CD20 and CD19 promote proliferation driven by the IgM-TLR9-L265P MyD88 complex.

Area of Science:

• Immunology
• Oncology
• Molecular Biology

Background:

• The L265P MyD88 mutation is a key driver in approximately 30% of activated B cell-like diffuse large B cell lymphoma (ABC DLBCL) cases.
• This mutation leads to the formation of the My-T-BCR complex, involving MyD88, Toll-like receptor 9 (TLR9), and B cell receptor (BCR) components like IgM, which drives malignant cell proliferation.

Purpose of the Study:

• To investigate the role of B cell surface molecules CD19 and CD20 in modulating proliferation driven by the My-T-BCR complex in ABC DLBCL.
• To elucidate the distinct mechanisms by which CD19 and CD20 influence My-T-BCR complex-mediated proliferation.

Main Methods:

• Utilized the interleukin-3 (IL-3)-dependent Ba/F3 cell line engineered to express the IgM complex (IgM, CD79a, CD79b) and TLR9.
• Assessed proliferation in response to anti-IgM antibody and TLR9 ligand (CpG-B) in cells with and without L265P MyD88, CD19, and CD20.
• Examined signaling pathways, including AKT phosphorylation, and cell surface molecule expression in response to these stimuli.

Main Results:

• CD19 specifically enhanced proliferation in L265P MyD88-expressing cells, mediated by IgM and TLR9, and promoted IgM-dependent AKT phosphorylation.
• CD20 enhanced proliferation in both wild-type and L265P MyD88-expressing cells, uniquely enabling IgM-mediated proliferation in L265P MyD88 cells by increasing cell surface IgM expression.
• Disruption of CD19, CD20, or TLR9 impaired anti-IgM antibody-mediated growth in the ABC DLBCL cell line TMD8.

Conclusions:

• CD19 and CD20 play differential roles in promoting proliferation driven by the My-T-BCR complex in ABC DLBCL.
• CD19 primarily impacts signaling downstream of the complex, while CD20 enhances complex formation by increasing IgM expression.
• These findings highlight CD19 and CD20 as potential therapeutic targets in ABC DLBCL harboring the L265P MyD88 mutation.