IL4 and diffuse large B-cell lymphoma: To test whether D419 mutation alters cell growth in the presence of sustained cytokine signaling, we developed a co-culture model wherein DLBCL cells are cultured in a transwell above a stromal cell line that constitutively produces IL-4 (293-IL-4; Fig. 1F), leading to sustained STAT6 phosphorylation (Fig. 1G).