免疫调节剂主要有天然免疫调节剂、治疗性疫苗以及免疫检查点抑制剂等[87]。其中天然免疫调节剂如Toll样受体7(Toll-like receptor,TLR7)激动剂Vesatolimod(GS-9620)、TLR8激动剂Selgantolimod(GS-9688)在动物实验中均显示出显著的抗病毒效果。程序性细胞死亡配体1(programmed cell death-ligand 1,PD-L1)抑制剂ASC 222也已进入Ⅱ期临床研究。治疗性疫苗主要包括重组HBsAg蛋白疫苗、基于T淋巴细胞表位的脂肽疫苗、DNA疫苗、酵母源疫苗和腺病毒载体疫苗等,其中基于HBsAg和HBcAg重组蛋白的治疗性疫苗NASVAC已进入Ⅲ期临床研究[88],针对Pre-S1、Pre-S2和S的治疗性疫苗BRII-179/VBI-2601进入Ⅱ期临床研究[89]。

免疫调节剂主要通过激活宿主免疫来杀伤感染HBV的肝细胞、直接清除或抑制HBV cccDNA活性来发挥抗病毒作用,故血清HBV DNA、HBV RNA、HBsAg、HBeAg和HBcrAg均可作为肝组织HBV cccDNA的替代标志物,用于该类药物的疗效评判。此外,由于免疫调节剂很可能会显著增加HBV特异性T细胞和B细胞反应,其疗效评价也需检测反映宿主免疫功能的免疫细胞和炎症因子。这些免疫细胞在清除病毒感染时往往会带来肝细胞的损伤,因此也需要密切关注血清丙氨酸转氨酶、天冬氨酸转氨酶或高尔基体蛋白73水平的变化,其明显升高或可作为间接反映CHB患者免疫激活的标志[90,91,92,93,94,95,96]。

此外,也有通过影响宿主肝细胞功能来抑制HBV复制的研发药物,如法尼酯X受体(farnesoid X receptor,FXR)激动剂[97]和诱导HBV RNA降解的非经典多聚腺苷酸聚合酶相关结构域5/7 [non-canonical poly(A)RNA polymerase domain 5/7,PAPD5/7]抑制剂(RG-7834)等[98],在未来研发及后续临床试验时需注意这些药物对于宿主功能的潜在影响[99]。

四、展望

鉴于现有两类抗病毒药物NAs和Peg-IFNα的临床治愈效果存在明显的瓶颈,亟需研发新的抗HBV药物以获取更好的疗效。截至目前,已有多款直接靶向HBV复制周期的抗病毒药物进入临床前及临床试验阶段。需要谨记的是,我们可能不宜以单一的血清HBsAg水平显著下降或消失作为临床治愈的标志物来评价DAA的临床疗效,以免使一些能显著抑制cccDNA池维持、但未必能快速促使HBsAg水平下降的潜在抗HBV药物失去发展机会。因此,在进行药物疗效评价时,除动态监测血清病毒学标志物的动态变化外,肝穿刺活检测定肝组织内cccDNA水平的变化具有重要意义,但是该检测在临床试验中的可行性还需要进一步探讨[7,100]。

另一方面,越来越多的研究提示,HBsAg对宿主免疫细胞功能具有广泛的抑制作用[101],因此在未来的抗病毒临床实践中,或可考虑NAs、NAPs或siRNA联用Peg-IFNα或其他免疫调节剂,在降低HBsAg水平解除CHB患者的免疫抑制状态的同时,加速感染肝细胞和表达整合来源HBsAg的肝细胞清除,以提高CHB患者的临床治愈率。事实上,目前已有多种DAA新药的Ⅱ期临床试验采用了与免疫激活剂联用的策略。对于此类不同药物联用的临床试验,未来还需要通过更多的临床研究加以观察、评估和论证,以确定最适的病毒学和免疫学评价指标,使临床试验的经济社会效益最大化。除此之外,CHB疾病进程复杂,不同的在研药物因其作用机制不同,可能有其最适宜的、能最大获益的患者亚群,在临床试验中也应予以考虑。

编写组成员(按姓氏拼音排序):

陈红松 北京大学人民医院肝病研究所

陈香梅 北京大学基础医学院病原生物学系暨感染病中心

高志良 中山大学附属第三医院感染性疾病科

郭巨涛 美国巴鲁克布隆伯格研究所

胡鹏 重庆医科大学附属第二医院感染与肝病中心

黄鸿鑫 北京大学基础医学院病原生物学系暨感染病中心

黄爱龙 重庆医科大学感染性疾病分子生物学教育部重点实验室

鲁凤民 北京大学基础医学院病原生物学系暨感染病中心北京大学人民医院肝病研究所

欧启水 福建医科大学附属第一医院

任红 重庆医科大学附属第二医院感染与肝病中心

孙剑 南方医科大学南方医院

王福生 解放军总医院第五医学中心感染病医学部 国家感染性病疾病临床医学研究中心

王雷婕 北京大学基础医学院病原生物学系暨感染病中心

夏宁邵 厦门大学公共卫生学院国家传染病诊断试剂与疫苗工程技术研究中心 国家药监局传染性疾病检测技术研究与评价重点实验室

于乐成 解放军东部战区总医院感染科与肝病中心

庄辉 北京大学基础医学院病原生物学系暨感染病中心

志谢

图1中的素材均来源于BioRender.com,并由BioRender.com修改制作完成(https://app.biorender.com/biorender-templates)。本文初稿征询了多位药企乙型肝炎新药研发从业人员的意见并得到积极反馈,一并志谢

引用本文:

中华医学会肝病学分会肝病基础医学与实验诊断协作组. 抗乙型肝炎新药临床试验终点及抗病毒疗效评判指标的选择[J].中华肝脏病杂志,2022,30(4):429-438. DOI:10.3760/cma.j. cn501113-20220327-00143.

利益冲突:

所有作者均声明不存在利益冲突

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