IL-12增强HBV融合抗原DNA疫苗在小鼠诱导的细胞免疫应答

乙型肝炎病毒(hepatitis B virus,HBV)极易形成慢性感染,主要机制在于感染者不能产生强有力的细胞免疫应答以清除病毒[1].慢性HBV感染者体内虽然存在HBV抗原特异性T淋巴细胞,但对HBV抗原的反应性较低.研究发现,增强这类T淋巴细胞的反应性,可以促进HBV的清除[2].     

HBV包膜-核心蛋白融合基因DNA疫苗诱导小鼠持久的细胞免疫应答

构建编码HBV包膜-核心蛋白融合基因的DNA疫苗pSC、pSS1S2C和编码HBV包膜蛋白或核心蛋白基因的DNA疫苗pHBs、pHBc,分别肌肉注射免疫BALB/c小鼠,检测小鼠的血清抗体、T细胞增殖和细胞毒性T淋巴细胞反应,比较融合基因DNA疫苗与单基因DNA疫苗诱生免疫应答的强度,发现融合基因DNA疫苗诱生抗体的效率明显不及单基因DNA疫苗,但其能诱导更强、更持久的细胞免疫应答,表明HBV包膜-核心蛋白融合基因DNA疫苗对于治疗慢性乙型肝炎可能比单基因DNA疫苗更为有效.     

A case of hepatitis B reactivation due to the hepatitis B virus escape mutant in a patient undergoing chemotherapy

A 62-year-old man had chronic hepatitis B virus (HBV) infection and was diagnosed with liver cirrhosis. At the time of diagnosis the patient’s virologic markers were positive for hepatitis B surface antigen (HBsAg), antibody to hepatitis B e antigen (anti-HBe) and antibody to hepatitis B core antigen (anti-HBc), while antibody to hepatitis B surface antigen (anti-HBs) and HBV DNA were negative. Later the patient received chemotherapy for malignancy. However, this was interrupted due to elevated liver enzymes. At the same time HBV DNA became positive. Lamivudine (LMV) therapy was administered immediately. However, the levels of serum aminotransferase and total bilirubin (TB) were still rising. Finally the patient died of fulminant hepatic failure. A sequence revealed HBV genotype C (HBsAg subtype adw) with immune escape mutations, F8L, S34L, F41S, G44V, F93C, V96G, L110I, C149Y and F161Y. The high morbidity and mortality of this complication is one of the major obstacles to completing the standard treatment for malignancy in HBV carriers. Therefore, the relative risk of antiviral prophylactic failure should be further assessed and the optimal strategy for antiviral prophylaxis in HBsAg-positive patients with oncologic and hematologic malignancies undergoing chemotherapy should be revised.     

Protective effect of hepatitis B vaccine combined with two-dose hepatitis B immunoglobulin on infants born to HBsAg-positive mothers

Background

Despite the use of hepatitis B (HB) vaccine and hepatitis B immunoglobulin (HBIG), a portion of infants are still non- or low-responders, or even immunoprophylaxis failure. We aimed to determine the immune response in the infants from the mothers being positive for hepatitis B surface antigen (HBsAg), by which the infants received three doses of HB vaccine in combination with two-dose 200 IU HBIG injections.

Methods

In this retrospective study, 621 infants from HBsAg-positive mothers in Beijing YouAn Hospital between January 2008 and December 2009 were included. All the infants were given three doses of 10 µg HB vaccine (at 0, 1 and 6 months of age) and two-dose of 200 IU HBIG (at birth and in 2 weeks of age). Serum HBsAg and antibody to HBsAg (anti-HBs) in all the infants were determined at 7 months of age.

Results

Of the 621 infants, 2.9% were immunoprophylaxis failure (positive for HBsAg), 1.4% were non-responders (anti-HBs undetectable), 95.7% were responders. The 594 responders could be categorized into three subsets, 22 were 10 to 99 IU/L for anti-HBs levels, 191 were 100 to 999 IU/L, and 381 were ≥1000 IU/L. The immunoprophylaxis failure rate was at 0% and 5.2% for the infants of HBeAg-negative and HBeAg-positive mothers(P<0.001). Infants from mothers with detectable HBV DNA had higher incidence of immunoprophylaxis failure than those of mothers without detectable HBV DNA (P = 0.002). The factors including gender, birth weight, gestation weeks, the rates of maternal HBeAg-positive, and detectable HBV DNA did not contribute to the no response to HB vaccination.

