Early studies suggested that gut microbiota plays a key role in defining the B cell receptor (BCR) repertoire (9), thus stimulation of alloantigens derived from distinct microbial species might be involved in the development and proliferation of CLL-specific B cell clones, and thereby might potentially stand behind the interindividual variability of clinical outcomes. The gene discussed is BCR; the disease is B-cell chronic lymphocytic leukemia.