JAK2 and neoplasm: Moreover, an increase of Gr1+CD11b+ cells (MDSC) in the spleen of tumor-free mice treated with VEGF-A compared with control mice has been observed, and this effect is mediated by VEGFR2 (32) and activation of JAK2 (JAnus Kinase 2) and the transcription factor STAT3 (signal transducer and activator of transcription 3) downstream (43).