Monoclonal antibodies represent half of the top ten selling drugs. Their proven efficacy, however, generally requires repeated administration for prolonged periods of time. In contrast, cell-based therapies offer a different set of pharmacokinetics and pharmacodynamics than traditional medicines, including the potential to have lifetime durability after a single infusion. Here, we describe a genome-engineered stem cell-based platform for continuous antibody production from a single dose. Using CRISPR/Cas9 homology-directed repair mediated editing, we precisely integrated therapeutic antibody expression cassettes into a safe-harbor locus of hematopoietic stem and progenitor cells (HSPCs). Upon differentiation, these gene-targeted HSPCs generate B cells that secrete monoclonal antibodies. We validated this platform using two clinically approved antibodies, achieving efficient targeted integration of the gene-targeted antibodies (GT-Ab) in human HSPCs that successfully engraft in immunodeficient mice. Direct engineering of human B cells demonstrated robust secretion of therapeutic antibodies. To evaluate in vivo antibody production, we transplanted engineered GT-Ab murine HSPCs into immunocompetent mice, achieving durable serum antibody concentrations within the therapeutic range over several months. Lastly, by fusing the antibody to a destabilization domain, we enabled tunable antibody secretion via small molecule regulation. This modular platform establishes a potentially curative approach for chronic diseases currently reliant on repeated antibody administration, offering durable antibody production from a single treatment.