Loss of Par-4 in the Eμ-Tcl1–transgenic mice delays CLL growth and increases survival. Leukemic status in Par-4^+/+ and Par-4^−/− EµTcl1 mice was measured by staining of peripheral blood lymphocytes for CD5⁺CD19⁺ cells. Animals died of natural progression of disease or were euthanized due to poor body conditions for humane reasons. (A) Percentage of CLL cases detected with age of Par-4^+/+Tcl1 and Par-4^−/−Tcl1 cohorts over time. P = .0002 comparing the 2 curves by log-rank test (n = 16, Par-4^+/+Eμ-Tcl1; n = 10, Par-4^−/−Tcl1). (B) Effect of Par-4 loss on the survival of Eµ-Tcl1 mice. Survival curve represents a total of 17 Par-4^+/+ Tcl1 mice and 9 Par-4^−/−Tcl1 mice. P = .0472 comparing the 2 curves by log-rank test. (C) Tissues from Par-4^−/−Tcl1 mice were harvested and expression of Par-4 and Tcl1 proteins was determined by western blot analysis. Par-4 was detected in the spleen of Par-4^+/+Tcl1 mouse, but was not present in any of the tissues of the Par-4^−/−Tcl1 mouse. (D) Spleens from multiple Eμ-Tcl1 mice and Par-4^−/−Tcl1 mice were harvested and total protein was isolated. Immunoblots were probed for Par-4 and p21. Protein expression was normalized to β-actin. LN, lymph node; Mesen. LN, mesenteric lymph node.