Vaccinia virus strain LC16m8 defective in the B5R gene keeps strong protection comparable to its parental strain Lister in immunodeficient mice

Vaccines against mpox: MVA-BN and LC16m8

INTRODUCTION

Global outbreaks involving mpox clade IIb began in mid-2022. Today, clade IIb and clade I outbreaks continue. Reliable mpox vaccines can prevent serious mpox disease and death.

AREAS COVERED

Globally, two vaccines hold mpox indications, regardless of mpox viral clade: MVA-BN (Bavarian Nordic) and LC16m8 (KM Biologics). This review summarizes the human and pivotal animal data establishing safety and efficacy for MVA-BN and LC16m8, including real-world evidence gathered during mpox outbreaks from 2022 through 2024.

EXPERT OPINION

Some regulatory decisions for MVA-BN and LC16m8 followed pathways based on surrogate outcomes, including lethal-challenge studies in nonhuman primates, among other atypical aspects. Nonetheless, MVA-BN and LC16m8 hold unencumbered registration in multiple countries. Effectiveness of MVA-BN as primary preventive vaccination (PPV) in humans against clade IIb mpox is clear from real-world studies; effectiveness of LC16m8 against clade IIb is likely from surrogate endpoints. Effectiveness of MVA-BN and LC16m8 as PPV against more-lethal clade I is likely, based on animal-challenge studies with multiple orthopoxvirus species and other studies. Both vaccines have solid safety records. MVA-BN's replication incompetence favors adoption, whereas LC16m8 has more pediatric data. Additional real-world evidence, in additional geographic settings and special populations (e.g. pregnancy, immune suppression, atopic dermatitis), is needed.

Construction of a recombinant vaccine expressing Nipah virus glycoprotein using the replicative and highly attenuated vaccinia virus strain LC16m8

Nipah virus (NiV) is a highly pathogenic zoonotic virus that causes severe encephalitis and respiratory diseases and has a high mortality rate in humans (>40%). Epidemiological studies on various fruit bat species, which are natural reservoirs of the virus, have shown that NiV is widely distributed throughout Southeast Asia. Therefore, there is an urgent need to develop effective NiV vaccines. In this study, we generated recombinant vaccinia viruses expressing the NiV glycoprotein (G) or fusion (F) protein using the LC16m8 strain, and examined their antigenicity and ability to induce immunity. Neutralizing antibodies against NiV were successfully induced in hamsters inoculated with LC16m8 expressing NiV G or F, and the antibody titers were higher than those induced by other vaccinia virus vectors previously reported to prevent lethal NiV infection. These findings indicate that the LC16m8-based vaccine format has superior features as a proliferative vaccine compared with other poxvirus-based vaccines. Moreover, the data collected over the course of antibody elevation during three rounds of vaccination in hamsters provide an important basis for the clinical use of vaccinia virus-based vaccines against NiV disease. Trial Registration: NCT05398796.

Highly attenuated poxvirus-based vaccines against emerging viral diseases

Although one member of the poxvirus family, variola virus, has caused one of the most devastating human infections worldwide, smallpox, the knowledge gained over the last 30 years on the molecular, virological and immunological mechanisms of these viruses has allowed the use of members of this family as vectors for the generation of recombinant vaccines against numerous pathogens. In this review, we cover different aspects of the history and biology of poxviruses with emphasis on their application as vaccines, from first- to fourth-generation, against smallpox, monkeypox, emerging viral diseases highlighted by the World Health Organization (COVID-19, Crimean-Congo haemorrhagic fever, Ebola and Marburg virus diseases, Lassa fever, Middle East respiratory syndrome and severe acute respiratory syndrome, Nipah and other henipaviral diseases, Rift Valley fever and Zika), as well as against one of the most concerning prevalent virus, the Human Immunodeficiency Virus, the causative agent of AcquiredImmunodeficiency Syndrome. We discuss the implications in human health of the 2022 monkeypox epidemic affecting many countries, and the rapid prophylactic and therapeutic measures adopted to control virus dissemination within the human population. We also describe the preclinical and clinical evaluation of the Modified Vaccinia virus Ankara and New York vaccinia virus poxviral strains expressing heterologous antigens from the viral diseases listed above. Finally, we report different approaches to improve the immunogenicity and efficacy of poxvirus-based vaccine candidates, such as deletion of immunomodulatory genes, insertion of host-range genes and enhanced transcription of foreign genes through modified viral promoters. Some future prospects are also highlighted.

Smallpox, Monkeypox and Other Human Orthopoxvirus Infections

Considering that vaccination against smallpox with live vaccinia virus led to serious adverse effects in some cases, the WHO, after declaration of the global eradication of smallpox in 1980, strongly recommended to discontinue the vaccination in all countries. This led to the loss of immunity against not only smallpox but also other zoonotic orthopoxvirus infections in humans over the past years. An increasing number of human infections with zoonotic orthopoxviruses and, first of all, monkeypox, force us to reconsider a possible re-emergence of smallpox or a similar disease as a result of natural evolution of these viruses. The review contains a brief analysis of the results of studies on genomic organization and evolution of human pathogenic orthopoxviruses, development of modern methods for diagnosis, vaccination, and chemotherapy of smallpox, monkeypox, and other zoonotic human orthopoxvirus infections.

