Clonal preleukemic cells expressed p27^Kip1. p27^Kip1 expression was determined by Western blotting and normalized to β-actin expression. (A) Western blot of purified polyclonal CD8⁺ T cells of 2 mice of each genotype, and of 2 clonal preleukemic CD8m T cells from 2 DM mice at 14 months, sorted based on their Vβ expression (DM1 and DM8). DM indicates Cdkn1b^+/−/MTCP1^TG; Tg, MTCP1 transgenics; Htz, Cdkn1^+/−; and WT, wild type. (B) Relative p27^Kip1 expression normalized to β-actin expression, and to mean expression of wild-type animals. Three mice of each genotype and the 2 sorted clonal populations were analyzed. Results obtained from polyclonal populations were pooled according to the Cdkn1b status. Significance of between-group analyses (brackets) determined by Student t test is indicated as follows: NS, nonsignificant difference; *P = .02; **P = .002.