Aberrant extrafollicular B cells, immune dysfunction and myeloid inflammation precede malignancy in Waldenstrom macroglobulinemia

Waldenstrom macroglobulinemia (WM) and its precursor IgM gammopathy are distinct disorders characterized by the growth of mature IgM-expressing B cell clone predominantly in the bone marrow. Here we show that these disorders originate in the setting of expansion of genomically aberrant extrafollicular B cells, immune dysfunction and myeloid inflammation that begins before the expansion of the malignant clone. Host response to these early lesions involves the induction of tumor-specific T cell immunity that may include MYD88 mutation-specific responses. Hematopoietic progenitors carry the oncogenic MYD88 mutations characteristic of the malignant WM clone. These data provide an example of how oncogenic mutations in earlier progenitors may create the milieu promoting the evolution of malignant phenotype in differentiated cells. Overall design: 7 bone marrow specimens each from patients with diagnosis of MGUS or Waldenstrom were obtained.4 healthy donors specimens were purchased from All Cells, Inc.. Bone marrow mononuclear cells (BMMNCs) were stained with custom panels of metal conjugated antibodies according to manufacturer-suggested concentrations (Fluidigm). Gene expression and cell surface libraries were prepared according to the protocol from 10X Genomics. Exome capture was performed using the IDT xGen v1 capture kit (Integrated DNA Technologies) according to manufacturer's instructions. The presence of WM-specific T cells in blood or bone marrow was quantified both directly ex vivo and after in vitro stimulation with autologous tumor loaded DCs using a 16h ELISPOT assay.