Natural and hybrid immunity: A comparative study of T cell response against SARS-CoV-2

Following SARS-CoV-2 infection, COVID-19 vaccination remains prudent as a form of combined protection. This strategy fosters the development of a hybrid immune response in individuals, surpassing the protective efficacy of natural infection or just vaccination. However, many questions remain unsolved, and more studies are needed to understand this type of immunity. Considering this, this study aimed to compare the T-cell immune profile of unvaccinated and vaccinated patients who had previously recovered from mild COVID-19. In a quiescent state characterized, CD8 + T cells derived from individuals who had experienced mild COVID-19 and remained unvaccinated exhibited elevated expression of CD69 and IFN-γ compared to the group that received the vaccination. Conversely, within the CD4 + T cell population, greater levels of IFN-γ, TNF-α, CD107a, and perforin are observed in the unvaccinated group compared to those vaccinated. Furthermore, a distinct functional profile emerges in T cells obtained from COVID-19-vaccinated patients who experienced mild COVID-19. Upon exposure to spike antigens, CD4 + T cells demonstrate heightened activity and functionality. This is evidenced by the augmented expression of CD137, CD69, and IL-10 compared to similarly affected yet unvaccinated patients. Moreover, the CD8 + T cell subset within the vaccinated cohort displays heightened levels of perforin, TNF-α, and IL-10 when juxtaposed with the unvaccinated group. These findings collectively imply the ability of unvaccinated individuals to develop an effector-oriented profile in their immune responses. Conversely, individuals who have encountered mild COVID-19 and subsequently received vaccination can orchestrate a proficient antiviral immune response, coupled with a major immunoregulatory capacity.