# Cellular Immunological Memory T Cells and IL15RA Gene Polymorphism in COVID-19 Vaccinated Individuals from Southern Brazil

## TL;DR

This study examines memory T cells and a genetic variant in vaccinated individuals from southern Brazil to understand immune responses and vaccine effectiveness.

## Contribution

The study explores the impact of IL15RA gene polymorphism on T cell memory in vaccinated individuals, revealing genotype-specific immune responses.

## Key findings

- A decrease in memory T cell subsets was observed in response to SARS-CoV-2 stimuli.
- Participants with the TT genotype showed increased CD8+ and CD4+ T cell subsets after specific vaccination regimens.
- Booster doses are suggested to maintain cellular immune protection against emerging variants.

## Abstract

Background: The development of safe and effective vaccines against SARS-CoV-2 was crucial for controlling COVID-19 and establishing long-lasting immune memory in the population. Methods: This study evaluated cellular immune memory in individuals vaccinated with different regimens in Rio Grande do Sul using flow cytometry. Additionally, the rs2228059 polymorphism in the IL15RA gene was genotyped. A total of 62 participants were randomly recruited. Results: A decrease in memory T cell subsets in response to SARS-CoV-2 stimuli was observed in total CD3+, CD4+, and CD8+ T cells. Regarding the timing of the last vaccine dose, 94.4% of participants had received their final COVID-19 vaccination at least two years prior to recruitment. The rs2228059 polymorphism was genotyped in 443 individuals from the Rio Grande do Sul population. Among participants who received the ChAdOx1/ChAdOx1/BNT162b2 vaccination regimen and carried the TT genotype, an increase in CD8+ naive, CD8+ effector and CD4+ naive subsets was observed in stimulated cells. Although preliminary, the results suggest no major differences between vaccination regimens. Conclusions: The progressive reduction in memory T cell counts supports the need for booster doses, which is essential not only in the context of new emerging variants but also especially to maintain adequate cellular immune protection.