Conclusions

Through vaccination by three doses of HB and two-dose of HBIG, majority of the infants (95.7%) achieved a protective level of anti-HBs at 7 months of age. Maternal HBeAg-positive and HBV DNA detectable were associated with the immunoprophylaxis failure, but not contribute to the non- or low-response to HB vaccination.     

抗乙型肝炎病毒单克隆抗体药物的临床前药效学评价

由乙型肝炎病毒（HBV）感染导致的病毒性肝炎是世界范围内的一个重大公共卫生问题,抗HBV抗体药物乙型肝炎免疫球蛋白（HBIG）是阻断乙型肝炎母婴传播和移植性感染的主要用药。但HBIG本身存在一些问题,而重组抗HBV单克隆抗体能成为其有效替代物。在重组抗HBV抗体技术相对成熟的情况下,重组抗HBV单克隆抗体药物功能性评价体系的缺失成为阻碍抗HBV单克隆抗体药物研发的重要因素。本文就现有的抗HBV单克隆抗体药物的评价方法和体系进行综述。     

Hepatitis B virus surface antigen can activate human monocyte-derived dendritic cells by nuclear factor kappa B and p38 mitogen-activated protein kinase mediated signaling

Hepatitis B virus Ag (HBsAg), a major antigen of hepatitis B virus (HBV), is also a vaccine component for prevention of HBV infection. Dendritic cells (DCs) of HBV carriers reportedly exhibit functional impairment. In this study, the aim was to investigate the effect of HBsAg on activation of human monocyte-derived dendritic cells (MD-DCs), and the subsequent signal transduction pathway. Treatment of MD-DCs with HBsAg resulted in enhanced cell surface expression of cluster of differentiation 80, CD83, CD86 and major histocompatibility complex class II, and increased interleukin (IL)-12 p40, IL-12p70, and IL-10 production. Furthermore, HBsAg treatment of MD-DCs with HBsAg resulted in enhanced T cell-stimulatory capacity and increased T cell secretion of interferon and IL-10. The pathway of MD-DCs activation by HBsAg was further investigated in the present study. Inhibition of nuclear factor (NF)-kappa B (κB) by helenalin and p38 mitogen-activated protein kinase (MAPK) by SB203580 prevented production of IL-12 p40, IL-12 p70, and IL-10. HBsAg also augmented MAPK phosphorylation. Thus, cytokine secretion of human MD-DCs by HBsAg is blocked by inhibition of the NF-κB and p38 MAPK pathways. Likewise, decreased inhibition of kappa B alpha concentrations and MAPK phosphorylation are critical for MD-DC maturation by HBsAg. These findings may provide a strategy for improving the prophylactic and therapeutic efficacy of vaccines and tumor therapies that utilize these pathways.     

Vaccine- and hepatitis B immune globulin-induced escape mutations of hepatitis B virus surface antigen

Hepatitis B virus surface antigen (HBsAg) vaccination has been shown to be effective in preventing hepatitis B virus (HBV) infection. The protection is based on the induction of anti-HBs antibodies against a major cluster of antigenic epitopes of HBsAg, defined as the 'a' determinant region of small HBsAg. Prophylaxis of recurrent HBV infection in patients who have undergone liver transplantation for hepatitis B-related end-stage liver disease is achieved by the administration of hepatitis B immune globulins (HBIg) derived from HBsAg-vaccinated subjects. The anti-HBs-mediated immune pressure on HBV, however, seems to go along with the emergence and/or selection of immune escape HBV mutants that enable viral persistence in spite of adequate antibody titers. These HBsAg escape mutants harbor single or double point mutations that may significantly alter the immunological characteristics of HBsAg. Most escape mutations that influence HBsAg recognition by anti-HBs antibodies are located in the second 'a' determinant loop. Notably, HBsAg with an arginine replacement for glycine at amino acid 145 is considered the quintessential immune escape mutant because it has been isolated consistently in clinical samples of HBIg-treated individuals and vaccinated infants of chronically infected mothers. Direct binding studies with monoclonal antibodies demonstrated a more dramatic impact of this mutation on anti-HBs antibody recognition, compared with other point mutations in this antigenic domain. The clinical and epidemiological significance of these emerging HBsAg mutants will be a matter of research for years to come, especially as data available so far document that these mutants are viable and infectious strains. Strategies for vaccination programs and posttransplantation prophylaxis of recurrent hepatitis need to be developed that may prevent immune escape mutant HBV from spreading and to prevent these strains from becoming dominant during the next decennia.     

