BCR and B-cell chronic lymphocytic leukemia: The importance of antigenic stimulation through the BCR in CLL development and evolution is evidenced by: (i) restrictions in the immunoglobulin heavy variable (IGHV) gene repertoire expressed by the clonotypic BCRs; (ii) different prognosis of patients with different IGHV gene mutational status; and, (iii) the existence of subsets of patients sharing BCRs with restricted, quasi-identical immunoglobulin sequences (stereotyped BCRs).