Why do this?
Cervical cancer has become the fourth-most prevalent cancer in women and poses a serious threat to women's health, in 2020, ~ 604,127 women were newly diagnosed with cervical cancer and it claimed ~ 341,831 deaths worldwide1. Studies have shown that the main cause of cervical cancer and other genital cancers is persistent infection of high-risk human papillomavirus (HR-HPV)2. To date, over 450 distinct HPV types have been identified and 25 of which were classified into carcinogenic or potentially carcinogenic HPV types3. There are five HPV vaccines have been licensed, of these, Gardasil 9 offers the most broad protection, and has efficacy against ~90% of cervical cancer induced by 7 types of HR-HPV (HPV16, -18, -31, -33, -45, -52 and -58) as well as against 90% of genital warts induced by two LR-HPV types (HPV6 and -11)4. Despite the broad protection provided by Gardasil 9, approximately 10% of cervical cancer caused by other HR-HPV types still cannot be effectively prevented5. Given non-vaccine HPV types prevailing over Gardasil 9, a next-generation of HPV vaccine should have broader coverage. Recently, immunogen design by immune focus of functional epitopes of multi-genotypic viruses is appealing in the field of broad protective vaccine development, but still lack of methodological blueprint in particular for immunogenicity design.
How can we do?
Rational immunogen design is expected to solve the current challenges in long-unresolved vaccine development6. As well-known in vaccinology, there are two prerequisite attributes for a potent immunogen, i.e. antigenicity based on specific epitope structure and immunogenicity raised from those immunodominant epitopes. The effectiveness of most vaccines depends on neutralizing antibody (nAb) response; however, most immunodominant protective nAbs are type-specific. Therefore, for pathogens that frequently mutate into or have multiple genotypes, such as HPV, it is becoming increasingly important to determine new ways to optimize neutralizing epitopes while achieving broad immune protection. At present, there are several immunogen design strategies in use for the development of broad-spectrum vaccines, such as germline targeting, computationally optimized broadly reactive antigen design (COBRA), consensus sequence construction, and structural biology-based epitope transplantation7,8.
What did we do?
Previous studies on HPV structural biology have shown that the HPV L1 monomer forms a canonical, eight-stranded β-barrel (BIDG-CHEF), and both biochemical and structural analyses demonstrated that HPV type-specificity is associated with the five highly variable surface loops—BC, DE, EF, FG and HI—on the HPV capsid, some of which constitute most of HPV type-specific neutralization sites that could be recognized by potent neutralizing antibodies, including the well-known HPV16.V5, HPV16.U4, HPV16.14J and HPV16.1A9-11. In this study, based on the high structural similarity of L1 surface loops within a group of phylogenetically close HPV types, we constructed a single VLP immunogen by loop-swapping on immunodominant regions of three HPV genotypes, which are not covered in the commercial vaccines. The reaction profile of type-specific antibodies suggests the immunodominant epitopes of HPV types 39, -68 and -70 are separate in VLP surface regions, clustering of which could elicit protective antibodies against all the three serotypes. Therefore, we expanded the rationale of cross-type vaccine design by the linkage of reactogenicity and immunogenicity—separate sites with inter-type similar sequence and structure as well as type-specific immunodominant epitope to be clustered together.
Figure 1. Roadmap of the design of an Escherichia coli-derived triple-type chimeric vaccine against human papillomavirus types 39, 68 and 70.
By virtue of our previous work on HPV VLPs and HPV vaccines, including elucidation on the assembly mechanism of HPV VLP derived from E. coli12; development of the first E. coli-expressed HPV16/18 bivalent vaccine (Cecolin®, marketed in numbers of countries or regions, with WHO PQ) and HPV nonavalent vaccine (in phase III clinical trial)13; and discovery on the structural basis of antibody-mediated HPV type-specific neutralization14, this study is further based on an in-depth understanding of HPV type specificity and obtains a lead candidate chimeric VLP for an HPV39/68/70 triple-type vaccine15. In addition to this study and the early HPV58/33/52 work16, we recently published another HPV26/69/51 chimeric VLP vaccine with GMP-like manufacturing data17. Our next goal is to verify the broad protection by combination of multiple chimeric VLPs in the non-human privates. We set an ultimate destination for developing a multiple type HPV vaccine such as 20 valent with fewer VLPs, which is believed to substantially minimize the production complexity of next-generation HPV vaccine. We also anticipate this strategy could be extrapolated to rational design on other vaccines.
