Evaluation of the immune response to an mRNA vaccine prototype against COVID- 19: a preclinical study

Introduction: COVID-19 pandemic, highlighted the urgent need for rapid vaccine development.mRNA vaccines have proven to be a promising strategy due to their adaptability and ability to induce robust immune responses.This study evaluates the efficacy and immunophenotyping of an mRNA vaccine prototype under development against COVID-19.Objectives: To assess the potency and antigen expression efficiency of the mRNA vaccine prototype in HEK-293T cells; detect IFN--producing cells post-immunization; and antibody production. Methodology:In vitro potency assays were conducted using HEK-293T cells transfected with the vaccine prototype, naked mRNA, and a commercial mRNA vaccine for comparison.In vivo experiments used K18-hACE2 transgenic mice immunized with different doses of the prototype and a reference vaccine.Immune responses were evaluated through ELISPOT (IFN- secreting cells) and ELISA (total IgG antibody quantification).Results: Vaccine prototype demonstrated high antigen expression efficiency in HEK-293T cells, comparable to the reference vaccine.ELISPOT indicated a higher frequency of IFN- producing cells in response to the Spike protein, with the highest response in the prototype-immunized group (mean+/-SD: prototype: 758,6 vs commercial vaccine: 644,8).ELISA confirmed robust antibody responses, with elevated IgG titers in prototype-vaccinated groups (mean+/-SD: prototype: 3.559,69 vs commercial vaccine: 3.114,02). Conclusion:mRNA vaccine prototype has potent immune response, significant IFN- production and robust antibody responses.Compared to the reference vaccine, the prototype exhibited a superior immunological profile in some analyzed parameters.