抗原抗体复合物型治疗性疫苗(乙克)临床研究中患者血清乙型肝炎病毒表面抗原下降的分析与启示

近年来全球慢性乙型肝炎(chronic hepatitis B,CHB)防治指南提出了“功能性治愈”(functional cure)的概念,即患者经过治疗达到血清乙型肝炎病毒表面抗原(hepatitis B virus surface antigen,HBsAg)消失,但现有抗病毒治疗很难实现这一目标。本研究对既往临床试验中经抗原抗体复合物型治疗性疫苗(乙克)治疗后的CHB患者HBsAg下降情况进行了归纳分析,结果显示,经乙克治疗随访后达到乙型肝炎e抗原(hepatitis B e antigen,HBeAg)血清学转换者的HBsAg下降高达0.95log₁₀IU/mL,显著高于未达到HBeAg血清学转换者的0.32log₁₀IU/mL(P<0.01),而经氢氧化铝佐剂治疗随访后发生HBeAg血清学转换(0.49log₁₀IU/mL)者与未发生HBeAg血清学转换者(0.36log₁₀IU/mL)之间HBsAg下降无统计学差异。乙克组治疗过程中,丙氨酸氨基转移酶(alanine aminotransferase,ALT)骤升(ALT flare)在HBsAg下降>1.0log₁₀IU/mL者中较多见,氢氧化铝组未观察到此现象。回归分析显示,乙克治疗后HBsAg下降的影响因素有患者出现HBeAg血清学转换、感染的HBV为B基因型、治疗过程中ALT出现10倍增高,以及基线血清HBsAg为高水平。结果提示,乙克诱导的特异性免疫对降低CHB患者血清HBsAg水平有一定效果,采用“抗病毒药物治疗＋针对HBsAg的中和性抗体被动免疫＋乙克主动免疫”的“三明治”治疗策略可能会提高“功能性治愈”率。     

Removing N-terminal sequences in pre-s1 domain enhanced antibody and B-cell responses by an HBV large surface antigen DNA vaccine

Although the use of recombinant hepatitis B virus surface (HBsAg) protein vaccine has successfully reduced global hepatitis B infection, there are still a number of vaccine recipients who do not develop detectable antibody responses. Various novel vaccination approaches, including DNA vaccines, have been used to further improve the coverage of vaccine protection. Our previous studies demonstrated that HBsAg-based DNA vaccines could induce both humoral and CMI responses in experimental animal models. However, one form of the the HBsAg antigen, the large S antigen (HBs-L), expressed by DNA vaccine, was not sufficiently immunogenic in eliciting antibody responses. In the current study, we produced a modified large S antigen DNA vaccine, HBs-L(T), which has a truncated N-terminal sequence in the pre-S1 region. Compared to the original HBs-L DNA vaccine, the HBs-L(T) DNA vaccine improved secretion in cultured mammalian cells and generated significantly enhanced HBsAg-specific antibody and B cell responses. Furthermore, this improved HBsL DNA vaccine, along with other HBsAg-expressing DNA vaccines, was able to maintain predominantly Th1 type antibody responses while recombinant HBsAg protein vaccines produced in either yeast or CHO cells elicited mostly Th2 type antibody responses. Our data indicate that HBsAg DNA vaccines with improved immunogenicity offer a useful alternative choice to recombinant protein-based HBV vaccines, particularly for therapeutic purposes against chronic hepatitis infection where immune tolerance led to poor antibody responses to S antigens.     

Expression, purification and characterization of the Hepatitis B virus entire envelope large protein in Pichia pastoris

The current HBsAg vaccine has performed a vital role in preventing the transmission of HBV during the past 20 years. However, a number of individuals still show no response or a low response to the vaccine. In the present study, the HBV envelope large protein gene was cloned into the eukaryotic expression vector pPIC9k and was subsequently expressed in the yeast Pichia pastoris. The HBV large protein (L protein) was produced and secreted into the medium, where some of the L protein formed particles. The soluble L protein and particles were purified by column chromatography and sucrose density gradient centrifugation. Western blot analysis demonstrated that the particle was composed of both HBV L and S protein. To compare the antigenicity of the L protein and HBsAg, rabbits were immunized with the soluble L protein and the commercially available HBV vaccine and the increasing level of antibodies was determined by ELISA. The results showed that the anti-HBsAg antibody, from rabbits injected with the L protein at a dose of 2 and 10microg, was detected on day 14, whereas rabbits vaccinated with 10 and 2microg HBsAg did not develop antibodies until day 21 and 28, respectively. The antibody level in groups inoculated with the L protein was approximately 50% higher than in the group injected with HBsAg using the same dose. Furthermore, 2microg L protein induced a significant and rapid anti-HBsAg antibody response than 10microg HBsAg. Therefore, we suggest that the L protein is an ideal candidate for a new generation HB vaccine to protect people from HBV infection.     

