Transcriptome analysis of in vitro generated plasmablasts dervied from Waldenström macroglobulinemia (WM) or heathly control B-cells

The ability to model WM B-cell differentiation using an in vitro system was validated in comparison to healthy cells. The stimuli used initially were CD40L and F(ab’)2 anti-IgG/M, a combination which mimics T-cell dependent activation. Using these conditions, WM B-cells generated mature plasma cells that closely resemble those from healthy controls. Since WM cells harbour the characteristic gain-of-function MYD88L265P mutation, it was also of interest to determine the impact of TLR signals on the differentiation process. In contrast to the expectation of enhanced survival, WM cells exhibited a profoundly deleterious response to R848 + F(ab’)2 anti-IgG/M stimulation, with a sharp decline in population from the initiation of culture and a failure to generate plasma cells. RNA sequencing was performed on material harvested from differentiating cells at day 6 of culture within the in vitro system to assess the underlying gene expression changes that accompanied the two types of stimulation. The samples consisted of 3 healthy controls with matched samples for both CD40L and R848 stimulation and a total of 6 WM samples. Examination of the transcriptomes revealed that WM plasmablasts exhibit elevated expression levels of genes associated with TLR and NF-κB signaling, but reduced levels of genes associated with plasma cell re-programming. This is particularly pronounced in cells treated with the TLR7 agonist R848, suggesting an uncoupling of TLR signaling from plasma cell differentiation in WM. mRNA profiles of plasmablasts generated from CD40L or R848 stimulated B-cells derived from healthy donors or Waldenström macroglobulinemia (WM) patients