CD28 and neoplasm: In co-cultures of Klf4(f/f) or Klf4(f/f);Lys-Cre CD11b+ tumor cells with splenic T cells stimulated with anti-CD3 and anti-CD28, we did not observe a difference in CD8 T cell proliferation (not shown), suggesting that increased proliferation also does not explain the observed increase in T cell frequency.