Interestingly, a frequently observed stereotypic BCR was the CLL#2 BCR (IGHV3–21 in combination with IGHJ6 with a short HCDR3 length of 9 amino acids), which is the most common stereotypic BCR seen in CLL patients and is associated with an aggressive form of CLL [17, 40]. Here, BCR is linked to B-cell chronic lymphocytic leukemia.