Improvement of hepatitis B virus DNA vaccines by plasmids coexpressing hepatitis B surface antigen and interleukin-2.

DNA vaccines encoding a viral protein have been shown to induce antiviral immune responses and provide protection against subsequent viral challenge. In this study, we show that the efficacy of a DNA vaccine can be greatly improved by simultaneous expression of interleukin-2 (IL-2). Plasmid vectors encoding the major (S) or middle (pre-S2 plus S) envelope proteins of hepatitis B virus (HBV) were constructed and compared for their potential to induce hepatitis B surface antigen (HBsAg)-specific immune responses with a vector encoding the middle envelope and IL-2 fusion protein or with a bicistronic vector separately encoding the middle envelope protein and IL-2. Following transfection of cells in culture with these HBV plasmid vectors, we found that the encoded major protein was secreted while the middle protein and the fusion protein were retained on the cell membrane. Despite differences in localization of the encoded antigens, plasmids encoding the major or middle proteins gave similar antibody and T-cell proliferative responses in the vaccinated animals. The use of plasmids coexpressing IL-2 and the envelope protein in the fusion or nonfusion context resulted in enhanced humoral and cellular immune responses. In addition, the vaccine efficacy in terms of dosage used in immunization was increased at least 100-fold by coexpression of IL-2. We also found that DNA vaccines coexpressing IL-2 help overcome major histocompatibility complex-linked nonresponsiveness to HBsAg vaccination. The immune responses elicited by HBV DNA vaccines were also modulated by coexpression of IL-2. When restimulated with antigen in vitro, splenocytes from mice that received plasmids coexpressing IL-2 and the envelope protein produced much stronger T helper 1 (Th1)-like responses than did those from mice that had been given injections of plasmids encoding the envelope protein alone. Coexpression of IL-2 also increased the Th2-like responses, although the increment was much less significant.     

A rapid and sensitive method based on magnetic beads for the detection of hepatitis B virus surface antigen in human serum

Current clinically assays, such as enzyme‐linked immunosorbent assay and chemiluminescence immunoassay, for hepatitis B surface antigen (HBsAg) are inferior in terms of either sensitivity and accuracy or rapid and high‐throughput analysis. A novel assay based on magnetic beads and time‐resolved fluoroimmunoassay was developed for the quantitative determination of HBsAg in human serum. HBsAg was captured using two types of anti‐HBsAg monoclonal antibodies (B028, S015) immobilized on to magnetic beads and detected using europium‐labeled anti‐HBsAg polyclonal detection antibody. Finally, the assay yielded a high sensitivity (0.02 IU/mL) and a wide dynamic range (0.02–700 IU/mL) for HBsAg when performed under optimal conditions. Satisfactory accuracy, recovery and specificity were also demonstrated. The intra‐ and interassay coefficients of variation were 4.7–8.7% and 3.8–7.5%, respectively. The performance of this assay was further assessed against a well‐established commercial chemiluminescence immunoassay kit with 399 clinical serum samples. It was revealed that the test results for the two methods were in good correlation (Y = 1.182X – 0.017, R = 0.989). In the current study, we demonstrated that this novel time‐resolved fluoroimmunoassay could be used: as a highly sensitive, automated and high‐throughput immunoassay for the diagnosis of acute or chronic hepatitis B virus infection; for the screening of blood or organ donors; and for the surveillance of persons at risk of acquiring or transmitting hepatitis B virus. Copyright © 2013 John Wiley & Sons, Ltd.     

Occult hepatitis B virus infection among injecting drug users in the Central-West Region of Brazil

The prevalence of occult hepatitis B virus (HBV) infection was investigated in 149 hepatitis B surface antigen (HBsAg) negative injecting drug users (IDUs) in the Central-West Region of Brazil. Of these individuals, 19 were positive for HBV DNA, resulting in an occult HBV infection prevalence of 12.7% (19/149); six of these 19 individuals had anti-HBV core and/or anti-HBV surface antibodies and 13 were negative for HBV markers. All IDUs with occult hepatitis B reported sexual and/or parenteral risk behaviours. All HBV DNA-positive samples were successfully genotyped. Genotype D was the most common (17/19), followed by genotype A (2/19). These findings reveal a high prevalence of occult HBV infection and the predominance of genotype D among IDUs in Brazil''s Central-West Region.     

