Despite advances in systemic lupus erythematosus (SLE) management, achieving sustained efficacy with minimal treatment burden remains an unmet clinical need. We developed a liver-targeted adeno-associated virus (AAV) encoding a CD19-directed bispecific T-cell engager (CD19BiTE) to enable durable B‑cell depletion, and evaluated its efficacy and safety in a humanized model of lupus.

An AAV vector (AAV‑CD19BiTE) was engineered with a liver‑specific promoter to restrict expression to hepatocytes. In vitro validation included binding, T‑cell activation, and cytotoxicity assays. Biodistribution and preliminary safety were assessed in Balb/c mice. Therapeutic efficacy was evaluated in a humanized SLE model reconstituted with patient‑derived Peripheral Blood Mononuclear Cell (PBMCs), using blinatumomab as a comparator. Mechanistic studies involved flow cytometry, immunofluorescence, and cytokine profiling.

A single infusion of AAV‑CD19BiTE led to liver‑targeted, stable BiTE expression persisting for over 12 weeks, and mediated potent antigen‑specific lysis of CD19⁺ B cells in vitro and in vivo. In the humanized lupus model, this one‑time treatment induced profound and sustained clearance of B cells in peripheral blood and lymphoid organs, and outperformed blinatumomab in the durability of dsDNA autoantibody suppression. Consequently, it ameliorated lupus nephritis and reduced pathological IgG deposition in target organs. The therapeutic effect was driven primarily by CD8⁺ T‑cell cytotoxicity, without evidence of systemic cytokine release or CD4⁺ T‑cell‑mediated hyperinflammation.

We describe a novel long‑acting AAV‑based BiTE platform that enables durable, hepatocyte‑restricted expression of CD19BiTE, resulting in potent and sustained B‑cell depletion in a humanized SLE model. Our findings highlight AAV‑CD19BiTE as a promising one‑time therapeutic strategy with efficacy comparable or superior to conventional BiTE therapy, supporting its further translational development for SLE. If translated, this approach could shift the SLE treatment paradigm from chronic management to a potential one‑time intervention, substantially lowering treatment burden and improving adherence and outcomes, while positioning the liver as an effective “bio‑factory” for systemic immunotherapy.