W151 - Analysis of T Cell Response Induced by a Fifth Dose of Inactivated SARS-CoV-2 Vaccines Based on the Omicron Variant or on a Trivalent Vaccine Containing the Ancestral, Delta and Omicron Variants by Multiparametric Flow Cytometry

Antonia Reyes – Pontificia Universidad Catolica de Chile; Cristian Gutierrez – Universidad de Chile; Francisca Roman – Pontificia Universidad Catolica de Chile; Linmar Rodriguez – Pontificia Universidad Catolica de Chile; Constanza Mendez – Pontificia Universidad Catolica de Chile; Daniela Moreno – Pontificia Universidad Catolica de Chile; Mariana Rios – Pontificia Universidad Catolica de Chile; Alex Cabrera – Pontificia Universidad Catolica de Chile; Pablo Gonzalez – Pontificia Universidad Catolica de Chile; Leandro Carreno – Universidad de Chile; Alexis Kalergis – Pontificia Universidad Catolica de Chile; susan Bueno – Pontificia Universidad Catolica de Chile

Abstract Text: The COVID-19 pandemic pushed the rapid development of vaccines to protect the population from severe disease and death caused by SARS-CoV-2. We previously showed that four doses of CoronaVac®, a SARS-CoV-2 inactivated vaccine, induce the activation of Spike (S) specific CD4+CD137+OX40+ T cells.
Here, we studied the effect in CD4+ and CD8+ T cell activation in subjects vaccinated with a fifth dose of an inactivated vaccine based on the Omicron BA.1 variant or a trivalent vaccine based on the Wuhan, Delta and Omicron BA.1 variants.
Peripheral blood mononuclear cells were collected from 6 subjects before and after immunization (28 days), and stimulated with a megapool (MPs) of peptides derived from the S protein of the ancestral virus (WT), the Delta and the Omicron (BA.1 and BA.2) variants. Activated CD3+ T cells were visualized by Barnes-hut distributed Stochastic Neighbor Embedding (bh-SNE) and clustered through the EMGM algorithm.
CD3+ T cells were grouped in 24 clusters, where 3 clusters showed changes in their frequency after vaccination. C17 (activated fully differentiated CD4+ memory T cells) increased its frequency following stimulation with WT-MP-S. C21 (CD8+ central memory T cells) reduced its frequency when stimulated with WT-MP-S and BA.2-MP-S. Finally, C24 (effector CD8+ memory T cells), decreased following stimulation with WT-MP-S.

The cellular response induced by a fifth dose of SARS-CoV-2 vaccine is complex and not restricted to the induction of CD4+CD137+OX40+ T cells. We speculate that additional functional markers will improve our ability to evaluate the effects of SARS-CoV-2 boosters in T cell function.