A Human Monoclonal Antibody against Hepatitis B Surface Antigen with Potent Neutralizing Activity

We describe the production and characterization of human monoclonal antibodies (mAb) specific for the major hepatitis B virus (HBV) S protein. The mAbs, two IgG1κ and one IgG1λ, were secreted by B-cell clones obtained from peripheral blood mononuclear cells (PBMC) of one person convalescent from acute hepatitis B and one vaccinated individual. The former recognized a denaturation-insensitive epitope within the p24 protein whereas the latter recognized a denaturation-sensitive, conformational epitope located within the HBsAg common “a” determinant. This mAb, denominated ADRI-2F3, displayed a very high protective titer of over 43,000 IU/mg mAb and showed an extremely potent neutralizing activity in the in vitro model of HBV infection using primary hepatocytes from Tupaia belangeri as target. Recombinant variable heavy and light domain sequences derived from mAb ADRI-2F3 were cloned into eukaryotic expression vectors and showed identical fine specificity and 1 log₁₀ higher titer than the original IgG1λ. It is envisaged that such mAb will be able to efficiently prevent HBV reinfection after liver transplantation for end-stage chronic HBV infection or infection after needle-stick exposure, providing an unlimited source of valuable protective anti-HBs antibody.     

不同佐剂对含S+PreS1融合抗原的乙型肝炎病毒颗粒疫苗免疫原性的影响

本研究在前期工作基础上,用CHO细胞表达的含PreS1+S融合抗原的新型基因工程HBV颗粒疫苗(HBSS1)与Al(OH)3、CpG及CpG+Al(OH)3等佐剂配伍,在Balb/C小鼠模型上研究不同佐剂对HBV颗粒疫苗肌肉注射后免疫应答的影响,主要包括抗体滴度、抗体亚型分类及特异性细胞免疫(γ-IFNELISpot检测)。结果表明:CpG佐剂结合HBSS1颗粒疫苗可快速诱导(单针免疫)高水平的抗PreS1及S抗体,IgG2a/IgG1比率1,同时可诱导较高抗原特异的细胞免疫应答;Al(OH)3+CpG双佐剂组一次免疫后可诱导产生最高的抗S抗体滴度(1:105),其产生的抗体亚类包括IgG1、IgG2a与IgG2b;在S抗原N端(13~49aa)存在优势CTL表位。结论:CpG佐剂结合HBSS1颗粒疫苗应是发展新型治疗性乙肝疫苗的较佳选项。     

Inhibition of the replication of hepatitis B virus in vitro by a novel 2,6-diaminopurine analog, beta-LPA

Antiviral therapy of chronic hepatitis B remains a major clinical problem worldwide. Like lamivudine, nucleoside analogs have become the focus of investigation of anti-hepatitis B virus (anti-HBV) drugs. Here, β-LPA is a novel 2,6-diaminopurine analog found to possess potent anti-HBV activity. In HepG2.2.15 cell line, β-LPA had a 50% effective concentration (EC₅₀) of 0.01 μM against HBV, as determined by analysis of secreted and intracellular episomal HBV DNA. Levels of HBV surface antigen (HBsAg) and e antigen (HBeAg) in drug-treated cultures revealed that β-LPA had no significant inhibitory effects on HBsAg and HBeAg. β-LPA didn’t show any cytotoxicity up to 0.4 μM with a 50% cytotoxic concentration (CC₅₀) of 50 μM. Furthermore, treatment with β-LPA resulted in no apparent inhibitory effects on mitochondrial DNA content. Considering the potent inhibition of HBV DNA synthesis and no obvious toxicity of β-LPA, this compound should be further explored for development as an anti-HBV drug.     

