Loss of a chromosomal region with synteny to human 13q14 occurs in mouse chronic lymphocytic leukemia that originates from early-generated B-1 B cells

Abstract

A common feature of B cell chronic lymphocytic leukemia (CLL) is chromosomal loss of 13q14, containing the miR15a/16-1 locus controlling B cell proliferation. However, CLL etiology remains unclear. CLL is an adult leukemia with an incidence that increases with advancing age. A unique feature of CLL is biased B cell antigen receptor (BCR) usage, autoreactivity with polyreactivity, and CD5 expression, all suggest a role for the BCR in driving CLL pathogenesis. Among human CLLs, BCRs autoreactive with non-muscle myosin IIA (AMyIIA) are recurrent. Here we identify an unmutated AMyIIA BCR in mouse, with distinctive CDR3 segments capable of promoting leukemogenesis. B cells with this AMyIIA BCR are generated by BCR-dependent signaling during B-1 fetal/neonatal development with CD5 induction, but not in adults. These early-generated AMyIIA B1 B cells self-renew, increase during aging, and can progress to become monoclonal B cell lymphocytosis, followed by aggressive CLL in aged mice, often with loss of a chromosomal region containing the miR15a/16-1 locus of varying length, as in human CLL. Thus, the ability to generate this defined autoreactive BCR by B1 B cells is a key predisposing step in mice, promoting progression to chronic leukemia.

Early generated B1 B cells with restricted BCRs become chronic lymphocytic leukemia with continued c-Myc and low Bmf expression

“…When we increased the frequency of cells expressing this ATA BCR by μ Ig transgenesis on a C.B17 background (BALB/c with congenic C57BL/Ka IgM allele), predominant expres-sion of ATA BCR by B1 B cells occurred, including at the neonatal B1a stage , and ATA μκTg exhibited a higher incidence of CLL/lymphoma. This was also illustrated by set 3 V H Q52-1/V k 9 anti-nonmuscle myosin IIA BCR among stereotyped BCRs; this BCR is rare among B1 B cells, but fostering progression to CLL by Ig transgenesis (Hayakawa et al, 2016). Thus, expression of specific BCR, rather than frequency itself among the self-renewing B1 B cell pool, is key for progression to CLL by B1 B cells.…”

“…When sequences were not recovered, specifically for V k 9-96 (ce9) and V k 1-117 (cr1) κ, 5′ RACE cloning was done using the SMA RTer RACE cDNA amplification kit (Takara Bio Inc.). For single-cell sequencing, individual cells were deposited using a FAC SAriaII (BD), directly onto either AmpliGrid AG480F slides (Beckman Coulter), or onto 96-well plates prepared with SuperScript III RT kit (Life Technologies) as previously described (Ichikawa et al, 2015;Hayakawa et al, 2016). The efficiency of obtaining sequences was 70-90%.…”

Early Generated B-1–Derived B Cells Have the Capacity To Progress To Become Mantle Cell Lymphoma–like Neoplasia in Aged Mice

“…This early B-1 B1a cell origin was confirmed by the adoptive transfer of B1a cells present in young mice, including d10 neonatal spleen B1a cells (6). In these B-1 derived B cell leukemia/lymphoma, chromosome loss, syntenic to the 13q14 loss found in human CLL and MCL, also occurred (7). These results suggested that a portion of aged human CD5 + leukemia/lymphoma may be derived from early generated B cells as found in mice.…”

A Hard(y) Look at B-1 Cell Development and Function

“…B-CLL is characterized not only by CD5 expression but also by a skewed BCR repertoire encoding auto- and poly-reactive antibodies (100), all features they have in common with B-1 cells. In their most recent studies the group identified a non-mutated BCR CDR3-region in B-1 cells of mice that encoded binding to myosin IIA, a specificity recurrent among human B-CLL (101). Interestingly, they observed that B-1 cells with that specificity could expand greatly with age and eventually developed into CLL.…”