Development of immature T-cell lymphomas in Ik^Pax5 mutant mice. (A-C) Histologic analysis of the lymphomas in the Ik^Pax5/+ tumor mouse 80. A hematoxylin and eosin-stained section of the thymus (A) reveals the characteristic appearance of lymphoblastic lymphoma. The heart (B) and lung (C) are massively infiltrated by lymphoma cells. (D-E) Immunophenotype of immature T-cell lymphomas in the thymus (D) and spleen (E) of Ik^Pax5/+ and Ik^neo/+lck-cre mice.