Study On The Correlation Between Human Peripheral Immune Cell Subsets Alteration And The Antibody Production After COVID-19 Vaccination

Background:The inactivated vaccine CoronaVac（Sinovac Biotech）is among the mostly used COVID-19 vaccine globally.Unlike the fully researches of humoral and cellular responses of m RNA vaccine platform,how would CoronaVac vaccine-induced immune response evolve longitudinally and how a third CoronaVac dose affected the magnitude and quality of immune responses,particularly against the highly divergent variant Omicron remain elusive.Human immune system is broadly divided into the adaptive immune system and innate immune system.The adaptive immune responses are important for the control and clearance of almost all viral infections,and consist of three cell types:B cells（the source of antibodies）,CD4⁺T cells and CD8⁺T cells.Natural killer（NK）cells,as the first-line responder against viral infection,played an important role in the innate immune responses.The longitudinal study of humoral and cellular immune responses induced by CoronaVac vaccine is helpful to understand the effectiveness and durability following inactivated vaccine administration.Objective:The purpose of this study was to evaluate the alterations of adaptive immune cells such as polyclonal and SARS-CoV-2 spike-specific CD4⁺T cell subsets,CD8⁺T cells,and the major innate immune cell,NK cell subsets following three doses of CoronaVac.The correlation between immune cell subsets and SARS-CoV-2-specific Ig G,Ig M,Ig A and neutralizing antibody production.Methods:88 healthy volunteers who received 2-3 doses of homologous inactivated CoronaVac vaccine at Affiliated Hospital of Jiangnan University and The Fifth People’s Hospital of Wuxi from December 2020 to December 2021 were recruited.Their basic information were collected.Peripheral blood was collected and peripheral blood mononuclear cells and serum were isolated at five time points.The magnetism particulate chemistry luminescence method was utilized to detect the plasma SARS-CoV-2 specific Ig G,Ig M,Ig A and neutralizing antibody titers.Pseudovirus neutralization assay was applied to calculate the serum neutralization activity against SARS-CoV-2 WT（wild-type）,Omicron B.1.1.529,BA.2,BA.4/BA.5 and BA.2.75.2 variants.Spectral flow cytometry was used to detect the frequencies of peripheral circulating polyclonal and antigen-specific CD4⁺T cell subsets,CD8⁺T cells and NK cells,and the expression of their surface markers.The correlation between the frequency of follicular helper T cells and antibodies was analyzed.Results:Compared with pre-vaccination baseline,both the second and third dose of CoronaVac induced robust SARS-CoV-2 specific Ig G and neutralizing antibodies,with a third vaccine further increased the overall magnitude of antibody response,and neutralization against Omicron sub-lineages B.1.1.529,BA.2,BA.4/BA.5 and BA.2.75.2.The frequencies of polyclonal T_H1 and c T_FH cells increased significantly after the second vaccination compared with baseline.The frequencies of polyclonal c T_FH1 and c T_FH-EM were significantly increased after the second and third vaccine administration,and the effector-memory like c T_FH1 cells(c T_FH1-EM)were particularly sensitive to antigens.Spike-specific CD4⁺T cell and c T_FH cells were markedly increased by the second and third dose of CoronaVac vaccine,accompanied with altered composition of functional c T_FH cell subsets with distinct effector and memory potential.Additionally,c T_FH cells are positively correlated with neutralizing antibody titers.Both polyclonal and antigen-specific CXCR3⁺CXCR5⁺CD8⁺T cells increased strikingly by the second and third vaccine dose.And the antigen-specific CXCR3⁺CXCR5⁺CD8⁺T cells persist at least 6 months post the second dose of vaccination.Moreover,the frequency of polyclonal CD56^dimCD16^dim NK cells increased after each dose of vaccination,and activated CD56^dimCD16^dim/bright NK cells stimulated by antigen reached a peak after the third vaccine dose.Conclusion:Three doses of CoronaVac vaccine could induce robust antibody responses,spike-specific CD4⁺T cell responses,CD8⁺T cell responses and innate immune responses.CoronaVac vaccine-induced spike-specific T cells T_FH cells are capable of supporting humoral immunity for long-term immune protection.