Differences and similarities between our work and those of Varsani, et al. (J. Virol 2003: 77; 8386-8393) Yoshihiko Murata, University of Rochester School of Medicine and Dentistry 8 September 2009 We do note that Varsani, et al. (J. Virol 2003: 77; 8386-8393) have previously engineered a single 13 aa neutralizing epitope from HPV 16 L2 protein within various regions of the HPV 16L1 protein. One of their L1 derivatives (ChiΔF-L2) bore the L2 epitope as a substitution of aa 414-426, which maps to the L1 helix 4 (h4) domain. As we have found with our capsomere derivatives, ChiΔF-L2 reacts slightly more strongly with H16:V5 mAb in ELISAs as compared to intact 16L1 VLPs. When injected into laboratory mice, ChiΔF-L2 was the most immunogenic among the various L1-L2 chimeras with respect to the L2 epitope and as assayed by immunoblots to detect reactogenicity against bacterially derived L2 protein; our findings confirm their assertion that h4 region is “probably highly immunogenic” (p. 8392). There are no data reported on the HPV pseudoneutralization capacities of the resulting sera. However, our constructions differ from that of Varsani, et al. in that: 1) using baculovirus-derived L1 derivatives, we confirm previous results from bacterially derived L1 deletions that the removal of a larger portion of L1 (aa 404-436) results in capsomere formation; and 2) we demonstrate that the replacement of such a deletion with one of two neutralizing epitopes of varying length and predicted in-solution structure (aa 255-278, which forms a helix-coil-helix, and aa 423-436, a linear epitope) of the respiratory syncytial virus (RSV) fusion (F) protein also leads to capsomeres with some degree of aggregation as confirmed by sucrose gradient ultracentrifugation. Thus, we show that the larger h4 deletion that that used to generate ChiΔF-L2 can accommodate the presence of heterologous aa sequences with minimal to moderate ultrastructural perturbations of L1 capsomeres. In generating our constructions, we removed the L1 Cys 428, which is involved in intercapsomeric disulfide bond formation and is retained in ChiΔF-L2. We also note that as compared to electron micrographs of our capsomere preparations, those of ChiΔF-L2 qualitatively appear to exhibit increased degree of aggregation (Figure 2, p. 8389); no assays of in-solution behavior of ChiΔF-L2 are presented. Such aggregation may be related to residual and potentially aberrant disulfide formation among L1 oligomers via Cys428 within each L1 monomer. Thus, in our current paper, we confirm and extend previous finding by Varsani, et al. Competing interests YM, RCR, and EEW are authors of a provisional patent application on the use of human papillomavirus L1 protein and its derivatives, including capsomeres, as RSV vaccine candidates. This is clearly stated in our paper and is reproduced here.