Chronic hepatitis B virus (HBV) infection is a major health concern worldwide, frequently leading to liver cirrhosis, liver failure, and hepatocellular carcinoma. Evidence suggests that high viral antigen load may play a role in chronicity. Production of viral proteins is thought to depend on transcription of viral covalently closed circular DNA (cccDNA). In a human clinical trial with an RNA interference (RNAi)–based therapeutic targeting HBV transcripts, ARC-520, HBV S antigen (HBsAg) was strongly reduced in treatment-naïve patients positive for HBV e antigen (HBeAg) but was reduced significantly less in patients who were HBeAg-negative or had received long-term therapy with nucleos(t)ide viral replication inhibitors (NUCs). HBeAg positivity is associated with greater disease risk that may be moderately reduced upon HBeAg loss. The molecular basis for this unexpected differential response was investigated in chimpanzees chronically infected with HBV. Several lines of evidence demonstrated that HBsAg was expressed not only from the episomal cccDNA minichromosome but also from transcripts arising from HBV DNA integrated into the host genome, which was the dominant source in HBeAg-negative chimpanzees. Many of the integrants detected in chimpanzees lacked target sites for the small interfering RNAs in ARC-520, explaining the reduced response in HBeAg-negative chimpanzees and, by extension, in HBeAg-negative patients. Our results uncover a heretofore underrecognized source of HBsAg that may represent a strategy adopted by HBV to maintain chronicity in the presence of host immunosurveillance. These results could alter trial design and endpoint expectations of new therapies for chronic HBV.

慢性乙型肝炎病毒（HBV）感染是全球主要的健康问题，经常导致肝硬化，肝衰竭和肝细胞癌。有证据表明，高病毒载量可能在慢性病中起作用。病毒蛋白的产生被认为取决于病毒共价闭合的环状DNA（cccDNA）的转录。在一项基于RNA干扰（RNAi）的靶向HBV转录物治疗的人类临床试验中，未经治疗的HBV e抗原（HBeAg）阳性患者中ARC-520，HBV S抗原（HBsAg）明显降低在HBeAg阴性或长期接受核苷酸（t）病毒复制抑制剂（NUCs）治疗的患者中。HBeAg阳性与更大的疾病风险相关，可能会因HBeAg丢失而适度降低。在慢性感染HBV的黑猩猩中研究了这种意想不到的差异反应的分子基础。几条证据表明，HBsAg不仅从游离cccDNA微型染色体表达，而且从整合到宿主基因组中的HBV DNA产生的转录本表达，HBV DNA是HBeAg阴性黑猩猩的主要来源。在黑猩猩中检测到的许多整合子都缺少ARC-520中小的干扰RNA的靶位点，这解释了HBeAg阴性黑猩猩以及HBeAg阴性患者的反应减少。我们的结果揭示了迄今未被充分认识的HBsAg来源，这可能代表了HBV在存在宿主免疫监测的情况下维持慢性的策略。