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

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 an in-depth analysis of human bone marrow plasma cells. To do so, single cell transcriptomes and BCR sequencing of sorted plasma cells and memory B cells from 8 human bone marrow samples obtained from patients undergoing hip replacement surgery were prepared. In addition, cells were also incubated with DNA barcoded antibodies for Cellular Indexing of Transcriptomes and Epitopes by Sequencing (CITE-seq). When available, plasma cells and memory B cells from paired blood samples were likewise sorted and sequenced. Some bone marrow and blood 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 v2 (dual index) and Illumina NextSeq2000.