Murine B-1 cells were first discovered as Ly-1+ (now CD5+) B cells in early 1980s by Kyoko Hayakawa in Herzenberg’s lab at Stanford University, fueled by the motivation to find the physiological counterpart to human CD5-expressing chronic B-cell leukemia (B-CLL) cells (8, 9). Here, CD5 is linked to B-cell chronic lymphocytic leukemia.