Abstract
Background: Monitoring cellular immune responses elicited in vaccinated individuals is highly complicated. Methods: 28 individuals participated during the vaccination process with 12 BNT162b2 mRNA (Pfizer) vaccine. Specific anti-RBD IgG using a classic ELISA was performed in days 10 and 20 (after one dose of the vaccine) and on day 35 (after two vaccine doses) in serum samples of all participants. In parallel, DTH (delayed-type hypersensitivity) Skin Test using S protein was performed before (11/28) and after two doses (28/28) of the vaccine. Results: 6/28 individuals were considered positive for the specific anti-RBD IgG positive at day 10, whereas all 28 individuals were positive at day 20. Moreover, 28/28 individuals increased the OD ratios at day 36 (2 doses). DTH cutaneous test was performed on 11/28 participants at day 20 (1 dose) showing 8/11 a positive reaction at 12 h. DTH of all participants was performed on day 36 (2 doses), showing 28/28 positive reactions at 12 h. Conclusion: This report describes the first publication of the results obtained using an in vivo method, the classical DTH response to the Spike protein to assess T-cell immune responses in vaccinated individuals. This affordable and simple test would help to answer basic immunogenicity questions on large-scale population vaccine studies.
Highlights
Ongoing studies are monitoring immune responses elicited by mRNA vaccines
This report describes the first publication of the results obtained using an in vivo method, the classical delayed-type hypersensitivity (DTH) response to the Spike protein to assess T-cell immune responses in vaccinated individuals
Six out of 28 sera collected at day 10 showed specific anti-receptor binding domain (RBD) IgG Optical Density (OD) ratio values considered positive (>0.8), whereas serum from each of 28 individuals were positive at day 20 (1 dose)
Summary
Ongoing studies are monitoring immune responses elicited by mRNA vaccines. Few studies have been focused on the role that the immune cellular responses might play in the development of immunity to SARS-CoV-2 and what are the implications for vaccines.Usually, most studies have systematically explored only humoral responses assuming that individuals with high antibody levels after infection should have a high number of SARS-CoV-2 specific T cells. Few studies have been focused on the role that the immune cellular responses might play in the development of immunity to SARS-CoV-2 and what are the implications for vaccines. A preprint of a recent study of 100 people with a history of asymptomatic or mild COVID-19 reports T cell mediated immune responses lasting for at least six months in all participants [2]. Most of these studies have been mainly focused on the humoral side with few studies addressing cellular immune responses [3,4,5]. One of the reasons behind this lack of studies is that both ELISAs antibody methods and in vitro cellular assays require the extraction of a blood sample from the patient that complicate massive analysis in large populations
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