Monkeypox: epidemiology, pathogenesis, treatment and prevention

Monkeypox is a zoonotic disease that was once endemic in west and central Africa caused by monkeypox virus. However, cases recently have been confirmed in many nonendemic countries outside of Africa. WHO declared the ongoing monkeypox outbreak to be a public health emergency of international concern on July 23, 2022, in the context of the COVID-19 pandemic. The rapidly increasing number of confirmed cases could pose a threat to the international community. Here, we review the epidemiology of monkeypox, monkeypox virus reservoirs, novel transmission patterns, mutations and mechanisms of viral infection, clinical characteristics, laboratory diagnosis and treatment measures. In addition, strategies for the prevention, such as vaccination of smallpox vaccine, is also included. Current epidemiological data indicate that high frequency of human-to-human transmission could lead to further outbreaks, especially among men who have sex with men. The development of antiviral drugs and vaccines against monkeypox virus is urgently needed, despite some therapeutic effects of currently used drugs in the clinic. We provide useful information to improve the understanding of monkeypox virus and give guidance for the government and relative agency to prevent and control the further spread of monkeypox virus.

An increase in glycoprotein concentration on extracellular virions dramatically alters vaccinia virus infectivity and pathogenesis without impacting immunogenicity

The extracellular virion (EV) form of Orthopoxviruses is required for cell-to-cell spread and pathogenesis, and is the target of neutralizing antibodies in the protective immune response. EV have a double envelope that contains several unique proteins that are involved in its intracellular envelopment and/or subsequent infectivity. One of these, F13, is involved in both EV formation and infectivity. Here, we report that replacement of vaccinia virus F13L with the molluscum contagiosum virus homolog, MC021L, results in the production of EV particles with significantly increased levels of EV glycoproteins, which correlate with a small plaque phenotype. Using a novel fluorescence-activated virion sorting assay to isolate EV populations based on glycoprotein content we determine that EV containing either higher or lower levels of glycoproteins are less infectious, suggesting that there is an optimal concentration of glycoproteins in the outer envelope that is required for maximal infectivity of EV. This optimal glycoprotein concentration was required for lethality and induction of pathology in a cutaneous model of animal infection, but was not required for induction of a protective immune response. Therefore, our results demonstrate that there is a sensitive balance between glycoprotein incorporation, infectivity, and pathogenesis, and that manipulation of EV glycoprotein levels can produce vaccine vectors in which pathologic side effects are attenuated without a marked diminution in induction of protective immunity.

Viral glycoproteins are critical determinants of host cell tropism, immunity, and pathogenesis. Vaccinia virus was used for the most successful immunization program in history, and poxviruses continue to be used as vaccine vectors. Here, we report that vaccinia virus extracellular virion (EV) protein F13 plays an important, previously unappreciated, role in controlling glycoprotein incorporation, and that there is a direct relationship between glycoprotein concentrations and subsequent infectivity. Crucially, manipulation of the EV glycoprotein concentrations altered pathogenesis and lethality in an in vivo infection model, but did not markedly alter the induced immune response. These results have important implications that inform the design of safer and more efficacious poxvirus-based vaccine vectors by altering glycoprotein content.

Effect of Serial Passage on the Pathogenicity and Immunogenicity of Vaccinia Virus LC16m8 Strain

The phenotype of an attenuated live vaccine depends on gene mutation achieved by, for example, many passages in cultured cells. Viral clones with preferable phenotypes are selected and the causative genetic mutation(s) are later identified. LC16m8 is an example of a highly attenuated smallpox vaccine that was developed and licensed in Japan in the 1970s. LC16m8 was obtained by the passaging of Lister strain, with indicators of small plaque formation and temperature sensitivity as virus phenotypes. This strain can replicate in mammalian cells and provides robust cellular and humoral immunity, as well as long-term immune memory. Recent studies using proteome-wide antigen arrays have revealed that antibody production against LC16m8 and other VACVs differs largely among individuals. Moreover, associations between SNPs in immune-related genes and immune outcomes have been increasingly found. These results lead to predicting adverse events of a vaccine, which is a purpose of vaccinomics. Studies on VACV will continue to contribute to the understanding of host-pathogen interactions and to development of a vaccine for other infectious and non-infectious diseases. Here, we review studies of VACV, including our recent research on LC16m8, with a focus on the phenotype and genotype, and we discuss future research directions.

