CD5 and B-cell chronic lymphocytic leukemia: Similar to human CLL and a variety of transgenic mouse models, the de novo animal model, New Zealand Black mouse strain, is characterized by age-associated CLL-like symptoms such as splenomegaly and CD5+ B1 cell hyper-proliferation with aberrant expression of Pax5, Bcl-2 and Cyclin-D1 among others [5].