Tu175 - Characterization of the T Cell Responses Elicited by Four Doses of an Inactivated sars-cov-2 Vaccine in Adults

Constanza Mendez – Millennium Institute on Immunology and Immunotherapy, Pontificia Universidad Católica de Chile; Hernan Peñaloza – Millennium Institute on Immunology and Immunotherapy, Pontificia Universidad Católica de Chile; Felipe Melo-Gonzalez – Millennium Institute on Immunology and Immunotherapy, Universidad Andrés Bello; Mariana Rios – Millennium Institute on Immunology and Immunotherapy, Pontificia Universidad Católica de Chile; Luisa Duarte – Millennium Institute on Immunology and Immunotherapy, Universidad Andrés Bello; Alex Cabrera – Pontificia Universidad Católica de Chile; Cristian Gutierrez – Universidad de Chile; Alba Grifoni – La Jolla Institute for Immunology (LJI); Alessandro Sette – La Jolla Institute for Immunology (LJI); Daniela Weiskopf – La Jolla Institute for Immunology (LJI); CoronaVac03CL Study group; Jorge Soto – Millennium Institute on Immunology and Immunotherapy, Universidad Andrés Bello; Leandro Carreño – Universidad de Chile; Pablo Gonzalez – Millennium Institute on Immunology and Immunotherapy, Pontificia Universidad Católica de Chile; Alexis Kalergis – Millennium Institute on Immunology and Immunotherapy, Pontificia Universidad Católica de Chile

Abstract Text: Background. The SARS-CoV-2 Omicron variant has challenged the control of the COVID-19 pandemic even in highly vaccinated countries due to its ability to partially evade the immune response induced by vaccines. Here we studied whether a second booster of CoronaVac®, an inactivated vaccine, enhances the cellular response against the ancestral SARS-CoV-2 and the Omicron variant.
Methods. In the context of a phase 3 clinical study, SARS-CoV-2 cellular immunity was analyzed in stimulated peripheral mononuclear cells of 46 volunteers by flow cytometry and ELISPOT.
Findings. We observed a significant increase of CD4+ T cell expressing activate inducing markers (AIM+) and IFN-gamma producing cells after stimulation with a pool of peptides derived from the Spike protein at 2 and 4 weeks after the second dose of CoronaVac. We observed that the response remained stable after first and the second booster dose and no significant differences in IFN-gamma secreting cells or AIM+CD4+ T cells were observed. Importantly, CD4+ T cell response was equally increased when stimulation with a pool of peptides derived from the Spike protein from the Omicron variant. Furthermore, we observed an increase in the number of responder individuals at 4 weeks after the second booster.
Interpretation. A second booster of CoronaVac® contributes to stabilizing spike-specific CD4+ T cell responses against the ancestral SARS-CoV-2 strain and the Omicron variant.