Recruitment of plasma cells from follicular and extrafollicular immune reactions to the bone marrow I

Bone marrow plasma cells (BMPC) are the correlate of humoral immunity, consistently releasing antibodies into the bloodstream. It remains unclear if BMPC reflect different activation environments or maturation of their precursors. Here we define human BMPC heterogeneity and track the recruitment of antibody-secreting cells (ASC) from SARS-CoV-2 vaccine immune reactions to the bone marrow (BM). Trajectories based on single-cell transcriptomes and repertoires of peripheral and BM ASC reveal sequential colonisation of BMPC compartments. In activated B cells, IL-21 suppresses CD19 expression, indicating that CD19low-BMPC are derived from follicular, while CD19high-BMPC originate from extrafollicular immune reactions. In primary immune reactions, both CD19low- and CD19high-BMPC compartments are populated. In secondary immune reactions, most BMPC are recruited to CD19high-BMPC compartments, reflecting their origin from extrafollicular reactivations of memory B cells. A pattern also observed in vaccinated-convalescent individuals and upon diphtheria/tetanus/pertussis recall-vaccination. Thus, BMPC diversity reflects the evolution of a given humoral immune response. This experiment was designed for a longitudinal study of peripheral blood plasmablasts upon vaccination with different vaccines and vaccination schemes. To do so, single cell transcriptomes and BCR/TCR sequencing of sorted plasmablasts, memory B cells and activated T cells from peripheral blood samples of 36 individuals taken at different time points after first, second or third dose of COVID-19 (Comirnaty or Vaxzevria) or dipheteria/tetanus/pertussis vaccines were prepared. In addition, cells were also incubated with DNA barcoded antibodies for Cellular Indexing of Transcriptomes and Epitopes by Sequencing (CITE-seq). Some samples were additionally incubated with fluorophore-coupled tetanus toxoid and SARS-CoV-2 Spike Protein tetramers for antigen-specific cell sorting and sequencing. Sequencing was performed using the 10X Genomics platform with the Single Cell 5’ Library & Gel Bead Kit v1.1 (single index) and Illumina NextSeq2000.