Six identical female twins aged 9-13 years will participate. One sib of each twin pair will be given Cervarix according to the 0, 1, 6 month vaccination scheme, while the other sib will be given Gardasil according to the 0, 2, 6 month vaccination scheme. Three blood samples will be taken (the first prior to vaccine administration, the second and third 7 days after dose 2 and 3, respectively). The blood samples will be used to determine: 1) the magnitude the anti-HPV 16 and anti-HPV-18 antibody responses, 2) as well as the cross-reactive pattern of these responses towards related, non-vaccine HPV strains (HPV-31 and -33, and HPV-45). 3) plasmablast isolated from blood taken 7 days after the 3rd dose in the first place (and eventually after the 2nd dose also) will be examined for for the usage of VDJ and VJ segments in the immunoglobulin heavy (VH) and light (VL) heavy and light chains. Gene useg in B cells induced by Cervarix and Gardasil will be compared. Finally the cross-reactive potential of monoclonal antibodies obtained by eukaryotic expression of a series of heavy (VH) and light (VL) chains from single ASC isolated after the 3rd dose of a three-dose schedule of either Cervarix or Gardasil will be examined.