Pre-existing T cell immunity determines the frequency and magnitude of cellular immune response to two doses of mRNA vaccine against SARS-CoV-2

Little is known about the factors associated with lack of T-cell response to mRNA vaccines against SARSCoV-2. In a prospective cohort of 61 health care workers (HCWs), 21% and 16% after the first dose of mRNA BNT162b vaccine, and 12% and 7% after the second dose, showed lack of CD4+ and CD8+ T-cell response, respectively. Pre-existing T-cell immunity, due to past infection (46%) or cross-reactive cellular response (26%), was significantly associated with T-cell response in frequency (CD4+ T-cell, 100% vs 82% after two doses; p = 0.049) and in the magnitude of T-cell response during follow up. Furthermore, baseline CD4+ T-cell correlated positively with the titer of specific IgG-antibodies after first and second vaccine dose. Our data demonstrate that cross-reactive T-cells correlate with a better cellular response as well as an enhanced humoral response, and we confirm the close correlation of humoral and cellular response after mRNA vaccination.(c) 2022 The Author(s). Published by Elsevier Ltd.

Automated summary

Little is known about the factors associated with the lack of T-cell response to mRNA vaccines against SARS-CoV-2. A study on a cohort of 61 healthcare workers found that 21% and 16% showed a lack of CD4+ and CD8+ T-cell response after the first dose of the mRNA BNT162b vaccine, and 12% and 7% showed a lack of response after the second dose, respectively. Pre-existing T-cell immunity, either from past infection or cross-reactive cellular response, was significantly associated with T-cell response frequency and magnitude. Baseline CD4+ T-cell levels correlated positively with the titer of specific IgG antibodies. These findings suggest that cross-reactive T-cells are linked to better cellular and humoral responses after mRNA vaccination.