Based on the fact that T lymphocytes from B-CLL patients have a phenotype of activated cells, that is, HLA-DR+, CD38+, CD45RO+, CD11c+, CD69+, CD71+, CD40L+ (Dianzani et al, 1994; Van den Hove et al, 1998; Scrivener et al, 2001), it can be suggested that the loss of CD28 molecule on T lymphocytes before culture is related to a prolonged in vivo activation of these cells. The gene discussed is CD28; the disease is B-cell chronic lymphocytic leukemia.