Two studies of CD5 phosphorylation in CLL cells, one showing that active Lyn mediates the recruitment of SHP-1 to tyrosine phosphorylated CD5 to contribute to apoptosis resistance in CLL cells [104] and a second showing that constitutive phosphorylation of CD5 promotes expression of genes involved in the malignant phenotype of CLL cells, suggest that such negative signaling may be mediated by CD5 [105]. This evidence concerns the gene CD5 and B-cell chronic lymphocytic leukemia.