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Título
Study of IGH sequences in low-count monoclonal B-cell lymphocytosis
Autor(es)
Fecha de publicación
2022
Editor
Universidad de Salamanca
Citación
Serrano Lozano J. Study of IGH sequences in low-count monoclonal B-cell lymphocytosis [TFM]. Universidad de Salamanca; 2022.
Resumen
Low-count monoclonal B-cell lymphocytosis (MBLlo) is defined by the presence of
<0.5 × 10! clonal B-cells/L in blood in the absence of any other symptoms or signs of a
neoplastic lymphoproliferative disorder. It is still unclear whether MBLlo represents a pre-
malignant state prior to chronic lymphocytic leukemia (CLL) or it relates to a physiological
immunosenescent process. The molecular and biochemical characteristics of the B-cell
receptor (BCR) including the specific immunoglobulin heavy-chain (IGH) sequences
have been related to disease behavior in CLL. In MBLlo, few studies have been reported
of IGH sequences on the clonal B-cells, mostly due to their low counts in blood.
Here, we set up a workflow adapted to the low MBLlo clonal B-cell numbers aimed at
more efficiently characterize genetically and molecularly the IGHV rearrangements of
the BCR of MBLlo cases. We also compare genetic and molecular characteristics of the
BCR of MBLlo vs MBLhi and CLL B-cell clones, and their impact on the behavior of MBLlo
clonal B-cells during follow-up.
MBLlo clonal B-cells were isolated from blood of otherwise healthy individuals by high-
sensitive flow cytometry. Two different multiplex PCR protocols for IGHV sequencing
were applied, depending on the number of MBLlo clonal B-cells available, using a
threshold of 50,000 cells for protocol selection.
The new workflow set up allowed us to increase the number of MBLlo cases included in
out cohort (N=34), for subsequent comparison of IGHV sequences to two MBLhi (N=73)
and CLL (N=138) cohorts. The IGHV3-7 gene sequence was more frequently found in
MBLlo subjects, whereas IGHV3-23 was highly represented in MBLhi patients. No
significant differences were reported in D segments, while IGHJ4 was significantly more
frequent in MBLlo and IGHJ6 in CLL. Compared to other J-gene segments, clonal B-cells
with IGHJ6 show a more immature origin and present longer HCDR3 sequences.
Nevertheless, this BCR characteristic showed no significant impact in the behavior of the
MBLlo clone during follow-up; however a tendency towards a greater size of MBLlo clones
was observed among IGHJ6 cases.
The new workflow here proposed proved to be a useful tool to increase the efficiency of
the characterization of the BCR sequences of MBLlo cases with low clonal B-cells
numbers revealing unique BCR sequences vs MBLhi and CLL.
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