The pathogenesis role of T lymphocytes in rheumatoid arthritis (RA) has been extensively studied. Whereas CCR7+ naïve and central memory T (TCM) cells are the predominant T lymphocyte populations in the circulation and lymphoid organs, most T cells in the synovium and synovial fluid of patients with RA are CCR7- effector memory T (TEM) cells, making them a desirable therapeutic target for RA. At rest, human and rat T lymphocytes express low levels of two K+ channels, Kv1.3 and KCa3.1, that regulate plasma membrane potential and the homeostasis of Ca2+, a crucial second messenger in T cell activation. Upon activation, CCR7- TEM cells upregulate Kv1.3 while naïve and TCM cells upregulate KCa3.1. Thus, TEM cells are exquisitely sensitive to inhibition by Kv1.3 blockers. On the contrary, naïve and TCM cells rely on KCa3.1 and escape Kv1.3 blockers. ShK-186 is a potent and selective peptide blocker of Kv1.3 that has been extensively tested in rats, non-human primates, healthy volunteers, and patients with a TEM cell-mediated autoimmune disease in a Phase 1A/B clinical trial. The in vivo safety and efficacy of ShK-186 were demonstrated, like for other biologics, after injections. The delivery of Kv1.3-blocking peptides via the buccal mucosa showed that a transmucosal route of delivery is feasible, albeit with low efficacy. We bioengineered the probiotic Limosilactobacillus reuteri to generate LrS235 that secretes ShK-235. The secreted peptide is functional in blocking Kv1.3 channels and suppressing the activation of TEM lymphocytes in vitro. It crosses from the lumen of the GI tract into the circulation after the oral gavage of healthy rats and displays good bioavailability and pharmacokinetics. Treatment with LrS235 effectively reduces disease severity in a rat model of RA, including joint inflammation, cartilage destruction, and bone damage, without immunogenicity.