T cell immunity independent HBV clearance and validation of a new HBV cure strategy in HBV infected uPA/SCID chimeric mice

Abstract

Background: Chronic HBV infection is maintained by HBV cccDNA. Evidence suggests that cccDNA persistence is maintained by cccDNA replenishment mainly through de novo infection. We aimed to test a new HBV cure strategy that constantly blocks new rounds of infection in HBV infected animal model with anti-HBs antibody. A prerequisite for establishing HBV cure with this new strategy is that infected livers must undergo spontaneous clearance. Methods: An optimized AAV vector was used to express sustained high level of anti-HBs. HBV infected uPA/SCID mice with null T and B cell immunity and viremia >1E8 HBV DNA copies/ml, were treated with AAV vector expressing malaria antibody or anti-HBs antibodies 7-week post inoculation. Serum HBV DNA and HBsAg level were monitored and liver HBV DNA including cccDNA level was determined through random sampling of each autopsied liver 20 times. Results: > 100ug/mL expressed antibodies were detected in week 3 after a single injection of 1E11 genome copies of each AAV vector and sustained for at least 250-day. There are two key findings: 1. T cell immunity independent clearance. Viremia in HBV infected animals can experience up to 10-fold drop for a few weeks, indicating a portion of infected cells spontaneously clear HBV infection. Viremia in animals treated with anti-HBs antibody was up to >100-fold lower than that with expressing malaria antibody, suggesting the presence of T cell immunity-independent clearance and de novo infection after all infectible liver cells infected. 2. Validation of new HBV cure strategy. Intervention with anti-HBs antibody reproduce two HBV cure courses resembling acute HBV infection, one group of animals (n=9) started progressive viremia reduction for up to 24-fold after reaching peak viremia (>3E10 copies/ml) and the other group (n=6) aborted peak infection with >100-fold lower viremia and 46-fold lower HBsAg level compared to animals with expressed malaria antibody. HBV DNA and HBsAg in one of 6 animals became undetectable for >3 months and cccDNA was only detected in 2 of 19 liver samplings (average 0.036 copies/cell and 0.008 copies/cell in two positive samplings), while cccDNA was detected in all 20 sampling with average 10.8 cccDNA copies/cell in an animal treated with malaria antibody. Conclusion: 1. T cell immunity-independent HBV clearance occurs, and it services a foundation for establishing HBV cure in HBV infected human livers of chimeric mice. 2. Constantly blocking de novo infection with engineered humoral immunity that remedies absent anti-HBs significantly lowers HBV infection and cccDNA level and reproduces two HBV cure courses resembling resolution courses in acute HBV infection.

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