Challenges and Achievements in Prevention and Treatment of Smallpox

Declaration of smallpox eradication by the WHO in 1980 led to discontinuation of the worldwide vaccination campaign. The increasing percentage of unvaccinated individuals, the existence of its causative infectious agent variola virus (VARV), and the recent synthetic achievements increase the threat of intentional or accidental release and reemergence of smallpox. Control of smallpox would require an emergency vaccination campaign, as no other protective measure has been approved to achieve eradication and ensure worldwide protection. Experimental data in surrogate animal models support the assumption, based on anecdotal, uncontrolled historical data, that vaccination up to 4 days postexposure confers effective protection. The long incubation period, and the uncertainty of the exposure status in the surrounding population, call for the development and evaluation of safe and effective methods enabling extension of the therapeutic window, and to reduce the disease manifestations and vaccine adverse reactions. To achieve these goals, we need to evaluate the efficacy of novel and already licensed vaccines as a sole treatment, or in conjunction with immune modulators and antiviral drugs. In this review, we address the available data, recent achievements, and open questions.

Are We Prepared in Case of a Possible Smallpox-Like Disease Emergence?

Smallpox was the first human disease to be eradicated, through a concerted vaccination campaign led by the World Health Organization. Since its eradication, routine vaccination against smallpox has ceased, leaving the world population susceptible to disease caused by orthopoxviruses. In recent decades, reports of human disease from zoonotic orthopoxviruses have increased. Furthermore, multiple reports of newly identified poxviruses capable of causing human disease have occurred. These facts raise concerns regarding both the opportunity for these zoonotic orthopoxviruses to evolve and become a more severe public health issue, as well as the risk of Variola virus (the causative agent of smallpox) to be utilized as a bioterrorist weapon. The eradication of smallpox occurred prior to the development of the majority of modern virological and molecular biological techniques. Therefore, there is a considerable amount that is not understood regarding how this solely human pathogen interacts with its host. This paper briefly recounts the history and current status of diagnostic tools, vaccines, and anti-viral therapeutics for treatment of smallpox disease. The authors discuss the importance of further research to prepare the global community should a smallpox-like virus emerge.

Defending against smallpox: a focus on vaccines

Smallpox has shaped human history, from the earliest human civilizations well into the 20th century. With high mortality rates, rapid transmission, and serious long-term effects on survivors, smallpox was a much-feared disease. The eradication of smallpox represents an unprecedented medical victory for the lasting benefit of human health and prosperity. Concerns remain, however, about the development and use of the smallpox virus as a biological weapon, which necessitates the need for continued vaccine development. Smallpox vaccine development is thus a much-reviewed topic of high interest. This review focuses on the current state of smallpox vaccines and their context in biodefense efforts.

Freeze-dried live attenuated smallpox vaccine prepared in cell culture "LC16-KAKETSUKEN": Post-marketing surveillance study on safety and efficacy compliant with Good Clinical Practice

BACKGROUND

In Japan, production of smallpox vaccine LC16m8 (named LC16-KAKETSUKEN) was restarted and was determined to be maintained as a national stockpile in March 2002.

OBJECTIVE

To conduct a post-marketing surveillance study of the vaccination of freeze-dried live attenuated smallpox vaccine prepared in cell culture LC16-KAKETSUKEN using attenuated vaccinia strain LC16m8. The study complied with Good Clinical Practice, focusing on a comparison between primary vaccinees and re-vaccinees.

METHOD

268 personnel (261 males and 7 females) of the Japan Ground Self-Defense Force were inoculated with LC16-KAKETSUKEN and thereafter adverse events and efficacy were evaluated.

RESULTS

Among 268 vaccinee participants, the following vaccinees showed adverse events, none serious: 53 of 196 primary vaccinees (without previous smallpox vaccination), 4 of 71 re-vaccinees (with previous smallpox vaccination) and 1 vaccinee with unknown previous vaccination history. A breakdown of adverse events observed in this study (total 268 vaccinees) showed the following minor or mild adverse events: 52 (19.4%) swelling of axillary lymph node, 4 (1.5%) fever, 2 (0.7%) fatigue, 1 (0.4%) of rash, 14 (5.2%) erythema at the inoculation site, 1 (0.4%) swelling at the inoculation site and 1 (0.4%) autoinoculation. The incidence of adverse events for primary vaccinees (53/196; 27.0%) was significantly higher than for re-vaccinees (4/71; 5.6%). However, the proportion of vaccine take was significantly higher for primary vaccinees (185/196; 94.4%) than for re-vaccinees (58/71; 81.7%). Although the proportion of vaccine take of re-vaccinees was significantly lower than for primary vaccinees due to preexisting immunity by previous vaccination, no significant difference was found in neutralizing antibody titers between primary vaccinees and re-vaccinees at 1, 4 and 7 months after LC16-KAKETSUKEN vaccination.

CONCLUSION

The present post-marketing surveillance study compliant with Good Clinical Practice demonstrated the efficacy and safety of the smallpox vaccine LC16-KAKETSUKEN in an adult population. LC16-KAKETSUKEN is the sole currently available licensed smallpox vaccine for both adult and pediatric populations.