1. WHO. Human Papillomavirus and Related Diseases Report, <https://hpvcentre.net/statistics/reports/XWX.pdf?t=1646934138325> (2021).
2. Egawa, N., Egawa, K., Griffin, H. & Doorbar, J. Human Papillomaviruses; Epithelial Tropisms, and the Development of Neoplasia. Viruses 7, 3863-3890, doi: 10.3390/v7072802 (2015).
3. McBride, A. A. Human papillomaviruses: diversity, infection and host interactions. Nat Rev Microbiol 20, 95-108, doi:10.1038/s41579-021-00617-5 (2022).
4. Printz, C. FDA approves Gardasil 9 for more types of HPV. Cancer 121, 1156-1157, doi:10.1002/cncr.29374 (2015).
5. Dadar, M. et al. Advances in Designing and Developing Vaccines, Drugs and Therapeutic Approaches to Counter Human Papilloma Virus. Frontiers in immunology 9, 2478, doi:10.3389/fimmu.2018.02478 (2018).
6. Havenar-Daughton, C. et al. The human naive B cell repertoire contains distinct subclasses for a germline-targeting HIV-1 vaccine immunogen. Sci Transl Med 10, doi:10.1126/scitranslmed.aat0381 (2018).
7. Scarselli, M. et al. Rational design of a meningococcal antigen inducing broad protective immunity. Sci Transl Med 3, 91ra62, doi:10.1126/scitranslmed.3002234 (2011).
8. Burman, C., Alderfer, J. & Snow, V. T. A review of the immunogenicity, safety and current recommendations for the meningococcal serogroup B vaccine, MenB-FHbp. Journal of clinical pharmacy and therapeutics 45, 270-281, doi:10.1111/jcpt.13083 (2020).
9. Christensen, N. D. et al. Human Papillomavirus Types 6 and 11 Have Antigenically Distinct Strongly Immunogenic Conformationally Dependent Neutralizing Epitopes. Virology 205, 329-335, doi: https://doi.org/10.1006/viro.1994.1649 (1994).
10. Lee, H. et al. A cryo-electron microscopy study identifies the complete H16.V5 epitope and reveals global conformational changes initiated by binding of the neutralizing antibody fragment. J Virol 89, 1428-1438, doi: 10.1128/jvi.02898-14 (2015).
11. Guan, J. et al. Structural comparison of four different antibodies interacting with human papillomavirus 16 and mechanisms of neutralization. Virology 483, 253-263, doi: 10.1016/j.virol.2015.04.016 (2015).
12. Li, Z. et al. The C-Terminal Arm of the Human Papillomavirus Major Capsid Protein Is Immunogenic and Involved in Virus-Host Interaction. Structure 24, 874-885, doi: 10.1016/j.str.2016.04.008 [doi] (2016).
13. Wei, M. et al. N-terminal truncations on L1 proteins of human papillomaviruses promote their soluble expression in Escherichia coli and self-assembly in vitro. Emerging Microbes & Infections 7, 1-12, doi:10.1038/s41426-018-0158-2 (2018).
14. Li, Z. et al. Crystal Structures of Two Immune Complexes Identify Determinants for Viral Infectivity and Type-Specific Neutralization of Human Papillomavirus. MBio 8, doi:10.1128/mBio.00787-17 (2017).
15. Qian, C. et al. Characterization of an Escherichia coli-derived triple-type chimeric vaccine against human papillomavirus types 39, 68 and 70. NPJ vaccines 7, 134, doi:10.1038/s41541-022-00557-y (2022).
16. Li, Z. et al. Rational design of a triple-type human papillomavirus vaccine by compromising viral-type specificity. Nat Commun 9, 5360, doi:10.1038/s41467-018-07199-6 (2018).
17. Yu, M. et al. A bacterially expressed triple-type chimeric vaccine against human papillomavirus types 51, 69, and 26. Vaccine 40, 6141-6152, doi: https://doi.org/10.1016/j.vaccine.2022.09.010 (2022).