Normal and malignant B-cell development with special reference to Hodgkin's disease

Area of Science:

• Immunology
• Oncology
• Molecular Biology

Background:

• B lymphocytes undergo rigorous selection during development, including surface immunoglobulin (Ig) expression and germinal center (GC) reactions.
• GCs are crucial for B cell maturation, involving somatic hypermutation and selection for high-affinity antibodies.
• Hodgkin's disease (HD) is a lymphoid malignancy, and the origin of its characteristic Hodgkin and Reed-Sternberg (H-RS) cells remains a key question.

Purpose of the Study:

• To investigate the B-lineage origin and clonality of Hodgkin and Reed-Sternberg (H-RS) cells in primary Hodgkin's disease (HD).
• To analyze the presence and nature of somatic mutations in the V gene rearrangements of H-RS cells.
• To determine if H-RS cells originate from germinal center B cells and understand their survival mechanisms.

Main Methods:

• Micromanipulation of single H-RS cells from frozen HD tissue sections.
• Polymerase chain reaction (PCR) analysis of rearranged V genes (VH and V kappa/V delta) from isolated H-RS cells.
• Sequencing and analysis of somatic point mutations within the identified V gene rearrangements.

Main Results:

• Clonal VH and/or V kappa/V delta gene rearrangements were detected in 9 out of 10 primary HD cases, confirming B-lineage origin and clonality of H-RS cells.
• Somatic mutations were identified in all clonal VH gene rearrangements analyzed.
• Four cases exhibited mutations leading to stop codons in in-frame V gene rearrangements, suggesting a disruption of normal B cell selection processes.

Conclusions:

• H-RS cells represent a clonal population derived from the B-cell lineage.
• The presence of somatic mutations, including stop codons, in H-RS cells indicates their origin from germinal center B cells.
• H-RS cells likely escape apoptosis through a transforming event, despite acquiring mutations that would normally lead to cell elimination within the germinal center.