Anti-HBsAg antibody mAb19-LS enhances antiviral immunity in humans with chronic hepatitis B

Chronic infection with hepatitis B virus (HBV) is characterized by persistent expression of hepatitis B surface antigen (HBsAg), which is associated with profound immune tolerance. Although nucleos(t)ide analogue therapy effectively suppresses viral replication, it neither eliminates HBV nor reverses virus-specific immune dysfunction. Here, we report the results of two parallel first-in-human, dose-escalation studies evaluating a single infusion of mAb19-LS, a long-acting IgG1 monoclonal antibody targeting HBsAg, in individuals with chronic HBV infection receiving nucleos(t)ide analogue therapy. mAb19-LS was generally safe and well tolerated and induced a mean 11-fold increase in antigen clearance. The magnitude and duration of HBsAg suppression were dependent on both baseline antigen levels and mAb19-LS dose, with suppression maintained for more than 36 weeks in individuals receiving the highest dose. Reduction of circulating HBsAg was associated with uptake of HBsAg–IgG immune complexes by monocytes and dendritic cells and inflammatory reprogramming of these antigen-presenting cells. Notably, proliferation of both CD4 ⁺ and CD8 ⁺ T cells, as well as interferon-γ and TNF-α production in response to HBV antigens, were significantly increased 24 weeks after infusion. Together, these findings demonstrate that mAb19-LS is generally safe and effectively accelerates HBsAg clearance while activating antigen presenting cells and enhancing antiviral T cell responses.