Human T follicular helper clones seed the germinal center-resident regulatory pool

Abstract How FOXP3 + T follicular regulatory (Tfr) cells simultaneously steer antibody formation toward microbe/vaccine recognition and away from self-reactivity remains unsettled. To explore human Tfr cell provenance, function and location heterogeneity, we used paired TCRVA / TCRVB sequencing to distinguish tonsillar Tfr cells clonally related to natural Tregs (nTfr) from those likely induced from Tfh cells (iTfr). The proteins iTfr and nTfr cells differentially expressed were utilized to pinpoint their in situ locations via multi-plex microscopy and establish divergent functional roles. In-silico and tonsil organoid tracking models corroborated the existence of separate Treg-to-nTfr and Tfh-to-iTfr developmental trajectories. In total, we have identified human iTfr cells as a distinct CD38-expressing, GC-resident, Tfh-descended subset that gains suppressive function while retaining capacities for B-cell help whereas CD38 - nTfr cells are elite suppressors primarily localized to follicular mantles. Interventions differentially targeting Tfr subsets may provide therapeutic opportunities to boost immunity or more precisely treat autoimmune diseases. One sentence summary Human tonsillar Tfr clones descend from either Treg or Tfh lineages and provenance predicts their TCR repertoires, locations and functional characteristics.