Role of gamma irradiation and disaccharide trehalose to induce immune responses in Syrian hamster model against Iranian SARS-CoV-2 virus isolate

Abstract

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus is the causative agent of the emerging zoonotic respiratory disease. One of the most important prerequisites for combating emerging diseases is the development of vaccines within a short period of time. In this study, antigen-irradiated, inactivated SARS-CoV-2 viruses and the disaccharide trehalose were used to enhance immune responses in the Syrian hamster. The SARS-CoV-2 virus was isolated from tracheal swabs, confirmed by real-time polymerase chain reaction, and propagated on Vero cells. For inactivation, it was irradiated with 14.00 kGy gamma radiation. Evaluation of the antigenic properties of the spike protein subunit S1 showed that the antigens were intact after gamma irradiation. The gamma-irradiated and formalin-treated viruses were used to immunize hamsters in four vaccine formulations. Neutralizing antibodies increased significantly in all vaccinated groups three weeks after the second and third vaccinations. The concentration of secretory immunoglobulin A in the irradiated vaccine plus trehalose increased significantly in nasal lavage and nasopharyngeal-associated lymphoid tissue fluids three weeks after the second and third vaccinations. The lymphocyte proliferation test in the spleen showed a significant increase in all vaccinated hamsters, but the increase was greater in irradiated vaccine plus trehalose and irradiated vaccine plus alum. We can recommend the irradiated inactivated vaccine SARS-CoV-2 plus trehalose (intra-nasal) and another irradiated inactivated vaccine SARS-CoV-2 plus alum (subcutaneous) as safe vaccines against coronavirus disease of 2019 (COVID-19), which can stimulate mucosal, humeral, and cellular immunities. However, the protectivity of the vaccine against COVID-19 in vaccinated hamsters must be investigated in a challenge test to assess the potency and efficiency of vaccine.

Keywords: Gamma irradiation; Immune response; Inactivated vaccine; Mucosal immunity; SARS-CoV-2 virus.

Fig. 1

Dose-response curve of gamma irradiated severe acute respiratory syndrome coronavirus 2 virus samples. TCID₅₀: 50.00% tissue culture infectious dose.

Fig. 2

A) The inhibition percent of the spike-angiotensin-converting enzyme 2 (ACE2) binding, indicating the neutralizing antibody titration; B) IgA concentration (µg mL^-1); and C) The spleen lymphocyte proliferation results being showed as stimulation index. PI: Pre-immune; I.V: Irradiated vaccine; I.V.T: Irradiated vaccine plus trehalose; F.V.A: Formalin inactivated vaccine plus alum; I.V.A: Irradiated vaccine plus alum; IN: Intra-nasal, SC: Subcutaneous; NC: Negative control; PBS: Phosphate-buffered saline; wa1v: Weeks after first vaccination; wa2v: Weeks after second vaccination; and wa3v: Weeks after third vaccination. *: p < 0.05.