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Severa, E.

Publications and source records attributed to Severa, E..

2 recordsLinked to original sources
bioRxiv2026

Tfh dysfunction underlies poor responses to HBV vaccination

The primary goal of vaccination is to induce durable protection through generation of antigen-specific humoral immunity and cellular immune memory. Yet the same vaccine may elicit durable protection in some and less durable responses in others. Antigen-specific antibody responses arise from germinal centers (GCs), where T follicular helper (Tfh) cells help cognate B cells undergo somatic hypermutation (SHM), affinity maturation to generate humoral protection and cellular immune memory. In humans, however, the mechanisms linking GC dynamics to downstream antibody output remain incompletely characterized. To identify the molecular and cellular events that underlie differential vaccine responsiveness, we leveraged the known, pronounced variability in vaccine antigen-specific antibody concentration and durability observed after Hepatitis B virus (HBV) immunization. We longitudinally profiled 101 healthy adults undergoing either de novo (n=59) or booster (n=42) immunization. We then stratified participants into High (>100 mIU/mL) and Low (<100 mIU/mL) responder groups based on vaccine antigen-specific antibody responses. From this cohort, we obtained core needle biopsies (CNBx) of vaccine-draining lymph nodes from 10 participants (High Responder n=6, Low Responder n=4), 10-21 days post-final vaccination and performed single-cell RNA sequencing with paired antigen receptor sequencing. Lymph node BCR repertoire analysis revealed convergent, semi-public clonotypes across unrelated participants with elevated SHM. Transcriptomic profiling of GC-B cells uncovered stark functional divergence between response groups, with High Responders showing robust activation across both dark zone (DZ) and light zone (LZ) compartments and enrichment of MYC and mTORC1 signaling. In contrast, Low Responders exhibited a contracted LZ compartment and a stalled GC B cell response. This divergence in B cell responses corresponded to changes in the T cell compartment. High Responders harbored an expanded Tfh subset marked by increased expression of CXCL13, ICOS, and GNG4, indicative of their GC localization and capacity to provide B cell help. Moreover, receptor-ligand analysis indicated that these GNG4+Tfh formed coordinated costimulatory networks capable of driving LZ GC-B cell licensing. Low Responders demonstrated a divergent program in which their GNG4+Tfh displayed aberrant inflammatory transcriptional activity. This inflammatory signaling was associated with reduced specificity of BCL6 regulon activity despite maintained expression of canonical Tfh genes. Together, these findings reveal that variable HBV vaccine responsiveness was associated with transcriptional network alterations in the GNG4+Tfh subset, offering a molecular framework for understanding poor vaccine responses. One Sentence SummaryLymph node Tfh dysfunction is associated with poor vaccine responses to Hepatitis B virus vaccination

immunology↗
bioRxiv2025

Coordinated circulating and tissue-based T cell responses precede xenograft rejection

Despite the life-saving successes of solid organ transplantation, the number of individuals needing organ transplant far exceeds the number of organs available for use each year. Porcine xenotransplantation, or the use of pig organs for transplantation in people, holds substantial promise but xenograft rejection in humans is poorly understood. T cell rejection by the host immune system is a major challenge for human allografts and may limit the longevity of porcine xenografts. To study the xenograft rejection, we evaluated T cell responses and repertoire dynamics across tissues following porcine thymokidney transplantation in a decedent model over 61 days after bilateral native kidney nephrectomy. Despite induction with anti-thymocyte globulin and ongoing immune suppression consisting of rituximab, corticosteroids, calcineurin inhibition, and mycophenolate mofetil, human T cell infiltration of the xenograft was observed and was associated with xenograft dysfunction. Longitudinal analysis of T cell clonotypes in biopsies of thymokidney revealed accumulation of clonal human CD4 and CD8 T cell responses. Moreover, circulating activated T cells, including circulating T follicular helper (cTfh), were xeno-reactive and increased in frequency around rejection events. We confirmed clonal dominance of a single CD8 clonotype - identified as donor-reactive in a mixed lymphocyte reaction - in the circulation leading up to the acute cellular rejection event. Following re-treatment with anti-thymocyte globulin and intensification of corticosteroids, the T cell clonotypes were dramatically diminished in frequency in thymokidney and lymph nodes, though not eliminated. Over time of observation, the T cell clonotypes were shared across multiple compartments, including xenograft, circulation and lymph nodes and formed clonal families with known xeno-reactive clonotypes, suggesting a coordinated immune response against a limited pool of antigenic targets. Together, these data demonstrate T cell repertoire dynamics across tissues in the setting of xenograft rejection and highlight opportunities for early surveillance, prediction and potential intervention. One-sentence summaryAfter pig-to-human kidney xenotransplantation, xenoreactive T cells form clonotypic families across blood, graft, and lymphoid tissues, indicating a coordinated and targeted response.

immunology↗