Defining origins of malignant B cells: a new circulating normal human IgM+D+ B-cell subset lacking CD27 expression and displaying somatically mutated IGHV genes as a relevant memory population

Abstract

In probing the cell of origin in malignant B cells, an imprint of somatic hypermutation (SHM) in immunoglobulin (Ig) variable (V) region genes delineates antigen encounter, and identifying the precise pathway generating SHM in the normal B-cell counterpart becomes relevant. SHM remains the definitive memory imprint in normal human B cells, but CD27 expression also delineates memory. Recently, dye extrusion adenosine triphosphate-binding transporter assays identified circulating isotype-switched memory B cells that lacked CD27, yet exhibited low levels of SHM. To extend findings, we report a pre-switched CD27 Àve circulating memory B-cell population in normal blood using comparable assays, and isolated CD19 þ IgM þ D þ CD27 Àve cells (499% purity) for the analysis of IGHV5/IGHV3-IGHM transcripts. Of these (n ¼ 334), B78% were germ line and naive B cell derived. Strikingly, 21.9% of the transcripts were mutated. They showed 3-5 mutations (13.5% of sequences) and 45 mutations (8.4% of sequences) per transcript. Accrual of mutations in a subset of CD19 þ IgM þ D þ CD27 Àve cells define a new circulating pre-switched memory B-cell pool, present in substantial numbers in the population harboring naive B cells. These CD19 þ IgM þ D þ CD27 Àve memory B cells may have a distinct lineage and function, and seem relevant to understanding origins of malignant B cells, in particular those of hairy cell leukemia cells, which display mutated V genes yet lack CD27 expression.

TLR9 Ligand (CpG Oligodeoxynucleotide) Induces CLL B-Cells to Differentiate into CD20+ Antibody-Secreting Cells

“…Thus, the differences in mutational status between CLL cells would be unsurprising if (i) unmutated CLL B-cells are derived from less “antigen-experienced” IgM memory B-cells with little or no SHM [accounting for around 10% of IgM memory B-cells (9, 13)], and (ii) mutated CLL B-cells are derived from well “antigen-experienced” IgM memory B-cells with a high SHM frequency. It is noteworthy that human IgM memory B-cells have a heterogeneous phenotype and include both a CD5 + CD27 + subpopulation (6) and a mutated CD27 − subpopulation (58). Taken as whole, our observations suggest that IgM memory B-cells might well be the normal counterpart of CLL B-cells.…”

Hairy cell leukemia cell lines expressing annexin A1 and displaying B-cell receptor signals characteristic of primary tumor cells lack the signature BRAF mutation to reveal unrepresentative origins

“…14 The dual aspect of mutated IGHV genes yet absence of CD27 expression, the classical marker for normal germinal center-derived memory B cells, has raised the question of an unusual cell of origin in HCL, for which our recent report of normal IgM þ B cells that lack CD27 and carry a low level of mutations in IGHV genes may be relevant. 26 We also examined BCR function in tumor cells selected by CD19, CD11c Hi and CD103 expression, using anti-surface Table 1), ANXA1 expression ( þ to þ þ þ þ by densitometry of western blots), sIg ( þ to þ þ þ denotes % cells positive) and Ca 2 þ flux induced by anti-sIg stimuli ( þ to þ þ þ þ denotes % cells responding over threshold), together with IGHV gene use (ND is not done). Letter to the Editor and after anti-sIg stimulation.…”

Functional capacities of human IgM memory B cells in early inflammatory responses and secondary germinal center reactions

“…− memory B cells has been identified (18)(19)(20). However, the adult human peripheral blood (PB) B-cell pool also includes about 15% IgM…”