Immunogenicity of recombinant hepatitis B virus surface antigen fused with preS1 epitopes expressed in rice seeds

To test the possibility of producing a novel hepatitis B vaccine in plants, the modified hepatitis B virus (HBV) surface antigen (HBsAg) gene SS1 was expressed in rice under the control of the seed-specific Glub-4 promoter. The SS1 gene encodes a fusion protein consisting of amino acids 21-47 of the hepatocyte receptor-binding presurface 1 region (preS1) fused to the truncated C-terminus of the major HBV surface (S) protein. The production of antibodies against the preS1 region acts to protect humans against HBV infection by preventing HBV from binding to hepatocytes. The presence of SS1 in the genome of transgenic rice was confirmed by PCR and Southern blot analysis, and RNA dot blot analysis indicated that the fused SS1 gene was specifically expressed in rice seeds, with the highest expression level being about 31.5 ng/g dry weight grain. Western blot analysis revealed that the recombinant SS1 protein could be specifically recognized by both an anti-S protein antibody and an anti-preS1 antibody. The recombinant SS1 protein was also observed to form virus-like particles with a diameter of about 22 nm and a density of 1.25 g cm(-3). Furthermore, immunological responses against both the S and preS1 epitopes were induced in BALB/c mice immunized with the recombinant SS1 protein, indicating that this rice-derived SS1 protein could be a promising candidate as an alternative HBV vaccine for preventing hepatitis B.     

Consolidation treatment needed for sustained HBsAg-negative response induced by interferon-alpha in HBeAg positive chronic hepatitis B patients

Hepatitis B surface antigen (HBsAg) clearance is considered as functional cure in patients with chronic hepatitis B (CHB). This study aimed to assess the durability of HBsAg clearance achieved by interferon-based therapies in patients with CHB who were originally positive for hepatitis B envelope antigen (HBeAg). In this prospective study, HBeAg-positive CHB patients with confirmed HBsAg loss under interferon-based therapies were enrolled within 12 weeks from end of treatment and followed up for 48 weeks. Virological markers, biochemical indicators, and liver imaging examinations were observed every 3-6 months. Sustained functional cure was analysed as primary outcome. Factor associated with sustained HBsAg loss or reversion was also investigated. The rate of HBsAg loss sustainability was 91.8% (212/231). Patients receiving consolidation treatment for 12-24 weeks or ≥ 24 weeks had higher rates of sustained HBsAg negativity than those receiving consolidation treatment for < 12 weeks (98.3% and 91.2% vs. 86.7%, P=0.068), and the former groups had significantly higher anti-HBs levels than the later (P < 0.05). The cumulative incidence of HBsAg reversion and HBV DNA reversion was 8.2% and 3.9%, respectively. Consolidation treatment of ≥ 12 weeks[odd ratio (OR) 3.318, 95% confidence interval (CI) 1.077-10.224, P=0.037) was a predictor of sustained functional cure, and HBeAg-positivity at cessation of treatment (OR 12.271, 95% CI 1.076-139.919, P=0.043) was a predictor of HBsAg reversion. Interferon-alpha induced functional cure was durable and a consolidation treatment of ≥ 12-24 weeks was needed after HBsAg loss in HBeAg-positive CHB patients.     

Impairment of hepatitis B virus virion secretion by single-amino-acid substitutions in the small envelope protein and rescue by a novel glycosylation site

Mutations in the S region of the hepatitis B virus (HBV) envelope gene are associated with immune escape, occult infection, and resistance to therapy. We previously identified naturally occurring mutations in the S gene that alter HBV virion secretion. Here we used transcomplementation assay to confirm that the I110M, G119E, and R169P mutations in the S domain of viral envelope proteins impair virion secretion and that an M133T mutation rescues virion secretion of the I110M and G119E mutants. The G119E mutation impaired detection of secreted hepatitis B surface antigen (HBsAg), suggesting immune escape. The R169P mutant protein is defective in HBsAg secretion as well and has a dominant negative effect when it is coexpressed with wild-type envelope proteins. Although the S domain is present in all three envelope proteins, the I110M, G119E, and R169P mutations impair virion secretion through the small envelope protein. Conversely, coexpression of just the small envelope protein of the M133T mutant could rescue virion secretion. The M133T mutation could also overcome the secretion defect caused by the G145R immune-escape mutation or mutation at N146, the site of N-linked glycosylation. In fact, the M133T mutation creates a novel N-linked glycosylation site ((131)NST(133)). Destroying this site by N131Q/T mutation or preventing glycosylation by tunicamycin treatment of transfected cells abrogated the effect of the M133T mutation. Our findings demonstrate that N-linked glycosylation of HBV envelope proteins is critical for virion secretion and that the secretion defect caused by mutations in the S protein can be rescued by an extra glycosylation site.