Human antibody responses to circulating monkeypox virus emphasise the need for the first mpox-specific vaccine
Authors: Raianna F Fantin, Camila H Coelho
Journal: The Lancet Microbe (2024)

Monkeypox virus (MPXV), responsible for mpox (formerly known as monkeypox), has infected more than 90 000 individuals since its last major outbreak during 2022–23, in countries historically unaffected by the disease (seven countries before 2022, and 116 countries in 2023), which has led WHO to declare mpox a public health emergency of international concern.1WHO2022–23 Mpox (Monkeypox) outbreak: global trends.https://worldhealthorg.shinyapps.io/mpx_global/Date: Nov 20, 2023Date accessed: December 6, 2023Google Scholar The primary route of transmission for the current virus strain is through close or intimate contact;1WHO2022–23 Mpox (Monkeypox) outbreak: global trends.https://worldhealthorg.shinyapps.io/mpx_global/Date: Nov 20, 2023Date accessed: December 6, 2023Google Scholar thus, mpox is moving toward becoming a sexually transmitted disease. MPXV is an Orthopoxvirus, a genus encompassing multiple viruses, including the eradicated variola virus, which causes smallpox. Given that smallpox vaccines have shown protection against mpox in animal models,2Edghill-Smith Y Golding H Manischewitz J et al.Smallpox vaccine-induced antibodies are necessary and sufficient for protection against monkeypox virus.Nat Med. 2005; 11: 740-747Crossref PubMed Scopus (301) Google Scholar during the current outbreak, the JYNNEOS vaccine (also known as Imvamune or Imvanex) has been administered to adults at high risk for MPXV infection. This vaccine is a third-generation, live, non-replicating, modified Ankara strain, developed after the second-generation replicating vaccinia ACAM2000 vaccine and presents substantially fewer adverse effects than the first-generation Dryvax, which was permanently discontinued in the 1970s. Although these three smallpox vaccines can provide substantial cross-protection against MPXV, given the high similarity among orthopoxviruses (96–99%), studies assessing JYNNEOS immunogenicity have revealed low antibody neutralisation levels against MPXV,3Zaeck LM Lamers MM Verstrepen BE et al.Low levels of monkeypox virus-neutralizing antibodies after MVA-BN vaccination in healthy individuals.Nat Med. 2023; 29: 270-278Crossref PubMed Scopus (76) Google Scholar highlighting the variability in antigenic targets among poxviruses, particularly in the emerging MPXV strain (clade IIb). Additionally, reports describing breakthrough infections after two doses of JYNNEOS suggest that a more efficient vaccine might be necessary, especially considering that the adjusted effectiveness rate of JYNNEOS is in the range 36–86%.4Center for Disease Control and PreventionJynneos vaccine effectiveness.https://www.cdc.gov/poxvirus/mpox/cases-data/JYNNEOS-vaccine-effectiveness.htmlDate accessed: October 10, 2023Google Scholar The reason JYNNEOS presents only moderate antibody responses against the circulating mpox strain is unclear, but several characteristics of this virus indicate that MPXV has undergone evolutionary modification, including amino acid mutations in key proteins, suggesting viral evolution and host adaptation. Mutations occur less frequently in MPXV, a DNA virus, than in RNA viruses. Nonetheless, for clade IIb MPXV circulating in 2022–23, several single nucleotide polymorphisms have been described in an unusual mutational pattern consistent with sustainable human-to-human transmission, revealing a potential adaptation.5Isidro J Borges V Pinto M et al.Phylogenomic characterization and signs of microevolution in the 2022 multi-country outbreak of monkeypox virus.Nat Med. 2022; 28: 1569-1572Crossref PubMed Scopus (363) Google Scholar To effectively prevent the transmission of this strain, mpox-specific proteins that have potential functional roles ranging from involvement in the viral attachment system to internalisation, binding, replication, and mediation of immune evasion that might help in establishing an infection should be characterised. Some mpox proteins such as M1R, A29L, B6R, H3L, and A35R have been associated with immune responses within poxviruses and, as a result, are considered potential targets for vaccine development. H3L and A35R have attracted the greatest interest as they have the capacity to elicit robust antibody and B-cell responses in convalescent donors, but not in JYNNEOS-vaccinated individuals, which implicates an infection-driven response.6Yefet R Friedel N Tamir H et al.Monkeypox infection elicits strong antibody and B cell response against A35R and H3L antigens.iScience. 2023; 26105957Summary Full Text Full Text PDF PubMed Scopus (10) Google Scholar,7Cohn H Bloom N Cai GY et al.Mpox vaccine and infection-driven human immune signatures: an immunological analysis of an observational study.Lancet Infect Dis. 2023; 23: 1302-1312Summary Full Text Full Text PDF PubMed Scopus (0) Google Scholar H3L is an antigen expressed in the mature virion form of MPXV, and its main feature is binding host cells and helping to establish an infection. Therefore, antibodies targeting this protein are expected to confer neutralisation responses. A35R, an envelope surface glycoprotein (enveloped virion), facilitates the intracellular spread of viral particles. In addition to having peptides that trigger strong T-cell responses, A35R can elicit neutralising antibody responses. Although the vaccinia ortholog A33R shares great homology with the MPXV counterpart (95·0%), mice vaccinated with a four-antigen prototype (A33, L1, B5, and A27) presented high-affinity monoclonal antibodies targeting A33R, but were unable to bind A35R. These findings suggest that these proteins have differences in amino acid residues in the protective epitopes, underpinning the need for a mpox-specific vaccine.3Zaeck LM Lamers MM Verstrepen BE et al.Low levels of monkeypox virus-neutralizing antibodies after MVA-BN vaccination in healthy individuals.Nat Med. 2023; 29: 270-278Crossref PubMed Scopus (76) Google Scholar,8Golden JW Hooper JW Heterogeneity in the A33 protein impacts the cross-protective efficacy of a candidate smallpox DNA vaccine.Virology. 