Tracking memory T follicular helper cells in the draining lymph node following boost vaccination in humans 2257551

Abstract Introduction T follicular helper (Tfh) cells are crucial in germinal center (GC) reactions, supporting B-cell maturation and long-term antibody production. While Tfh dynamics during primary and secondary immune responses are well-studied in mice, little is known about human Tfh behavior in draining lymph nodes after repeat vaccination. Recent advances, such as serial fine-needle aspiration (FNA) of lymph nodes, now make it possible to monitor these responses in humans. The present study aimed to track and characterize human spike-specific Tfh cells in the draining lymph node following SARS-CoV-2 mRNA booster vaccination, and to compare these memory responses to the primary vaccination phase. Methods We conducted serial lymph node FNAs in healthy immunologically naïve adults receiving primary and booster mRNA COVID-19 vaccines (1 year apart). We used single-cell RNA sequencing with paired T cell receptor (TCR) sequencing to analyze spike-specific Tfh clonotypes and transcriptional profiles. Results We show that the post-boost Tfh response was dominated by spike-specific TCR clonotypes already present after the primary vaccination, indicating robust memory recall. A minority of novel spike-specific Tfh clones emerged after boosting, suggesting limited recruitment of new Tfh populations during the secondary germinal center reaction. Secondary germinal center Tfh cells differed markedly from primary Tfh cells: 1) they exhibited a higher frequency of IL-10+ Tfh cells; 2) they had fewer classical germinal center Tfh (with high CXCR5 and PDCD1); and 3) boost-induced Tfh cells showed upregulation of transcription factors such as RUNX3, RUNX1, KLF2, and NFKB1, reflecting a memory-specific transcriptional signature. Conclusion Overall, our data shows that booster vaccination triggers a phenotypically and transcriptionally unique memory Tfh response in human lymph nodes, emphasizing that immune recall involves reactivation of existing memory clones to shape long-term humoral immunity. Funding Source R01AI173203 Topic Categories Immune Mechanisms of Human Disease (HUM)