Vav1−/− Vav2−/− double knockout mice and Vav1−/− Vav2−/− Vav3−/− triple knockout mice have a more severe B cell deficiency, including a developmental block at the immature/transitional B cell stage in bone marrow and spleen, reduced serum level of IgM and IgG, defective response to TI and TD antigens and greatly compromised cell proliferation and calcium flux upon BCR stimulation (42). This evidence concerns the gene VAV1 and B cell deficiency.