Papillomavirus pseudovirions packaged with the L2 gene induce cross-neutralizing antibodies

Abstract

Background: Current vaccines against HPVs are constituted of L1 protein self-assembled into virus-like particles (VLPs) and they have been shown to protect against natural HPV16 and HPV18 infections and associated lesions. In addition, limited cross-protection has been observed against closely related types. Immunization with L2 protein in animal models has been shown to provide cross-protection against distant papillomavirus types, suggesting that the L2 protein contains cross-neutralizing epitopes. However, vaccination with L2 protein or L2 peptides does not induce high titers of anti-L2 antibodies. In order to develop a vaccine with the potential to protect against other high-risk HPV types, we have produced HPV58 pseudovirions encoding the HPV31 L2 protein and compared their capacity to induce cross-neutralizing antibodies with that of HPV L1 and HPV L1/L2 VLPs.

Methods: The titers of neutralizing antibodies against HPV16, HPV18, HPV31 and HPV58 induced in Balb/c mice were compared after immunization with L2-containing vaccines.

Results: Low titers of cross-neutralizing antibodies were detected in mice when immunized with L1/L2 VLPs, and the highest levels of cross-neutralizing antibodies were observed in mice immunized with HPV 58 L1/L2 pseudovirions encoding the HPV 31 L2 protein.

Conclusions: The results obtained indicate that high levels of cross-neutralizing antibodies are only observed after immunization with pseudovirions encoding the L2 protein. HPV pseudovirions thus represent a possible new strategy for the generation of a broad-spectrum vaccine to protect against high-risk HPVs and associated neoplasia.

Figure 1

Western blot. A/Analysis by Western blotting of the HPV58 pseudovirion capsid proteins. L1 was detected using the CamVir-1 monoclonal anti body (lane 1). L2 was detected using polyclonal anti-HPV16 L2 rabbit antiserum (lane 2). B/Detection of L2 protein by Western blotting using polyclonal anti-HPV16 L2 rabbit antiserum.Cos-7 cells were transduced with HPV58 pseudovirions encoding GFP (lane 1) or with HPV58 pseudovirion encoding HPV31 L2 (lane 2).

Figure 2

Detection of HPV16, HPV18, HPV31 and HPV58 neutralizing antibodies. The individual mouse neutralizing titers are the means of the last reciprocal dilution providing more than 50% inhibition of luciferase expression. Animals without detectable antibody titers (< 25, dotted line) were assigned a titer of 1 for calculation of GMTs (horizontal bars).