Influence of Toll-like receptor (TLR)- and other B-cell signalling pathways on MyD88-mutation-mediated lymphomagenesis

Abstract

With up to 40% of cases worldwide, diffuse large B-cell lymphoma (DLBCL) is the most common subtype of lymphoma (Li et al., 2018b, Stewart et al., 2014). The more aggressive activated B-cell like (ABC) subtype of DLBCL only has a 5-year survival rate of about 30% and more than 50% of ABC DLBCL cases have mutations in molecules involved in NF-κB activation. One of these mutations is the MYD88 L265P mutation, which is present in almost 30% of ABC DLBCL cases. MyD88 is an adaptor molecule of Toll-like receptors (TLR) and its downstream effectors include many pro-survival and pro-proliferation signals, such as NF-κB hyperactivation. It is thus of interest to better understand and subsequently exploit the MYD88 L265P mutation for therapeutic purposes, such as Toll-like receptor inhibition.

In this study, it was assessed if B-cells with the MYD88 L265P mutation still depend on upstream TLR signals, which would make TLR inhibitors an attractive target for therapies, or if MyD88 L265P is independent of upstream signals. For this purpose, a mouse model that mimics human DLBCL with B-cell specific expression of Myd88p.L252P , Bcl2 amplifications and Gfp was used and PET-MR imaging with radioactive glucose to assess glucose metabolism and radioactive thymidine to assess proliferation was performed in these mice. Additionally, the distribution of B-cells within the DLBCL mouse model was assessed using in vivo GFP scans. IgM expression as well as IL-6 and IL-10 production of B-cells in these mice was analysed in vitro and in vivo using ELISA. Finally, an evaluation of CD19-antibody-based PET-MR imaging in these transgenic DLBCL mice was performed in a proof-of-concept approach.

We found that the effect of MyD88 L265P is indeed exacerbated by upstream TLR signals, supporting further research to be done on TLR(9) inhibitors. Secondly, we could show that in MyD88L265P -mutated mice, more B-cells accumulate in the abdomen than in unmutated mice, suggesting potential TLR ligands, for example from the microbiota, to be present in the abdomen. Cytokine levels and IgM expression did not differ between mutated and unmutated B-cells in vitro and in vivo. Finally, we could demonstrate that CD19-antibody-based PET-MR imaging of lymphomas in our transgenic DLBCL mouse model is possible. This supports that CD19-based PET imaging is indeed possible for MYD88L265P -mutated lymphoma and could help to improve diagnostics and treatment monitoring of MYD88L265P -mutated lymphoma. Collectively, this study supports that MYD88 L265P is an important driver of DLBCL.