A small number of transcription factors, including Blimp1 (Prdm1), Bcl6, T-bet (Tbx21), Tcf7, and Eomes, are known to be important in the regulation of effector and memory CD8+ T-cell differentiation.5, 6, 7, 8, 9, 10, 11 Quantitative RT-PCR analysis revealed that Smad4-deficient Kb-ova+CD8+ splenic T cells expressed reduced levels of Prdm1 and Tbx21 transcripts but enhanced levels of Bcl6, Tcf7, and Eomes transcripts 7 days after LM-OVA primary infection, as compared to Smad4-sufficient counterparts (Figure 7a). This evidence concerns the gene TBX21 and infection.