CD4⁺ T Cell Dysregulation in Long COVID: Insights from an Unvaccinated Cohort

We analyzed a Brazilian cohort of patients recruited between September 2020 and February 2021, during the first wave of the pandemic (Wuhan-Hu-1 variant), comprising mostly unvaccinated individuals. We assessed humoral responses to SARS-CoV-2 and latent viruses in 104 patients. Additionally, we investigated the immune signatures of CD4+ T cells in a subset of 6 LC and 4 recovered control (RC) unvaccinated patients, recruited 1 to 2 months after symptom onset, utilizing a combination of flow cytometry and single-cell RNA sequencing.

Results: Systemic humoral responses to SARS-CoV-2 and reactivated latent viruses were comparable between the LC and RC groups, as were the overall distributions of CD4+ T cell subsets. However, single-cell RNA sequencing revealed distinct immune signatures. Antigen-responsive CD4+ T cells in LC patients demonstrated a signature of acute activation, characterized by the upregulation of genes such as CD38 and interferon-stimulated genes, including IFITM1.

Furthermore, gene set enrichment analysis indicated that LC patients exhibit increased expression of interferon-alpha/gamma signatures compared to RC. Analysis of the T cell receptor repertoire presented no evidence of clonal expansion. Discussion: Our findings imply that LC immunopathology is driven by a qualitative T cell dysfunction characterized by CD4+ non-proliferative activation more than one month after symptom onset.

This pattern is consistent with persistent antigen stimuli, though the underlying mechanism and its therapeutic implications require further investigation