We considered humanizing E16 or E34 as a possible therapeutic measure. Humanized monoclonal antibodies have substantially longer half-lives in humans than their mouse counterparts 26, 27 . Sequencing studies indicated that E16 had greater homology to human framework regions, making it simpler to construct a humanized version of E16. We amplified the cDNA encoding the heavy (VH) and light (VL) variable domains from the hybridoma cellular RNA by a 5′ rapid amplification of cDNA ends (RACE) procedure. The VH belongs to mouse heavy chain subgroup II (J558 family) and the VL belongs to mouse κ chain subgroup V. The complementarity-determining regions of E16 were grafted onto the human VH1-18 backbone (Fig. 4a) and human Vκ-B3 backbone (Fig. 4b) to create Hm-E16.1. One (VL-Y49S) and two framework back-mutations (VH-T71A and VL-Y49S) were introduced to create two variants, Hm-E16.1 and Hm-E16.3, respectively. The resulting humanized VH and VL were combined with human γ1 and κ constant regions, fused to an IgG signal sequence and inserted into expression plasmids. To construct the chimerized antibodies, the mouse VH and VL sequences were combined with the human γ1 and κ constant regions.