乙型肝炎病毒相关的肝细胞癌(HBV-HCC)通常被认为是与暴露于HBV和肿瘤抗原引发的慢性炎症相关的炎症相关的癌症。目前主要的治疗方案包括肝切除、肝移植、局部消融以及索拉菲尼化疗等方案。免疫治疗是一种新的治疗策略,通过增强机体自然免疫反应来治疗HBV-HCC,目前针对PD-1或CTLA-4的检查点阻断疗法已经在HCC患者中显示出初步的疗效。由于CD8+细胞毒性T淋巴细胞(CTLs)的产生在抗肿瘤免疫反应中起着重要作用,所以进一步探索HBV相关肝癌的CD8+T细胞抗肿瘤免疫机制非常必要。由于HBV相关肝癌的CD8+T细胞对HCC的免疫反应主要由病毒载量、肿瘤的抗原性以及癌症组织的微环境之间的平衡决定,本文将从HBV病毒载量、肿瘤抗原性以及肿瘤微环境三方面进行综述。
Hepatitis B virus-associated hepatocellular carcinoma (HBV-HCC) is generally considered to be associated with chronic inflammation associated with exposure to HBV and tumor antigens. At present, the main treatment options include hepatectomy, liver transplantation, local ablation and sorafinib chemotherapy. Immunotherapy is a new treatment strategy to treat HBV-HCC, by enhancing the body’s natural immune response. At present, checkpoint blocking therapy for PD-1 or CTLA-4 has shown a preliminary effect in patients with HCC. Since the production of CD8+ cytotoxic T lymphocyte (CTLs) plays an important role in anti-tumor immune response, it is necessary to further explore the anti-tumor immune mechanism of CD8+T cells in HBV-related hepatocellular carcinoma. Since the immune response of CD8+T cells of HBV-related hepatocellular carcinoma to HCC is mainly determined by the balance among viral load, tumor antigenicity and cancer tissue microenvironment, this article will review the HBV viral load, tumor antigenicity and tumor microenvironment.
乙型肝炎病毒,肝细胞癌,CD8+T细胞, Hepatitis B Virus Hepatocellular Carcinoma CD8+T Cell摘要
Research Progress on Anti-Tumor Immune Mechanism of CD8+T Cells in HBV-Related Hepatocellular Carcinoma
Dandan Ren*, Jinxin Ma#
Affiliated Hospital of Yan’an University, Yan’an Shaanxi
Received: Apr. 25th, 2021; accepted: May 8th, 2021; published: May 27th, 2021
ABSTRACT
Hepatitis B virus-associated hepatocellular carcinoma (HBV-HCC) is generally considered to be associated with chronic inflammation associated with exposure to HBV and tumor antigens. At present, the main treatment options include hepatectomy, liver transplantation, local ablation and sorafinib chemotherapy. Immunotherapy is a new treatment strategy to treat HBV-HCC, by enhancing the body’s natural immune response. At present, checkpoint blocking therapy for PD-1 or CTLA-4 has shown a preliminary effect in patients with HCC. Since the production of CD8+ cytotoxic T lymphocyte (CTLs) plays an important role in anti-tumor immune response, it is necessary to further explore the anti-tumor immune mechanism of CD8+T cells in HBV-related hepatocellular carcinoma. Since the immune response of CD8+T cells of HBV-related hepatocellular carcinoma to HCC is mainly determined by the balance among viral load, tumor antigenicity and cancer tissue microenvironment, this article will review the HBV viral load, tumor antigenicity and tumor microenvironment.
Keywords:Hepatitis B Virus, Hepatocellular Carcinoma, CD8+T Cell
