CD19 and leukemia: Furthermore, analysis of CD45 + cells circulating in the blood (Additional file 2: Figure S2H) demonstrated that a small subset (5/15 analyzed mice) of aged Eμ-XPO1WT, Eμ-XPO1E571G, and Eμ-XPO1E571K mice spontaneously developed a circulating leukemia characterized by expansion of CD5+/CD19+ and CD19+/B220dim B lymphocytes (Fig. 2d).