Monkeypox virus (monkeypox, MPXV) was first identified in non-human primates in the late 1950s. Monkeypox, a zoonotic disease, was first found in monkeys used in the study in 1958 and spread mainly among animals. Human monkeypox cases were first found in the Democratic Republic of the Congo in 1970. Since then, monkeypox has been endemic in a number of African countries, including Nigeria, the Democratic Republic of the Congo, and the Central African Republic.
Since the cessation of smallpox vaccination, the monkeypox virus has been self-limiting in populations in Central and West Africa. In 2003, wild rodent imports led to an outbreak of the monkeypox virus in the United States, infecting more than 70 people and even directly causing a young child to be hospitalized. In the past, due to the limited human-to-human transmission capacity of the monkeypox virus, these outbreaks were quickly contained. Today, the transmission capacity of the monkeypox virus is increasing, and monkeypox has broken out in more than 29 countries around the world, resulting in nearly 80,000 infections and 52 deaths, bringing new challenges to world health and public safety.
Recently, Bernard Moss et al. uploaded an article on bioRxiv: A monkeypox mRNA-lipid nanoparticle vaccine targeting virus binding, entry, and transmission drives protection against a lethal orthopoxviral challenge to determine whether the mRNA vaccine encoding four highly conserved surface proteins of the monkeypox virus can induce the same immune protective effect as the MVA attenuated vaccine.
Antigen Design of mRNA Vaccines against the Monkeypox Virus
Considering the complex life cycle of the vaccinia virus, the vaccinia virus antigen contains two antigens from MV (A27 and L1) and EV (B5 and A33) to provide immune protection, so four monkeypox virus antigens with amino acid sequence similarity of 94.6%, 98.4%, 96.5%, and 95% are selected as vaccine antigens: A29, M1, B6, and A35. The researchers modified four monkeypox virus antigens to improve antigen expression efficiency: A29 is a secretory protein with a signal peptide from influenza virus H1 and removed all N-linked glycosylation sites and Cys. The signal peptide from influenza virus H1 was added to the M1 protein sequence to mutate the Ser/Thr in the M1 protein sequence to Ala, thereby removing all N-linked glycosylation sites, truncating the cytoplasmic domain of the M1 protein sequence (after residue 208), and truncating the cytoplasmic domain of the B6 protein (after residue 303). The N-terminal transmembrane domain from influenza virus N2 was added to the A35 protein sequence to replace the wild-type cytoplasmic and transmembrane domains (the first 59 amino acids). Flow cytometry showed that the expression of the modified monkeypox virus antigen was increased.
Immunogenicity of monkeypox virus mRNA vaccine
Antibody reaction
The researchers discovered that different doses (2ug/8ug) of mRNA vaccine caused more significant differences in serum binding antibody titers targeting A29 and A35 antigens than those targeting M1 and B6 antigens. In contrast, almost no IgG targeting four MPXV antigens was detected in the serum of mice given the smallpox vaccine MVA, indicating that the neutralization induced by the MVA vaccine may target a variety of antigenic determinants rather than specifically targeting A29/M1/A35/B6.
Next, the researchers found that vaccination of the tetravalent monkeypox mRNA vaccine triggered a strong Th1-dependent IgG2a response, low levels of IgG2b, IgG1, and IgG3 responses, accompanied by strong Fc-dependent effects, including antibody-dependent phagocytosis (ADCP), antibody-dependent neutrophil phagocytosis (ADNP), antibody-dependent cytotoxicity (ADCC), and antibody-dependent complement precipitation (ADCD). These data indicate that mRNA vaccines can trigger strong Th1-biased humoral immunity, accompanied by strong Fc receptor effects, which is significantly different from the humoral immunity triggered by the MVA smallpox vaccine.
Challenge test of the VACA vaccinia virus
The researchers immunized mice with the MVA smallpox vaccine and three different mRNA monkeypox vaccines (2 / 3 / 4). Three weeks later, the mice were intranasally vaccinated with the VACA cowpox virus (106 PFU).
The results indicated that the neutralizing antibody and binding antibody responses triggered by different doses of mRNA vaccine were different. For tetravalent vaccines, the specific binding antibody responses to A29L and A35R triggered by high- and low-dose mRNA vaccines were dose dependent; on the contrary, the antibody responses of M1 and B6 were strongly conserved in different doses of mRNA vaccines.
Compared with the attenuated vaccine MVA, the mRNA monkeypox vaccine can trigger a better neutralizing antibody response and inhibit the intercellular transmission of MPXV and VACV viruses, as well as induce a stronger humoral immune response biased towards Th1 targeting four antigens. MRNA monkeypox vaccine encoding a single MPXV antigen provides partial immune protection against the VACV virus, while mRNA monkeypox vaccine encoding a combination of 2, 3, or 4 MPXV antigens can prevent weight loss and death associated with monkeypox infection. With the combined effect of neutralizing and non-neutralizing antibodies, the cross-immune protection provided by the polyvalent monkeypox mRNA vaccine is better than that provided by the MVA smallpox vaccine.