With the F1 antigen, only the plate format yielded positive Fab clones after four rounds of selection with the F1 antigen. Sequencing of the clones confirmed that they were identical and designated as m252. With the V-antigen, the plate and bead format each yielded two positive Fab clones after four rounds of selection with each format. One clone from each format, designated as m253 and m254, respectively, was selected for further analysis. Sequence analysis revealed that m252 has heavy and light chains originated from germlines IGHV1-2*02 and IGKV1-16*01 respectively. M253 originated from IGHV1-18*01 and IGKV1-9*01, while m254 was from IGHV3-43*01 and IGKV1-27*01. The mutational rate ranged from zero to less than 10%. This is typical for antibodies isolated from naïve human libraries by panning against viruses causing acute infection in contrast to neutralizing antibodies selected from immune human libraries by panning against HIV-1, which causes a chronic infection [17] . Each of the clones was then transformed into HB2152 cells and the respective Fab was expressed and purified ( Figure 1a ). After conversion to IgG1 expressing clones, the three antibody clones were transiently transfected into Freestyle HEK 293F cells, and the expressed IgG1s were purified ( Figure 1c ).