Ishigaki, H. | Search bioRxiv

bioRxiv2021

Optimization of an LNP-mRNA vaccine candidate targeting SARS-CoV-2 receptor-binding domain

In 2020, two mRNA-based vaccines, encoding the full length of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike protein, have been introduced for control of the coronavirus disease (COVID-19) pandemic1,2. However, reactogenicity, such as fever, caused by innate immune responses to the vaccine formulation remains to be improved. Here, we optimized a lipid nanoparticle (LNP)-based mRNA vaccine candidate, encoding the SARS-CoV-2 spike protein receptor-binding domain (LNP-mRNA-RBD), which showed improved immunogenicity by removing reactogenic materials from the vaccine formulation and protective potential against SARS-CoV-2 infection in cynomolgus macaques. LNP-mRNA-RBD induced robust antigen-specific B cells and follicular helper T cells in the BALB/c strain but not in the C57BL/6 strain; the two strains have contrasting abilities to induce type I interferon production by dendritic cells. Removal of reactogenic materials from original synthesized mRNA by HPLC reduced type I interferon (IFN) production by dendritic cells, which improved immunogenicity. Immunization of cynomolgus macaques with an LNP encapsulating HPLC-purified mRNA induced robust anti-RBD IgG in the plasma and in various mucosal areas, including airways, thereby conferring protection against SARS-CoV-2 infection. Therefore, fine-tuning the balance between the immunogenic and reactogenic activity of mRNA-based vaccine formulations may offer safer and more efficacious outcomes.

immunology↗

bioRxiv2020

Neutralizing antibody-dependent and -independent immune responses against SARS-CoV-2 in cynomolgus macaques

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infectious disease (COVID-19) has been threatening the world because of severe symptoms and relatively high mortality. To develop vaccines and antiviral drugs for COVID-19, an animal model of SARS-CoV-2 infection is required to evaluate the efficacy of prophylactics and therapeutics in vivo. Therefore, we examined the pathogenicity of SARS-CoV-2 in cynomolgus macaques until 28 days after virus inoculation in the present study. Cynomolgus macaques showed body temperature rises after infection and X-ray radiographic viral pneumonia was observed in one of three macaques. However, none of the macaques showed life-threatening clinical signs of disease corresponding that approximately 80% of human patients did not show a critical disease in COVID-19. A neutralizing antibody against SARS-CoV-2 and T-lymphocytes that produced interferon (IFN)-{gamma} and interleukin (IL)-2 specifically for SARS-CoV-2 N protein were detected on day 14 in the macaque that showed viral pneumonia. On the other hand, in the other macaques, in which a neutralizing antibody was not detected, T-lymphocytes that produced IFN-{gamma} specifically for SARS-CoV-2 N protein increased on day 7 to day 14 prior to an increase in the number of T-lymphocytes that produced IL-2. These results suggest that not only a neutralizing antibody but also cellular immunity augmented by IFN-{gamma} has a role in the elimination of SARS-CoV-2. Thus, because of the mild clinical signs of disease and low/no antibody responses against SARS-CoV-2 in two thirds of the macaques, cynomolgus macaques are appropriate to extrapolate human responses in vaccine and drug development. Author SummarySevere acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infectious disease (COVID-19) has been threatening the world. To develop vaccines and antiviral drugs for COVID-19, an animal model of SARS-CoV-2 infection is required to evaluate their efficacy in vivo. Therefore, we examined the pathogenicity of SARS-CoV-2 in a non-human primate model until 28 days after virus inoculation. Cynomolgus macaques showed a fever after infection and X-ray radiographic viral pneumonia was observed in one of three macaques. However, none of the macaques showed life-threatening symptoms. A neutralizing antibody against SARS-CoV-2 and T-lymphocytes that produced interferon (IFN)-{gamma} and interleukin (IL)-2 specifically for SARS-CoV-2 protein were detected on day 14 in the macaque that showed viral pneumonia. In the other macaques, in which a neutralizing antibody was not detected, T-lymphocytes that produced IFN-{gamma} specifically for SARS-CoV-2 N protein increased on day 7 to day 14. These results suggest that not only a neutralizing antibody but also cellular immunity augmented by IFN-{gamma} has a role in the elimination of SARS-CoV-2. Thus, because of the mild symptoms and low/no antibody responses against SARS-CoV-2 in two thirds of the macaques, cynomolgus macaques are appropriate to extrapolate human responses in vaccine and drug development.

microbiology↗