Extracellular vesicle-mediated transfer of constitutively active MyD88 engages MyD88 and activates signaling.

The link between inflammation and cancer is particularly strong in Waldenström macroglobulinemia (WM), a diffuse large B-cell lymphoma wherein the majority of patients harbor a constitutively active mutation in the innate immune-signaling adaptor myeloid differentiation primary response 88 (MyD88). MyD88Leu265Pro (MyD88) constitutively triggers the myddosome assembly providing a survival signal for cancer cells. Here, we report detection and a functional role of MyD88 in the extracellular vesicles (EVs) shed from WM cells. MyD88 was transferred via EVs into the cytoplasm of the recipient mast cells and macrophages, recruiting the endogenous MyD88 that triggered the activation of proinflammatory signaling in the absence of receptor activation. Additionally, internalization of EVs containing MyD88 was observed in mice with an effect on the bone marrow microenvironment. MyD88-loaded EVs were detected in the bone marrow aspirates of WM patients thus establishing the physiological role of EVs for MyD88 transmission and shaping of the proinflammatory microenvironment. Results establish the mechanism of transmission of signaling complexes via EVs to propagate inflammation as a new mechanism of intercellular communication.