HBV DNA即是乙肝病毒的脱氧核糖核酸(即乙肝病毒基因)。HBV-DNA是HBV感染最直接、特异性强和灵敏性高的指标,HBV-DNA阳性,提示HBV复制和有传染性。HBV-DNA越高表示病毒复制越厉害,传染性强。在HBV急性感染期间,一般会在感染几周后可以检测到多特异性的、多功能的乙肝病毒特异性T细胞,然而,在慢性乙型肝炎(CHB)患者和HBV-HCC患者中,HBV特异性CD8(+)T细胞频率的检测率非常低 [5]。这可能是因为CHB患者和HBV-HCC患者中通常表现为无效的CD8+T细胞反应。CD8+T细胞失效的一个原因是病毒序列突变的出现,这可能导致抗病毒CD8+T细胞失去识别能力从而没有被APC充分激活。另一个关键决定因素是一种称为T细胞衰竭的现象,即病毒特异性CD8+T细胞抗病毒效应功能逐渐丧失,包括细胞因子产生减少、细胞毒性降低和增殖能力受损 [6]。Li Z [7] 等对8例未经治疗的HCC患者肿瘤浸润的CD8+T细胞和从其他组织来源(瘤周组织)分离的CD8+T细胞进行了外显子组和转录组全序列测定。肿瘤浸润的CD8+T细胞在个体间也表现出较大的转录异质性,这受HBVDNA水平、术前抗病毒治疗和T细胞浸润程度等临床特征的调节。HBV病毒载量可能在某种程度上反映了抗肿瘤免疫活性,因为HBV水平低的患者往往表现出更高的T细胞增殖信号的表达。Witjes等 [8] 研究了肝癌患者HBV DNA水平是否影响患者的生存,对高病毒载量(HBV DNA > 105拷贝/ml)和低病毒载量(HBV DNA < 105拷贝/ml)的肝癌患者的生存率进行评估,发现病毒载量高的肝癌患者1年和5年生存率分别为58%和11%,病毒载量低的肝癌患者的1年和5年生存率分别为70%和35%。即HBV DNA水平与HCC患者的总体生存率相关。Huang S [9] 等在探讨抗病毒治疗(AVT)对复发性乙型肝炎病毒(HBV)相关性肝细胞癌(HCC)患者再次肝切除术后近期和远期疗效的影响的研究中纳入583名因初次肝切除术后HBV相关性肝癌肝内复发而接受再次肝切除术的患者,发现术前抗病毒治疗降低了病毒复发率,再次肝切除前后启动AVT有助于HBV相关复发HCC再次肝切除后更好的远期预后。上述研究表明血清HBV病毒载量可用于患者的免疫反应评估,在肝切除治疗中联合抗病毒药物治疗可能有利于HBV相关HCC患者的T细胞激活。总体而言,HBV病毒载量和抗病毒治疗可能会影响HCC的T细胞功能状态,进一步的大样本研究可能是有价值的。
3. 肿瘤抗原性
目前报道的最多的针对HBV相关肝癌的抗原靶点包括病毒抗原、肿瘤相关抗原(TAA)、新抗原和细菌相关性抗原。HBV整合到宿主基因组中,肝细胞癌患者的肿瘤细胞表达的HBV蛋白在患者体内可引发高亲和力的T细胞反应。TAAs是来源于内源性野生型蛋白质的表位,其在肿瘤中的表达增加,在健康组织中的数量或空间表达受到限制 [10]。目前针对HBV相关肝癌的病毒抗原和肿瘤相关抗原的免疫优势和功能仍然不太清楚。Gehring A [11] 等用酶联免疫吸附斑点技术(ELISPOT)对10例肝细胞癌、10例乙肝肝硬变、10例乙肝但无肝硬变的细胞扩增后进行分析发现,大多数肝癌患者(总共7/10)确实有可检测到的TAA特异性T细胞,其中肿瘤抗原NY-ESO-1和SSX-2是最常见的靶点,然而却很少检测到乙肝病毒特异性反应。Inada Y等 [12] 分析了32例乙型肝炎病毒(HBV)相关性肝癌、42例丙型肝炎病毒相关性肝癌和18例非酒精性脂肪性肝炎(NASH)相关性肝癌患者的临床资料。发现HBV、丙型肝炎和NASH相关的HCC群体对TAAs的免疫应答不同。具体而言,对p53和MRP3的免疫反应为在与HBV相关的HCC组中观察到高频率,对甲胎蛋白的反应为在丙型肝炎病毒相关的HCC组中观察到高频率。在NASH相关的HCC组中,只有6例(33.3%)检测到对至少一种TAA病毒的免疫应答这一频率低于HBV相关的HCC组(22/32, 68.8%)和丙型肝炎相关的HCC组(32/42, 76.2%),这表明NASH相关的HCC免疫原性低。上述研究表明HBV特异性CD8+T细胞虽然能控制肿瘤的生长,但是由于病毒慢性感染的原因,乙肝病毒特异性T细胞被耗尽或缺失,所以失去控制肿瘤生长的能力。TAA特异性CD8+T细胞虽然耗竭的程度相对较轻,但是肿瘤相关抗原的TCR亲和力较低,再加上TAA表达较少,所以可能限制了其控制肿瘤的能力。目前正在进行的针对HBV抗原和肿瘤相关抗原的过继T细胞免疫疗法,即通过引入嵌合抗原受体或已知特异性的TCR来重新定向患者血液中T细胞的特异性,可能可以解决HBV相关肝癌患者病毒特异性T细胞耗竭以及TAA亲和力低的问题。除了病毒抗原和肿瘤抗原外,新抗原也渐渐得到关注,即通过对肿瘤进行广泛的遗传和免疫学表征,以发现免疫原性HCC特异性新抗原。这些自身抗原随着特定肿瘤的发展而变异,使它们在免疫学上不同于自然产生的变异,因此更具肿瘤特异性。但是发现特定新抗原的过程非常复杂,涉及基因测序,然后是新抗原免疫原性的计算预测或广泛的实验验证,再加上新抗原的个人化性质,即突变主要是患者特有的,将这种方法转化到临床上是很繁琐的。Yang H [13] 等发现携带TP53新抗原的HCC患者总生存期比其他患者长(p = 0.0371),他们表现出更高的免疫评分(p = 0.0441),更高的细胞毒性淋巴细胞浸润(p = 0.0428),即TP53新抗原可能成为肝癌免疫治疗的潜在靶点。肝脏是受影响的主要器官,通过肝门静脉血从肠道接收食物营养和微生物代谢物,因此是微生物抗原和T细胞反应相互作用的潜在场所。Rong Y [14] 等检测了HBV相关HCC患者的细菌反应性CD8+ T细胞反应,发现来自HBV相关HCC患者的循环CD8+ T细胞表现出显著升高的细菌反应性,观察到CD8+ T细胞与Foxp3+调节性T细胞的比例与长双歧杆菌反应性和肠球菌反应性CD8+ T细胞的比例呈正相关,而PD-1+ CD8+ T细胞的频率与肠球菌反应性CD8+ T细胞的频率呈负相关。此外,HCC患者肿瘤切除后的无病生存期与双歧杆菌的出现频率呈正相关。目前尚不清楚细菌反应性CD8+ T细胞是否能通过直接消除肿瘤细胞或支持抗肿瘤免疫的其他分支积极发挥抗肿瘤功能,相关报道较少,所以还需要在控制良好的动物模型中进行进一步的研究。
任丹丹,马金鑫. HBV相关肝癌的CD8+T细胞抗肿瘤免疫机制研究进展Research Progress on Anti-Tumor Immune Mechanism of CD8+T Cells in HBV-Related Hepatocellular Carcinoma[J]. 临床医学进展, 2021, 11(05): 2347-2354. https://doi.org/10.12677/ACM.2021.115338
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