The malignant potential of DLCs. The percentage of tumor cells was determined by FACS analysis in a population of splenocytes from BCL₁ wild-type or DLC-containing spleens. Naive animals were then injected with graded numbers of wild-type BCL₁ tumor cells (▵), DLC tumor cells (□), or wild-type BCL₁ tumor cells pulsed with 100 μg MαBCL₁Id, and co-mixed with 10⁶ splenocytes from BCL₁ -Id–immunized mice (○) or wild-type BCL₁ tumor cells admixed with a pool of 10⁶ splenocytes from mice containing 0.72% DLCs (•). Cell numbers were 100 (not shown), 30, 10, 6 (not shown), 3, and 1 (not shown). A Breslow-Day test was used to examine the differences between BCL₁ and DLC treatment groups across cell number groupings for the occurrence of splenomegaly. Comparisons of time to splenomegaly across treatment groups were provided by numbers of cells entered using a log-rank test (product-limit survival estimates enter into this computation). Multiple comparisons between pairs of treatments were accomplished using a Bonferonni correction to the P values for significant results. Mantel-Haenszel χ2 tests were used to provide an indication of the tendency to increase the occurrence of splenomegaly with increased cell numbers. In comparing BCL₁ to DLCs for occurrence of splenomegaly, the Breslow-Day test comparing equal odds ratios of occurrence between the BCL₁ and DLCs across cell numbers was not significant (P = .627). The overall odds ratio estimate is 6.103 for likelihood of splenomegaly from BCL₁ compared with DLCs. The comparison by log-rank test for time to splenomegaly for mice receiving DLCs versus the other treatment groups was significantly different for cell numbers (P values in parentheses) of 100 (.0001), 30 (.0001), 10 (.0031), and 6 (.0194). No statistical difference was observed when 3 (.351) or 1 (.085) cells were injected. (Analogous results were also seen when the data were analyzed by a standard t-test.) There were no statistical differences in occurrence of splenomegaly or time to splenomegaly among the groups (BCL₁ , treated BCL₁ , or the BCL₁ plus DLCs). Mantel-Haenszel statistics indicate an increased occurrence of splenomegaly for increased cell numbers (P values in parentheses): BCL₁ (.001), DLC (.001), and treated BCL₁ (.005).