Function-Driven Design of a Surrogate Interleukin-2 Receptor Ligand

We developed an artificial signaling system to enable the assembly of cytokine receptor surrogate ligands. A JAK-STAT5 signaling module—comprising the JAK3-specific γc receptor and a functional IL-2Rβ receptor—was stably expressed in a STAT-deficient cell line. Using a combinatorial antibody library, we screened for receptor binders with selective emphasis on IL-2Rβ affinity. Among various bispecific scaffolds, the single-chain diabody (scDb) format demonstrated superior potency and efficacy, effectively recapitulating native IL-2 ligand activity by inducing functional dimerization of IL-2Rβ and γc receptors. The lead scDb-2d (also termed J9H4) agonist antibody functioned as a surrogate IL-2 receptor ligand, selectively driving Teff and NK cell proliferation and activation.