The role of the spleen in tumor growth kinetics of the murine B cell leukemia (BCL1).

BCL1 is a transplantable B cell leukemia resembling human chronic lymphocytic leukemia-lymphoma maintained by cell passage in BALB/c mice. After BCL1 inoculation (10(7) cells), all mice developed extreme B lymphocytosis in the blood (less than or equal to 440,000 lymphocytes/mm3) and marked splenomegaly (50 times normal nucleated cell numbers). BCL1 infiltrated the spleen before peripheral leukemia was overt (3 days vs 28 days, respectively). BCL1 development in splenectomized mice was characterized by a delayed onset of leukemia (greater than 20,000 cells/ mm3 at 59 vs 28 days in intact mice), doubled median survival (102 vs 53 days, respectively), and reduced peak level of leukemic counts in the blood (125,000 vs 440,000 cells/mm3). Early splenectomy at different time intervals, ranging between 1 hr to 3 days after BCL1 inoculation, significantly delayed onset of the disease and prolonged survival, indicating that homing to the spleen occurred as early as 1 hr after inoculation. Splenectomy at 7 days still delayed onset of leukemia but did not affect survival. No significant effect on BCL1 kinetics was noticed when splenectomy was done on day 21. All splenectomized mice showed significantly lower peripheral blood counts as compared to intact mice (98,000/mm3 vs 440,000/mm3, respectively). The data show that the spleen plays a major role in the pathogenesis and prognosis of BCL1.