Murine mAbs have been shown to have limited clinical use because of their short serum half-life, inability to trigger human effector functions and the production of human anti-murine antibodies (HAMA) response [46] . mAbs have been humanized by grafting their CDRs onto the V H and V L FRs of human Ig molecules [47] . DB32-6 was the most potent mAb against DENV-2 and showed potential as a therapeutic antibody. To develop humanized mAbs, we sequenced V H and V L segment of the neutralizing mAbs from hybridoma cell lines. The CDRs of DB32-6 were grafted onto human IgG1 backbone to create humanized DB32-6 (hDB32-6) ( Figure 5A ). The hDB32-6 was expressed in CHO-K1 cells and purified from culture supernatants. Both hDB32-6 and mDB32-6 were able to against DENV-2 ( Figure 5B ). The hDB32-6 maintained the specificity of murine DB32-6 (mDB32-6). Furthermore, we established stable clones of hDB32-6. After selection, mAbs hDB32-6-30, hDB32-6-48 and hDB32-6-51 were found to have highly binding activity ( Figure 5C ). Comparing to these mAbs, we found hDB32-6-48 to have the highest production rate in cells. mAb hDB32-6-48 was dose-dependent against DENV-2 and E-DIII ( Figure 5D ). The affinity was analyzed by surface plasmon resonance. The mDB32-6 and hDB32-6-48 bound to E-DIII of DENV-2 with a similar affinity (0.12 nM and 0.18 nM, respectively) ( Figure 5E ). The results revealed that hDB32-6 maintained the same binding affinity to the E protein as mDB32-6. mAb hDB32-6 protected mice from DENV-2-induced mortality