2008; 377: 19-29Crossref PubMed Scopus (0) Google Scholar Smallpox vaccines have shown in-vitro capacity to reduce MPXV burden through antibody-mediated responses; however, these responses were significantly less pronounced than those observed in infected individuals.6Yefet R Friedel N Tamir H et al.Monkeypox infection elicits strong antibody and B cell response against A35R and H3L antigens.iScience. 2023; 26105957Summary Full Text Full Text PDF PubMed Scopus (10) Google Scholar Moreover, the levels of anti-MPXV circulating IgG are increased in serum samples of convalescent donors, whereas they are moderate in vaccinated individuals.7Cohn H Bloom N Cai GY et al.Mpox vaccine and infection-driven human immune signatures: an immunological analysis of an observational study.Lancet Infect Dis. 2023; 23: 1302-1312Summary Full Text Full Text PDF PubMed Scopus (0) Google Scholar Multiple orthopoxviral antigens into a single vaccine formulation have become a novel approach in preclinical studies conducted for the development of mpox-specific vaccines. This approach has been applied across various vaccine development platforms, including mRNA technology.9Fang Z Monteiro VS Renauer PA et al.Polyvalent mRNA vaccination elicited potent immune response to monkeypox virus surface antigens.Cell Res. 2023; 33: 407-410Crossref PubMed Scopus (10) Google Scholar,10Freyn AW Atyeo C Earl PL et al.An mpox virus mRNA-lipid nanoparticle vaccine confers protection against lethal orthopoxviral challenge.Sci Transl Med. 2023; 15eadg3540Crossref Scopus (2) Google Scholar In particular, compared with mice vaccinated with monovalent formulations, those vaccinated with a multivalent formulation containing A29L, E8L, M1R, A35R, and B6R MPXV proteins showed higher neutralisation titres and were protected from a vaccinia virus challenge.9Fang Z Monteiro VS Renauer PA et al.Polyvalent mRNA vaccination elicited potent immune response to monkeypox virus surface antigens.Cell Res. 2023; 33: 407-410Crossref PubMed Scopus (10) Google Scholar Likewise, bivalent (A35R/M1), trivalent (A35R, B6, M1), and tetravalent (A29L, A35R, B6R, M1R) mRNA MPXV formulations revealed greater protection of mice during a vaccinia virus challenge.10Freyn AW Atyeo C Earl PL et al.An mpox virus mRNA-lipid nanoparticle vaccine confers protection against lethal orthopoxviral challenge.Sci Transl Med. 2023; 15eadg3540Crossref Scopus (2) Google Scholar The animals vaccinated with these formulations achieved 100% survival rates and minimal weight loss. Thus, considering the robust infection-specific antibody responses elicited against A35R and H3L, combining these two antigens in a vaccine platform could be a valuable approach to promote mpox-specific immune responses, especially because the two antigens differ antigenically and structurally and are present in two different viral forms—H3L as mature virion and A35H as an enveloped virion. Thus, defining binding epitopes of human anti-H3L and anti-A35R in the circulating MPXV strain will be crucial for designing a functional mpox-specific human vaccine (appendix p 1). Upon scrutinising B-cell antigenic domains using an online prediction tool that uses FASTA sequences as the input and assigns scores to individual amino acids on the basis of parameters such as hydrophilicity and polarity (BepiPred 3·0), we observed that both the H3L and A35R proteins from clade IIb showed discrete variability within the epitopes when compared with their vaccinia virus homologues. Notably, even a single amino acid difference could modify the size of these epitopes (data not shown). Whether these differences are responsible for changes in immunogenicity in vitro and in vivo needs further investigation. In summary, considering the different forms of the virus (mature and enveloped), most effective formulations will comprise more than one target and, if combined, might promote a more protective and effective response. Moreover, the first human mpox-specific vaccine should target the circulating strain but also provide durable, mucosal-specific, long-term antibody responses to MPXV, which could be facilitated by exploiting novel vaccine platforms, targeting different immunisation sites, or combining selected vaccine adjuvants. We declare no competing interests. This project was partly funded with federal funds from the National Institutes of Health (U19 AI142737, U19 AI168631, U54CA267776). The content of this publication does not necessarily reflect the views or policies of the Department of Health and Human Services, nor does mention of trade names, commercial products, or organisations imply endorsement by the US government. Download .pdf (.23 MB) Help with pdf files Supplementary appendix