Generation and Characterization of the Human Anti-HTNV Antibody KJJ4

Hantaan virus (HTNV) is the predominant causative agent of hemorrhagic fever with renal syndrome (HFRS) in China, yet no specific antiviral therapy is currently available. Neutralizing antibodies (NAbs) represent a promising strategy, but most existing anti-HTNV NAbs are heterologous and carry immunogenicity risks. Here, two fully human antibodies from a previously established human anti-HTNV phage display library were generated and characterized. KJJ3, a VL-VL tandem antibody derived from clone 3-12, showed weak binding to inactivated HTNV and minimal neutralizing activity (IC₅₀ = 27.12 μg/mL). However, KJJ4, an engineered IgG4 antibody derived from clone 4-19 and carrying the S108P hinge mutation to prevent Fab-arm exchange, bound inactivated HTNV antigen and recombinant glycoprotein Gn (residues 19-371) in a dose-dependent manner, with only weak binding to Gc. Surface plasmon resonance yielded an association rate constant of 4.70 × 10³ M^-1s^-1, a dissociation rate constant of 3.06 × 10^-3 s^-1, and an equilibrium dissociation constant of 650 nM for monomeric Gn_19-371. In a Vero E6 focus-reduction microneutralization assay, KJJ4 neutralized HTNV in vitro with an IC₅₀ of 2.879 μg/mL. These data establish KJJ4 as a fully human anti-HTNV antibody with experimentally defined in vitro binding and neutralizing activity, warranting further evaluation in animal models of HTNV infection.